State budgetary educational institution of secondary school No. 1 “Education Center” urban settlement. Construction ceramics of the municipal district of Volzhsky, Samara region
Subject: " Chemical experiment as a means of developing interest in chemistry"
Chemistry teacher
Lyukshina Natalia Alexandrovna
Introduction
Chemistry is a theoretical-experimental science. Therefore, in the process of studying it, the most important method is experiment as a means of obtaining specific ideas and solid knowledge.
Entertaining experiments, being part of the experiment, instill a love of chemistry, create interest in the subject in extra time from classes, contribute to more successful mastery of chemistry, deepening and expanding knowledge, developing skills for independent creative work, and instilling practical experience in working with chemical reagents and equipment.
Demonstration experiments, having an element of entertainment, contribute to the development of students’ skills in observing and explaining chemical phenomena. A chemical experiment is the most important method and the main means of visualization in the lesson. Experiment is a complex and powerful tool of knowledge. The widespread use of experiment in teaching chemistry is one of the most important conditions for students’ conscious and solid knowledge of chemistry. A chemical experiment is the most important way to connect theory with practice by transforming knowledge into beliefs.
The main goal of this report is to awaken students’ interest in chemistry from the first lessons and to show that this science is not only theoretical.
A chemical experiment based on creative independent activity helps to introduce students to the basic methods of chemical science. This occurs when the teacher often uses it in a way that resembles the inquiry process in chemical science, which works particularly well where experimentation is the basis of a problem-based approach to teaching chemistry. In these cases, experiments help confirm or reject the assumptions made, as happens in scientific research in chemistry. One of the goals of this report is to show how interesting even the most basic information from a school chemistry course can turn out to be, if only you take a closer look at it. I conducted demonstration experiments during lessons in eighth grade. As evidenced by a survey of students, the work carried out aroused interest in studying chemistry. During the experiments, schoolchildren began to think and reason logically. While carrying out this work, I realized that a chemical experiment is the core on which chemical education rests. The movement towards truth begins with surprise, and for most schoolchildren it arises precisely in the process of experimentation, when the experimenter, like a wizard, transforms one substance into another, observing amazing changes in their properties. In these cases, experiments help confirm or reject the assumptions made, as happens in scientific research in chemistry. A passion for chemistry almost always begins with experiments, and it is no coincidence that almost all famous chemists from childhood loved to experiment with substances, thanks to which many discoveries were made in chemistry, which can only be learned from history.
Throughout the history of chemistry as an experimental science, various theories have been proven or disproven, various hypotheses have been tested, new substances have been obtained and their properties have been revealed. Currently, chemical experiment is still the main tool for testing the reliability of knowledge. A chemical experiment is always carried out with a specific purpose, it is clearly planned, special conditions, necessary equipment and reagents are selected for its implementation.
Of particular importance is the question of the place of experiment in the learning process. Learning experiences are the means of learning. In one case, an experiment can be carried out after an explanation and, with its help, answer certain questions. The experiment should lead students to an understanding of the most important laws of chemistry.
In the process of teaching chemistry, an experiment is
firstly, a unique object of learning,
secondly, by research method,
thirdly, the source and means of new knowledge.
Therefore, it is characterized by three main functions:
educational, because it is important for students to master the basics of chemistry, pose and solve practical problems, and identify the importance of chemistry in modern life;
educating, because it contributes to the formation of the scientific worldview of schoolchildren, and is also important for orienting schoolchildren to relevant professions;
developing, since it serves to acquire and improve general scientific and practical skills.
Teaching chemistry at school should be visual and based on chemical experiments.
The real and virtual experiment should complement each other. A virtual chemical experiment is possible when working with toxic reagents.
Theoretical part of the experience
Chemistry is an experimental science. The Latin word "experiment" means "test", "experience". A chemical experiment is a source of knowledge about matter and chemical reactions and is an important condition for enhancing students’ cognitive activity and cultivating interest in the subject. Even the brightest image on a screen is no substitute for real-life experience, as students must observe and study the phenomena themselves.
Visualization and expressiveness of experiments is the first and main requirement for an experiment.
The short duration of the experiments is the second requirement for the experiment.
Convincingness, accessibility, reliability - this is the third requirement for an experiment.
A very important requirement is the safety of the experiments performed. In the chemistry classroom there is a stand with safety rules that must be strictly followed.
Through observation and experimentation, students learn the diverse nature of substances, accumulate facts for comparisons, generalizations, and conclusions.
From a cognitive point of view, a chemical experiment can be divided into two groups:
1. Educational experiment , which gives students knowledge about the subject being studied (for example, experiments characterizing the chemical properties of substances).
2. Visual experiment , confirming the teacher’s explanations.
Cognitive experiences can be divided into the following groups according to their meaning:
Experiments are the starting source of knowledge of the properties of substances, conditions and the mechanism of chemical reactions. Carrying out such experiments is associated with posing and solving problems of a problematic nature, and conclusions from observations act as generalizations, rules, definitions, patterns, etc.
Experiments, the cognitive value of which consists in confirming or denying the stated hypothesis. Generalized conclusions from such experiments help to solve fundamental questions about the school chemistry course, for example, the question of genetic relationships between classes of chemical compounds, etc.
Experiments illustrating conclusions and conclusions drawn from the study of theoretical principles.
Experiments that improve conclusions and consolidate students’ knowledge about the properties of substances and their transformations.
Experiments, the cognitive significance of which at a given stage is indirect in nature (examples of chemical transformations without revealing the essence of the processes).
Test experiments and experimental tasks. Their cognitive significance for students is expressed in the elements of self-control.
If an experiment is used to create problematic situations or to solve problematic problems, it should be vivid and memorable, unexpected and convincing for students, it should capture the imagination and have a strong influence on the emotional sphere. When organizing and performing a chemical experiment in this way, students delve deeply into the essence of the experiments, think about the results and try to answer questions that arise during the experiment.
A correctly conducted experiment and clear conclusions from it are the most important means of developing the scientific worldview of students.
In addition, a chemical experiment plays an important role in the successful solution of educational tasks in teaching chemistry:
As the original source of knowledge of phenomena;
As the only means of proving a hypothesis, a conclusion;
As the only means for developing the improvement of practical skills;
As an important means for developing, improving and consolidating theoretical knowledge;
As a method of testing students' knowledge and skills;
As a means of developing students’ interest in studying chemistry, developing their powers of observation, inquisitiveness, initiative, desire for independent search, improving knowledge and applying it in practice.
The school chemical experiment is of great educational importance for the polytechnic training of students.
In the practice of teaching chemistry, it is traditional to divide a chemical experiment into a demonstration experiment, carried out by a teacher, and a student experiment, performed by schoolchildren.
Demonstration experiments are a necessary type of experiment. It is used in the following cases:
when students, especially at the first stages of training, do not sufficiently master the technique of performing experiments, and therefore are not able to perform them independently;
when the technical equipment of the experience is difficult for students or there is no appropriate equipment in sufficient quantity;
when individual laboratory experiments are replaced by demonstration ones in order to save time and in case of insufficient quantities of reagents;
when the demonstration surpasses the experience performed by students in terms of external effect and persuasiveness;
when, due to safety regulations, students are prohibited from using certain substances (bromine, solid potassium permanganate, etc.).
The main requirement for any chemical experiment is the requirement that it be completely safe for students.
The teacher is responsible for the accident both morally and legally. Therefore, preliminary verification of experiments and compliance with all safety requirements are mandatory for everyone working in the chemistry room. The main guarantee of the safety of demonstration experiments is the high technical literacy of the teacher, armed with appropriate safety skills.
Student experimentation is usually divided into laboratory experiments, practical exercises, and home experiments.
The didactic purpose of laboratory experiments is to acquire new knowledge, as they are carried out while studying new material. Practical work is usually carried out at the end of studying a topic, and their goal is to consolidate and systematize knowledge, form and develop students’ experimental skills. According to the form of organization of laboratory experiments: 1) individual, 2) group, 3) collective. The results of experiments should be recorded in workbooks.
Practical classes are:
carried out according to instructions,
experimental tasks.
Practical exercises are a complex type of lesson. Students perform the experiments in pairs according to the instructions in the textbooks.
The teacher needs to monitor the entire class and correct the actions of students. After completing the experiments, each student fills out a report on the form.
Experimental problems do not contain instructions, they only have conditions. Preparation for solving experimental problems is carried out in stages. First, the problems are solved theoretically by the whole class. The student then conducts an experiment. After this, the class begins to perform similar tasks in the workplace.
A home experiment is one of the types of independent work that is of great importance both for developing interest in chemistry and for consolidating knowledge and many practical skills.
SchemeClassification of educational chemical experiment
Educational chemical experiment
Demo
Student
Laboratory experiments
Practical lessons
Workshops
Home experiments
Research
Illustrative
In addition to research work in the form of homework, there are also extracurricular research activities.
Extracurricular research activities of students can be represented by the following forms of participation of schoolchildren in them: school non-governmental educational institution; Olympiads, competition, project activities; intellectual marathons; research conferences of various types; electives, elective courses, elective courses; examination papers.
Research work is possible and effective only on a voluntary basis, like any creativity. Therefore, the topic of scientific research should be: interesting to the student, fascinating for him; feasible; original (it requires an element of surprise, unusualness); accessible; must correspond to the age characteristics of the students.
Educational and research activities contribute to: developing interest, expanding and updating knowledge on the subject, developing ideas about interdisciplinary connections; development of intellectual initiatives creating prerequisites for the development of a scientific way of thinking; mastering a creative approach to any type of activity; training in information technology and working with communications media; receiving pre-professional training; meaningful organization of children's free time. The most common form of defense of research work is the creative defense model.
The creative model of protection assumes:
Design of a stand with documents and illustrative materials on the stated topic, their commentary;
Demonstration of video recordings, slides, listening to audio recordings, presenting a fragment as the basis of a part of the study;
Conclusions on the work made in the form of a presentation of the results;
Scientific work should be:
Research;
Current;
Have practical significance for the author himself and the school.
Creative discoveries and methodological achievements of the teacher
The role of chemistry in solving environmental problems is enormous. In my work I use active learning methods: non-traditional lessons, elective courses, environmental projects, seminars, conferences. The greening of a chemical experiment involves experimental testing of the purity of food products and serves as the basis for creating problematic situations.
2010-2011 academic year
In 2010, I received a certificate of winner of 1st place in the regional scientific and practical conference from the Municipal Educational Institution of Educational Institution TsVR of the Volzhsky municipal district of the Samara region in the 11th grade
The following types of school chemical experiment are distinguished: demonstration experience, laboratory experience, laboratory work, practical work, laboratory workshop and home experiment.
Depending on the nature of the impact on students’ thinking and the methodology for organizing a school chemical experiment, it can be carried out in a research and illustrative form.
The illustrative method is sometimes called the method of ready-made knowledge: the teacher first communicates what should be obtained as a result of the experiment, and then illustrates what was said with a demonstration, or the material being studied is confirmed by conducting a laboratory experiment.
Research is a method in which students are asked to select reagents and equipment for conducting an experiment, predict the result, highlight the main thing in observations and draw their own conclusions. The teacher conducts the experiment as if under the guidance of the students, performing the proposed experimental actions, commenting on the safety rules for conducting the experiment, and asking clarifying questions.
At the first stage of studying chemistry, the illustrative method of conducting demonstration experiments turns out to be more effective than the research method. In this case, students experience less difficulty in subsequently describing observations and formulating conclusions. However, the use of the illustrative method should not be limited only to the teacher’s competent commentary. Students will have stronger knowledge gained as a result of a heuristic conversation built by the teacher during the demonstration. As schoolchildren's readiness for independent observation in the process of studying chemistry increases, it is possible to increase the share of the research method in conducting demonstrations. The correct choice of the form of organizing the experiment is an indicator of the teacher's pedagogical skill.
A school chemical experiment can be divided into a demonstration experiment, when the experiment is shown by the teacher, and a student experiment, performed by students.
The most common and difficult thing to teach is to conduct demonstration experiments in which objects and processes are observed.
A demonstration is an experiment conducted in the classroom by a teacher, laboratory assistant, or sometimes one of the students. The teacher uses this experiment at the beginning of the course to teach students to observe processes, work methods, and manipulations. This arouses students’ interest in the subject, begins to develop their practical skills, introduces them to chemical glassware, instruments, substances, etc. The demonstration experiment is then used when it is too complex for students to complete on their own.
The school uses two types of demonstration experiments:
Demonstrations, when the student observes the objects of the demonstrations directly. In this case, they show substances and carry out various chemical operations with them, for example, heating, burning, or demonstrate experiments in large vessels - glasses, flasks, etc.
2. Indirect demonstrations are used in cases where the processes taking place are little noticeable or poorly perceived by the senses. In these cases, chemical processes are reproduced using various devices. Thus, poorly visible chemical reactions are projected onto a screen using a graphic projector, electrolytic dissociation processes are detected using probes, and the density of solutions is determined using hydrometers.
These two types of demonstrations should be used skillfully and not exaggerate the significance of one of them; for example, all experiments cannot be shown only by projection onto a screen, since in this case students will not directly see the substances and processes occurring. Consequently, they will not acquire specific ideas about them. Sometimes it turns out to be advisable to use a combined technique involving direct and indirect demonstrations, when clearly visible operations are shown in glassware, and individual, poorly visible details are projected onto the screen. Or, during an indirect demonstration, the substances taken and obtained are displayed on the demonstration table (or student tables), and the processes between them are projected onto the screen.
The didactic effect of demonstration experiments depends on such factors as the technique of conducting the experiment and the creation of optimal conditions for the clarity of what the teacher wants to show and prove, i.e. achieving the goal of the experiment.
Requirements for the demonstration experiment:
safety of the experiment;
compliance with the conditions of a certain distance from the objects of observation to the observer, lighting conditions, volumes of substances, sizes and shapes of dishes and devices;
combination of demonstration of experience with teacher commentary.
The last requirement plays a major role in the demonstration, when the teacher, through commentary, guides the observation of the experiment. Conducting an experiment by a teacher can be carried out using either a purely illustrative method or a partially exploratory one.
Thus, in the process of demonstration, three functions of the educational process are carried out: educational, educational and developmental. Demonstration experience allows students to form basic theoretical concepts of chemistry, provides a visual perception of chemical phenomena and specific substances, develops logical thinking, and reveals the practical significance of chemistry. With its help, students are posed with cognitive problems and put forward hypotheses that are tested experimentally. It promotes consolidation and further application of the material being studied.
A student experiment is a type of independent work. It not only enriches students with new knowledge, concepts, and skills, but also proves the truth of the knowledge they have acquired, which ensures a deeper understanding and assimilation of the material. It allows you to more fully implement the principle of polytechnicism - connection with life, with practical activity.
Student experiment is divided into two types: 1) laboratory experiments conducted by students in the process of acquiring new knowledge; 2) practical work that students do after completing one or two topics.
Laboratory experiments are educational and developmental in nature and their role in the study of chemistry is most important.
The purpose of laboratory experiments is to acquire new knowledge and study new material. They initially practice methods of action, with students usually working in pairs.
Practical classes, as a rule, are carried out at the end of studying a topic with the aim of consolidating, concretizing knowledge, developing practical skills and improving students’ existing skills. In practical classes, they conduct experiments independently, using instructions, often individually.
Conducting practical work allows students to apply the acquired knowledge and skills in independent work, draw conclusions and generalizations, and the teacher to assess the level of students’ acquired knowledge and skills. Practical work is a kind of conclusion, the final stage in the study of topics and sections.
Students must prepare for practical work and think through the experiment independently. In many cases, practical work is carried out in the form of experimental problem solving, in high school - in the form of a workshop, when, after completing a number of topics, practical work is carried out in several lessons. A skillfully used chemical experiment is of great importance not only for achieving the set educational goals in teaching chemistry, but also for developing the cognitive interests of students. If a teacher is fluent in a chemical experiment and uses it to help students acquire knowledge and skills, then students study chemistry with interest. In the absence of a chemical experiment in chemistry lessons, students' knowledge of chemistry may acquire a formal connotation - interest in the subject drops sharply.
From the point of view of the learning process, a student experiment should proceed through the following stages: 1) awareness of the purpose of the experiment; 2) study of the proposed substances; 3) assembly or use of a finished device; 4) performing the experiment; 5) analysis of results and conclusions; 6) explanation of the results obtained and the use of chemical equations; 7) drawing up a report.
Each student must understand why he is doing the experiment and how to solve the problem assigned to him. He studies substances organoleptically or with the help of instruments and indicators, examines the parts of the device or the entire device. By performing the experiment, the student masters techniques and manipulations, observes and notices the features of the process, distinguishes important changes from unimportant ones. After completing the experiment, he must write a report.
In practical classes, much attention is paid to the development of practical skills, since their foundations are laid from the very first stages of studying chemistry, and in subsequent classes they are developed and improved.
There are two types of practical classes: those conducted according to instructions and experimental tasks.
Instructions are the indicative basis for students’ activities. It describes in detail each stage of the experiments, provides instructions on how to avoid erroneous actions, and contains information about safety measures when performing the work. Instructions for laboratory experiments and practical tasks must be clear and consistent. However, when performing work, written instructions alone are not enough; the teacher must competently and clearly demonstrate laboratory techniques and manipulations in the process of preliminary preparing students for practical work.
Experimental tasks do not contain instructions, but only conditions. Students must develop a solution plan and implement it independently.
Preparation for practical classes is general in nature. At the same time, material studied in different sections of the topic is used, and practical skills are also formed. In previous lessons, the teacher used the instruments that students will use in the practical lesson, discussed the conditions and features of the experiment, etc.
At the beginning of the practical lesson, it is necessary to have a short conversation about safety rules and key points of work. All instruments used in the work are placed assembled on the demonstration table.
A practical lesson devoted to solving experimental problems is a type of test, so it is conducted somewhat differently than a practical lesson according to instructions.
Students can be prepared to solve experimental problems in stages.
1. First, the whole class solves the problem theoretically. To do this, it is necessary to analyze the conditions of the problem, formulate questions that need to be answered to obtain the final result, and propose experiments necessary to answer each question.
2. One of the students solves the problem theoretically at the blackboard.
3. A student at the blackboard performs an experiment. After this, the class begins to solve similar problems in the workplace.
It is advisable to distribute experimental tasks according to options in order to achieve greater independence and activity of students in the process of work.
When experimentally solving chemical problems, students are required to independently use their skills to conduct chemical experiments to acquire knowledge or confirm assumptions. This ensures the development of their cognitive activity in the process of performing a chemical experiment.
COURSE CURRICULUM
| Newspaper no. | Educational material |
|---|---|
| 17 | Lecture No. 1. Contents of the school chemistry course and its variability. Propaedeutic chemistry course. Basic school chemistry course. High school chemistry course.(G.M. Chernobelskaya, Doctor of Pedagogical Sciences, Professor) |
| 18 | Lecture No. 2. Pre-professional preparation of primary school students in chemistry. Essence, goals and objectives. Pre-professional elective courses. Methodological recommendations for their development.(E.Ya. Arshansky, Doctor of Pedagogical Sciences, Associate Professor) |
| 19 | Lecture No. 3. Profile training in chemistry at the senior level of general education. A unified methodological approach to structuring content in classes of different profiles. Variable content components.(E.Ya. Arshansky) |
| 20 | Lecture No. 4. Individualized technologies for teaching chemistry. Basic requirements for building individualized learning technologies (ITI). Organization of independent work of students at various stages of the lesson in the TIO system. Examples of modern TIOs.(T.A. Borovskikh, candidate of pedagogical sciences, associate professor) |
| 21 | Lecture No. 5. Modular teaching technology and its use in chemistry lessons. Fundamentals of modular technology. Methods for constructing modules and modular programs in chemistry. Recommendations for using technology in chemistry lessons.(P.I. Bespalov, candidate of pedagogical sciences, associate professor) |
| 22 | Lecture No. 6. Chemical experiment in a modern school. Types of experiment. Functions of a chemical experiment. A problem-based experiment using modern technical teaching aids.(P.I. Bespalov) |
| 23 | Lecture No. 7. Ecological component in a school chemistry course. Content selection criteria. Ecologically oriented chemical experiment. Educational and research environmental projects. Problems with environmental content.(V.M. Nazarenko, Doctor of Pedagogical Sciences, Professor) |
| 24 | Lecture No. 8. Monitoring the results of chemistry training. Forms, types and methods of control. Test control of knowledge in chemistry.(M.D. Trukhina, candidate of pedagogical sciences, associate professor) |
Final work. Development of a lesson in accordance with the proposed concept. A short report on the final work, accompanied by a certificate from the educational institution, must be sent to the Pedagogical University no later than February 28, 2007. |
|
P.I. BESPALOV
LECTURE No. 6
Chemical experiment in a modern school
Lecture plan
Types of experiment and methods of its use.
Functions of a chemical experiment.
Problem experiment.
There are three sources of knowledge: authority, reason, experience.
However, authority is insufficient if it does not have
rational basis, without which he produces misunderstanding,
but only acceptance on faith; and reason alone cannot distinguish sophism
from real evidence if he cannot justify
your conclusions from experience.
Roger Bacon
INTRODUCTION
A chemical experiment is the most important method and means of teaching chemistry. The methodology for using a chemical experiment in chemistry lessons has been sufficiently researched and developed by methodological scientists. However, currently there is renewed interest in this topic. This is primarily due to the fact that there is a sharp change in the content of the academic subject, the emergence of propaedeutic and elective courses. All this requires a search for new experiences that fit into the modern content of teaching chemistry at school.
In general, both the educational content and the selection of a chemical experiment depend on the social order of society. This can be observed in the publications of the journal “Chemistry at School”. For example, in the post-war period, when the national economy destroyed by the war was being restored, a large number of articles were devoted to chemical production. The headings “Chemical Experiment” and “Extracurricular Activities” described existing laboratory installations for the production of various substances. Later, agriculture became a priority. Agricultural themes manifested themselves in the synthesis of herbicides, pesticides, various growth stimulants, etc.
TYPES OF EXPERIMENT AND METHODS OF ITS USE
It is well known that school chemistry experiments are classified into demonstration and student experiments. Depending on the purpose and method of organization, student experiments are divided into laboratory experiments, practical exercises and home experiments.
Demonstration experiment
A demonstration chemical experiment is the main means of visualization in the lesson. This is determined by the specifics of chemistry as an experimental science. Therefore, the experiment occupies one of the leading places. It allows not only to identify facts, but also to introduce the methods of chemical science.
The demonstration experiment is conducted by a teacher or laboratory assistant. In some cases, a simple experiment can be demonstrated by a student.
When is a demonstration experiment used in the classroom?
At the beginning of the school course - to instill experimental skills, interest in chemistry, familiarization with utensils, substances, equipment.
When it is difficult for students to complete independently (obtaining ozone).
When it is dangerous for students (explosion of hydrogen with oxygen).
There is no appropriate equipment and reagents.
Well known and requirements for a demonstration experiment.
1. Visibility - a large volume of reagents and glassware, visible from the last rows, there should be no unnecessary parts on the table. To enhance clarity, an overhead projector, a computer, a stage, and color screens can be used.
2. Simplicity – devices should not contain a clutter of unnecessary parts. It should be remembered that the object of study is not the device, but the chemical process occurring in it. The simpler the device, the easier it is to explain the experiment. Therefore, when using the Kipp apparatus, gasometer, or Kiryushkin device, it is necessary to explain the operating principle of the device.
3. Safety – the chemistry teacher is responsible for the lives of students. Therefore, all experiments must be carried out in compliance with safety regulations. When demonstrating experiments with explosions, it is necessary to use a protective screen; when receiving and demonstrating toxic gases - forced ventilation (exhaust), etc.
4. Reliability – unsuccessful experiences cause disappointment in students. Therefore, it is necessary to practice the experiment before the lesson. At the same time, the time spent on its implementation is specified.
5. The technique of performing the experiment must be impeccable. Therefore, if a new experiment is being mastered, it must be well worked out. Mistakes made by the teacher are easily transferred to the students.
6. THE NEED FOR AN EXPLANATION OF DEMONSTRATIONAL EXPERIENCE e n t a. Before demonstrating the experiment, it is necessary to indicate the purpose of the experiment, orient the students’ observations of the experiment, and draw conclusions after the experiment.
Methodology for conducting demonstration experiments
1. Setting the purpose of the experiment: why this experiment is being carried out, what students should be convinced of, what to understand.
2. Description of the device where the experiment is carried out and the conditions for its conduct.
3. Organization of student observations: the teacher must orient students which part of the device should be observed.
4. Conclusions.
It happens that when teaching a lesson, a series of demonstration experiments is used. How to determine the sequence of their demonstration? Let’s look at what you need to be guided by using the topic “Oxygen” as an example.
When studying the topic “Oxygen,” the teacher demonstrates to students the combustion of sulfur, coal, phosphorus and iron in oxygen. The following sequence of demonstrations will be correct: coal combustion, sulfur combustion, phosphorus combustion, iron combustion. This order is explained by the external effect accompanying the combustion of these substances. Coal burns more vigorously in oxygen than in air. The combustion of sulfur in oxygen is accompanied by the appearance of a large blue flame. Phosphorus burns brilliantly in oxygen. And finally, the burning of iron is similar to the burning of sparklers.
If this order is changed, the effect of subsequent reactions will be lower than previous ones, which undoubtedly causes disappointment for students. In addition, we first demonstrate the combustion in oxygen of substances that are flammable in air (C, S, P), and only then the combustion of the non-flammable substance iron. Finally, the first three processes are the interaction of oxygen with non-metals, and the last demonstration is the interaction of oxygen with metals. If the teacher focuses on this, then he forms the systematic knowledge of students.
Thus, when selecting experiences, it is necessary to optimally and harmoniously include them in the outline of the lesson.
Student experiment
Student experiment is divided into laboratory experiments and practical work. Some methodologists also highlight a workshop, which is held at the final stage of studying chemistry.
The didactic goal of laboratory experiments is to acquire new knowledge, because they are carried out when studying new material. Practical work is usually carried out at the end of studying a topic, and their goal is to consolidate and systematize knowledge, form and develop students’ experimental skills.
When performing a student experiment, the following steps must be taken into account:
1) awareness of the purpose of the experience;
2) study of substances;
3) installation of the device (where necessary);
4) performing the experiment;
5) analysis of results;
6) explanation of the results obtained, writing chemical equations;
7) formulation of conclusions and preparation of a report.
According to the form of organization laboratory experiments can be individual, group and collective. It is very important to properly organize students’ activities so that only the allotted time is spent on completing the experiment. This requires careful preparation of training equipment and reagents. Reagent bottles must have labels. If reagents are given in test tubes, they must be numbered, and appropriate notes must be made on the board or on pieces of paper. During the experiments, it is necessary to guide the actions of students. After completing the work, you need to organize a discussion of the results. The results of experiments should be recorded in workbooks. The disadvantage of laboratory experiments is that during their implementation it is impossible to develop experimental skills. This task is performed by practical exercises.
Practical lessons are divided into two types: those carried out according to instructions and experimental tasks. Instructions for practical work provide an indicative basis for students' activities. At the initial stage of studying chemistry, detailed instructions are given with a detailed description of the operations performed. As practical work is completed and experimental skills are mastered, the instructions become more condensed. Experimental problems do not contain instructions, they only have conditions. The student must develop a plan for solving the problem and implement it independently.
Before starting any practical work, the teacher introduces students to the rules of safe work in the chemistry classroom and draws attention to the performance of complex operations. When performing the first practical work, the teacher provides an approximate form of the report and helps students draw conclusions.
Preparation for solving experimental problems is carried out in stages. First, the problems are solved theoretically by the whole class. To do this, the conditions of the problem are analyzed, questions that need to be answered are formulated, and experiments are proposed. Then one student solves the problem at the board theoretically and experimentally proves the correctness of his assumptions. After this, the class begins to perform similar tasks at their workplaces. Experienced teachers gradually introduce experimental tasks into the teaching process. So, for example, when conducting practical work “Obtaining oxygen and studying its properties,” the teacher offers well-performing students the task: “Which of the proposed substances (KNO 3, K 2 SO 4, MnO 2) can be used to produce oxygen?”
Practical lesson is a complex type of lesson. The teacher needs to monitor the entire class and correct the actions of students. Specially trained students in the class - proctors - can provide great assistance to the teacher. This could be a member of a circle, a student interested in chemistry, or simply someone who wants to.
The teacher invites proctors to the chemistry classroom after school hours and invites them to complete the upcoming practical work under his supervision, paying attention to possible errors and subtleties.
Each proctor is then given a record sheet and instructed on how to complete it. Here is a fragment of such a sheet for the practical work “Obtaining copper sulfate.”
Accounting sheet
| Contents of operation | Assessment of operation performance | |||
|---|---|---|---|---|
| Ivanov | Petrov | Sidorov | Sergeev | |
| Take a bottle of sulfuric acid solution so that the label is under your palm | ||||
| Pour 20 ml of sulfuric acid solution into a glass | ||||
| Remove a drop of acid from the neck of the bottle | ||||
| Assemble the tripod correctly and place a glass of sulfuric acid on the grid | ||||
| Place the alcohol lamp under the mesh so that the top of the flame touches the mesh | ||||
| .............................. etc. | ||||
| Cleanliness of the workplace | ||||
| Compliance with safety regulations | ||||
Proctors also need to be taught communication and behavior style. It is important that they approach the assigned task responsibly, are sociable and do not behave arrogantly.
After this, during the lesson, proctors are assigned to supervise a microgroup of 3-4 students sitting at adjacent tables while they perform practical work. If a student performs an operation correctly and independently, without the intervention of a proctor, he will receive 1 point for it; if he makes a mistake while performing the operation, he will receive no points.
The completed accounting sheet is handed over to the teacher upon completion of work and must be taken into account along with checking the report in the notebooks. If students receive a complaint against the proctor, the teacher must look into it and make a fair decision. Proctors not only monitor the work of students, but also provide them with the necessary assistance, explain what is not clear, i.e. perform some teacher functions in their group.
The experience of using this technique at the initial stage of studying chemistry has shown its high effectiveness.
Home experiment
A home chemical experiment is one of the types of independent work for students, which is of great importance both for developing interest in chemistry and for consolidating knowledge and many practical skills. When performing some home experiments, the student acts as a researcher who must independently solve the problems facing him. Therefore, not only the didactic value of this type of student experiment is important, but also the educational and developmental value.
From the first lessons of studying chemistry, it is necessary to direct students to perform experiments not only at school, but also at home. Home experiments include experiments that do not require complex installations and expensive reagents. The reagents used must be safe and purchased from hardware stores or pharmacies. However, when using these reagents, consultation with a teacher is necessary.
The proposed experiments can be of a varied nature. Some are associated with the observation of phenomena (merging solutions of soda and vinegar), others with the separation of a mixture of substances, while still others require explaining the observed phenomena using your knowledge of chemistry. Experimental tasks are also included, in which students do not receive ready-made instructions from the teacher on the technique of performing the experiment, for example, to experimentally prove the presence of salts in drinking water.
It is advisable that older members of the child’s family be present during the experiment.
It is useful for the teacher to create instructions for performing experiments for each topic. Then this direction will be systemic in nature.
An equally important point in the work of students is the preparation of written reports on the results of a home chemical experiment. You can recommend that students write reports in the form they use when performing practical work.
The teacher can systematically review home reports in students' workbooks, as well as listen to students speak about the results of the work done.
FUNCTIONS OF CHEMICAL EXPERIMENT
During the learning process, a chemical experiment performs various functions 1. Let's consider some of them.
Heuristic function of a chemical experiment manifests itself in the establishment of new
A) facts; b) concepts and c) patterns.
a) An example is the reaction of hydrogen gas with copper(II) oxide. By observing this demonstration, students establish that hydrogen, under certain conditions, can react with metal oxides, reducing the metal to a simple substance.
b) A chemical experiment has great potential for the formation of new concepts. For example, when studying the topic “Oxygen,” the teacher demonstrates a method for producing oxygen from hydrogen peroxide. To speed up the process of decomposition of hydrogen peroxide, manganese dioxide is introduced into the test tube. After the reaction is completed, the teacher gives the definition of a catalyst.
c) The function of identifying dependencies and patterns is especially pronounced when studying the topic “Patterns of chemical reactions.” A demonstration experiment allows us to identify the dependence of the rate of a chemical reaction on the nature of the reacting substances, concentration, contact surface of the reacting substances, etc.
Corrective function of a chemical experiment manifests itself in overcoming difficulties mastering theoretical material and bug fixes students. Very often, students believe that when solutions of hydrogen chloride and sulfuric acid react with copper, hydrogen is released. To correct such errors, it is useful to demonstrate the following experience. Pieces of copper are added to test tubes with hydrochloric acid and sulfuric acid solution. Students observe that under normal conditions and when heated, hydrogen is not released.
Adjustment of the process of acquiring experimental skills is facilitated by experiments that demonstrate consequences of incorrect performance of certain chemical operations. For example, how to dilute concentrated sulfuric acid with water. To do this, concentrated sulfuric acid is poured into a tall beaker. The glass is covered with a sheet of filter paper and hot water is poured through a hole in the paper with a pipette. When water comes into contact with acid, vapors form and the solution splashes. When sulfuric acid is added to water and the solution is stirred, dissolution proceeds calmly.
Generalizing function of a chemical experiment allows us to develop prerequisites for constructing various types of empirical generalizations. Using a series of experiments, one can draw a general conclusion, for example, about the belonging of various classes of substances to electrolytes.
Research function of a chemical experiment most clearly manifested in problem-based learning. Let's consider this issue in more detail.
PROBLEM EXPERIMENT
As you know, the starting point of any directed research is a problem. The search for ways to solve a problem leads the researcher to put forward one or another idea - an initial assumption. From the moment the initial assumption is born, the process of hypothesis formation begins. Initial assumptions are born in the form of a guess, i.e. intuitively. Finding an idea for a possible solution to a problem is a deeply creative process, and there is no single solution. However, the initial assumption does not appear out of thin air. It is the result of the researcher studying new factual data based on knowledge accumulated in science. Reinforcing an idea with more and more new arguments leads to the creation of a reasonable assumption - a hypothesis.
There are several ways to confirm the truth of a hypothesis. The main and most common method is to derive the consequences arising from it and verify them, i.e. establishing compliance with actual data and consistency with them. In this case, the reasoning is based on the following scheme: if the main assumption of the hypothesis is true, then in reality such and such specific phenomena should take place. If these phenomena are discovered through targeted observation, in scientific experiments or in practical activities, then the hypothesis will be confirmed. It was in this way that the hypothesis about the existence of ions in solutions was confirmed at one time.
Another way to confirm a hypothesis is to directly detect objects, the idea of the existence of which was the main content of the hypothesis. This method was widely used by D.I. Mendeleev to predict the properties of elements that had not yet been discovered.
And finally, a hypothesis can be confirmed by deductively deducing it from another, but already reliable knowledge - a scientific theory, law. To do this, it is necessary that, with the development of science, a law from which this hypothesis could be deduced should be reliably established. An example is the discovery of compounds of inert gases. Until the 1940s It was believed that inert gases are not capable of forming chemical compounds. The development of theoretical concepts, assessment of the binding energies of electrons in an atom, ionization potentials and ionic radii made it possible to put forward the hypothesis that electronic octets in noble gas atoms are not so stable. In 1933, the American scientist L. Pauling quite convincingly demonstrated the fundamental possibility of the formation of chemical compounds of xenon and krypton with fluorine. But almost 30 years passed before the world's first noble gas compounds Xe(PtF 6) and Kr(PtF 6) were born.
The use of hypotheses in the educational process is not limited to the implementation of the principle of historicism. Great opportunities for using educational hypotheses lie in the organization of the educational process. At the same time, the student himself can be put in the role of a researcher, a generator of ideas.
There is great potential in using a chemical experiment in a lesson. Carrying out standard experiments provided for in the school curriculum does little to stimulate the creative work of students in the classroom and does not fully correspond to the specifics of chemical science itself. It is characterized by an experiment that is exploratory and problematic in nature. It is advisable to include such experiments in conversations of a heuristic nature or in the process of problematic presentation of material.
As an illustration, we can conduct problematic experiments developed by Yu.V. Surin 2 . It is well known that students often make mistakes in writing equations for the reactions of metals with nitric acid, considering the evolution of hydrogen acceptable. This error can be prevented by conducting an experiment included in the problem conversation. When starting to study the issue of the interaction of metals with nitric acid, the teacher first invites students to make assumptions about the possible products of such interaction.
Students often believe that metals release hydrogen not only from solutions of hydrochloric and sulfuric acids, but also from nitric acid. To create a problem situation, the teacher suggests conducting a research experiment and giving an explanation of the results of the experiment.
Several zinc granules are placed in a test tube with hydrochloric acid. After the reaction begins with the release of hydrogen, add 1-2 drops of concentrated nitric acid. Students observe that the evolution of hydrogen practically stops, but after a while it resumes. This result of the experiment seems incomprehensible to students and confuses them. The experiment makes us think about a number of questions:
1. What is the reason for the observed phenomenon?
2. Why does the addition of nitric acid affect the evolution of hydrogen from a solution of hydrochloric acid?
3. Why does the evolution of hydrogen resume after a certain time?
Students make suggestions to explain this unusual fact. They are fully prepared to solve the problem, because... have a sufficient knowledge of the properties of acids and are familiar with drawing up equations for redox reactions. A working hypothesis is put forward: the hydrogen released from hydrochloric acid is spent on the reduction of nitric acid. Students can justify this hypothesis by updating their knowledge about the reducing properties of hydrogen. Remembering that hydrogen at the time of release is a very strong reducing agent, and nitric acid is an oxidizing agent, students write down the equation for the reduction reaction of nitric acid:
HNO 3 + 8H = NH 3 + 3H 2 O.
NH 3 + HCl = NH 4 Cl.
Students can prove that this is indeed the case by testing the solution for the content of ammonium ion. Students can use the conclusion obtained during the research experiment to correctly write the equation for the reaction of zinc with highly dilute nitric acid:
4Zn + 10HNO 3 = 4Zn(NO 3) 2 + NH 4 NO 3 + 3H 2 O.
Now students will be able to answer all the questions posed when identifying a working hypothesis. Hydrogen is not released from nitric acid and solutions of other acids in the presence of nitric acid because it is spent on the reduction of nitric acid. The evolution of hydrogen resumes in this experiment because all the nitric acid is reduced.
The student acts as a researcher when solving experimental problems. Thus, when studying the properties of substances, the research scheme may be as follows:
updating knowledge;
setting research goals;
conducting theoretical analysis;
building a hypothesis;
drawing up a plan for experimental testing of the hypothesis;
performing an experiment;
discussion of the results and formulation of conclusions.
Experiment is the most important way to connect theory with practice when teaching chemistry, a way to transform knowledge into beliefs. A chemical experiment used in school practice usually does not contradict existing laws and serves as confirmation of certain theoretical principles. However, the results of some chemical experiments are unexpected and do not fit into traditional ideas about the properties of substances or the patterns of chemical reactions. For example, is a chemical reaction possible between hydrobromic acid and a metal that is in the electrochemical series of metal voltages after hydrogen? Or: can a weak acid displace a stronger acid from its salt? The answer seems clear - no. Nevertheless, such examples exist and have scientific confirmation. Such experiences are fertile ground for introducing problem-based learning into the educational process and developing the student’s dialectical and systemic thinking.
Let us give a description of several examples of such paradoxical experiments.
Dissolving copper in hydrobromic acid
Reagents. Freshly precipitated copper, strong solution of hydrobromic acid.
Conducting the experiment. Pour into a test tube with a small amount of freshly precipitated copper
3–5 ml of hydrobromic acid and carefully heat on the flame of an alcohol lamp. Vigorous interaction of copper with acid begins. The hydrogen released is collected in a small test tube or directly ignited at the opening of the test tube. Hydrogen burns with a greenish flame.
Obtaining freshly deposited copper. A saturated solution of copper(II) sulfate is poured into a porcelain cup and zinc granules are added. The released copper is deposited on the zinc in the form of a loose mass. When stirring the solution, the precipitate settles at the bottom of the cup. The precipitate is washed, granules of unreacted zinc are removed; The resulting copper, without drying, is used for experiment.
Explanation of experience. The interaction of copper with hydrobromic acid can be explained by the fact that the reaction results in the formation of a complex compound H:
4HBr + 2Cu = 2H + H2.
The complex ion is quite strong, as a result of which the concentration of copper ions Cu + in the solution turns out to be negligible, the electrode potential of copper becomes negative and hydrogen is released.
A similar experiment can be carried out with silver and hydroiodic acid. With silver powder the reaction is very violent. The resulting silver iodide is practically insoluble in water (solubility product PR(AgI) = 8.3 10 –17). Therefore, in this case, the concentration of silver ions in the solution is negligible, and the silver potential becomes negative.
A weak acid displaces a strong acid from its salt
Reagents. Boric acid, sodium chloride, universal indicator or blue litmus paper.
Conducting the experiment. A finely ground mixture consisting of 1 g of sodium chloride and 3 g of boric acid is placed in a test tube. The test tube is secured in the test tube holder and heated on the flame of an alcohol lamp. After some time, white smoke appears at the opening of the test tube. A universal indicator paper moistened with water is brought to the opening of the test tube; reddening of the paper is observed. When conducting an experiment, the teacher must note the non-volatility of boric acid.
Explanation of experience. When the mixture is heated, the following reaction occurs:
2NaCl + 4H 3 BO 3 = Na 2 B 4 O 7 + 5H 2 O + 2HCl.
In solution, the reaction would proceed in the opposite direction - hydrochloric acid would displace boric acid from its salt. When heated, the equilibrium shifts towards the formation of volatile products - hydrogen chloride and water vapor. This also produces heat-resistant sodium tetraborate. The possibility of this chemical process occurring can also be confirmed by thermodynamic calculations.
N/S= 486.6/1 = 486.6 K, or 213.6 °C.This chemical reaction occurs with relatively little heating.
Dissolution of copper in a solution of iron(III) chloride
Reagents. Freshly precipitated copper, 10% iron(III) chloride solution.
Conducting the experiment. A little freshly precipitated copper is placed in a test tube and a solution of iron(III) chloride is added. Within a minute, the copper dissolves and the solution turns green. To increase the reaction rate, the solution can be slightly heated. When using copper filings, shavings or copper wire, the reaction is too slow.
Explanation of experience. This chemical reaction is used in radio engineering for etching circuit boards. In this case, a process occurs described by the following chemical process:
Cu + FeCl 3 = CuCl 2 + FeCl 2.
The reaction is redox. The iron ion Fe 3+ is an oxidizing agent, and the copper atom is a reducing agent. A measure of the redox ability of substances is their redox potential. The greater the algebraic value of the standard redox potential of a given atom or ion, the greater its oxidizing properties, and the smaller the algebraic value of the redox potential of an atom or ion, the greater its reducing properties.
To determine the direction of the redox reaction, it is necessary to find the emf of the element formed from a given oxidizing agent and reducing agent. EMF ( E) redox element is equal to:
E = E(ok-la) – E(vo-la).
If E> 0, then this reaction is possible. Redox potentials of couples E 0 (Fe 3+ /Fe 2+) = 0.771 V, E 0 (Cu 2+ /Cu 0) = 0.338 V. Let’s find the electromotive force of the reaction:
EMF = 0.771 – 0.338 = 0.433 V.
A positive EMF value confirms the possibility of this reaction occurring under standard conditions.
Dissolving copper in ammonia solution
Reagents. 15–25% ammonia solution, freshly deposited copper.
Conducting the experiment. A few grains of freshly precipitated copper are placed in a flask with a volume of 250–300 ml and 15–20 ml of a strong ammonia solution is added. The flask is stoppered and shaken vigorously for several seconds. The solution turns blue.
Explanation of experience. The dissolution of copper in an ammonia solution can be explained by the fact that when copper is oxidized by atmospheric oxygen in the presence of ammonia, a stable complex ion is formed, which determines the direction of the chemical reaction:
2Cu + 8NH 3 + O 2 + 2H 2 O = 2 2+ + 4OH – .
Since the reaction is redox, its emf can be calculated:
Cu + 4NH 3 – 2 e = 2+ , E 0 = –0.07 V,
O2 + 2H2O + 4 e= 4OH – , E 0 = 0.401 V,
EMF = 0.401 – (–0.07) = 0.408 V.
A positive EMF value, as in the previous experiment, indicates the possibility of its occurrence.
An educational chemical experiment is one of the teaching methods, the specificity of which is to reflect an integral component of science. The most important feature of a chemical experiment as a means of cognition is that in the process of observation and when independently performing experiments, students not only communicate with specific objects of chemical science, but can see and carry out processes of qualitative change in substances. Thus, students learn the diverse nature of substances, accumulate facts for comparisons, generalizations, conclusions, and become convinced of the possibility of controlling complex chemical processes.
Questions and tasks for independent work
1. What functions does the experiment perform in the educational process?
Answer. Heuristic, corrective, generalizing and research.
2. What ways to confirm a hypothesis do you know?
Answer. Deriving consequences arising from it and their verification, direct detection of objects, deductive deduction from a scientific theory or law.
3. What is the main didactic disadvantage of laboratory experiments?
Answer. The impossibility of fully developing experimental chemical skills of students.
4. What criteria for selecting a demonstration experiment for a lesson do you use in your practice?
(Various options for answering this question are possible. This is where the teacher’s creative approach to setting up a chemical experiment is manifested.)
1 Zlotnikov E.G.. On the content of the concept of “educational chemical experiment” in the system of intensive training. In the book: Improving the content and methods of teaching chemistry in high school.
L.: LGPI im. A.I. Herzen, 1990.
2 Surin Yu.V.. Methodology for conducting problem experiments in chemistry. Developmental experiment.
M.: Shkola-Press, 1998.
CONTENT
Introduction.
Chapter 1. Chemical experiment in the process of teaching chemistry.
§ 1.1. Chemical experiment as a source of knowledge and a means of education.
.
Chapter 2. Issues of organizing a chemical experiment.
§ 2.1. Preparation of a chemical experiment by a teacher.
§ 2.2. Preparing students to perform a chemical experiment.
§ 2.3. Responsibilities of a laboratory assistant in preparing and conducting a chemical experiment.
Chapter 3. Chemical experiment technique.
§ 3.1. Demonstration technology.
§ 3.2. Performing laboratory experiments.
§ 3.3. Carrying out practical work.
§ 3.4. Solving experimental problems.
§ 3.5. Thought experiment.
§ 3.6. Chemical experiment in problem-based learning.
§ 3.7. Chemical experiment and technical teaching aids.
Chapter 4. Methodology for developing experimental skills and abilities.
§ 4.1. Classification of experimental skills and abilities.
§ 4.2. The role of observation in the process of developing experimental skills.
If you mentally trace the historical path of chemical science, you can be convinced that experiment plays a huge role in its development. All significant theoretical discoveries in chemistry are the result of a generalization of a large number of experimental facts. Knowledge of the nature of substances is achieved through experiment; it helps to reveal the relationships and interdependencies between them.
If experiment is so important in chemical science, then it plays an equally important role when teaching the basics of this science at school. The formation of ideas and concepts about substances and their transformations in a chemistry course, and on the basis of this, theoretical generalizations, is impossible without concrete observation of these substances and without a chemical experiment. At the same time, to explain the essence of observed chemical phenomena and processes occurring during a chemical experiment, students are required to have a deep knowledge of laws and theories. In addition, a chemical experiment plays an important role in developing skills for conducting experiments.
Consequently, only in close interaction between experiment and theory in the educational process can one achieve high quality of students’ knowledge in chemistry.
A chemical experiment should be considered as a process that includes two active parties - the teacher and the student. In this regard, a chemical experiment during training can be considered as a creative activity of a teacher aimed at “equipping” students with a certain system of knowledge, skills and abilities, and as a cognitive activity of students aimed at mastering a system of knowledge, skills and abilities. In the first case, the student acts as an object that is influenced, in the second - as a subject connecting both types of activities. Only in this way is a student able to penetrate into the essence of chemical phenomena and processes, master them at the level of general patterns, leading ideas and theories, and use the acquired knowledge for further knowledge of the subject of chemistry.
Issues of chemical experiments are considered in a number of works on methods of teaching chemistry. But in most cases, they pay attention to the technique of setting up experiments and much less often to the methods of using them in lessons. There are no special manuals specifically devoted to the methodology of a chemical experiment. Hence the main idea of this manual is to show the methodology of a chemical experiment as an integral system and determine its significance in the process of teaching and upbringing in chemistry lessons and in extracurricular activities. From this position, the methodology is considered as an integral part of a chemical experiment, which will help improve the scientific and methodological training of chemistry teachers, and the implementation of its recommendations will help to activate students in the process of teaching chemistry.
The internal relationship between the activities of the teacher and students in the process of a chemical experiment will allow organizing the process of knowledge of chemistry not at the level of descriptive familiarization with phenomena and processes, but at the level of mastering their essence, explaining the cause-and-effect relationships between them from the standpoint of modern chemical science.
The methodological manual does not contain the development of all lessons on the topics, but provides only general recommendations that can be useful to the teacher when preparing and conducting a chemical experiment in the classroom, taking into account the content of the educational material and learning objectives.
A novice teacher in his work can use the recommendations from this manual to successfully master the technique of a chemical experiment. An experienced teacher, comparing his experience with the proposed methodology and showing a creative approach, can think through and improve the methodology for conducting a chemical experiment in his lessons.
Chapter I
Chemical experiment
in the process of teaching chemistry
§ 1.1. Chemical experiment
as a source of knowledge and a means of education
When studying chemistry, chemical experiment plays an important role - an integral part of the educational process.
The experimental nature of chemistry is manifested primarily in the fact that every scientific concept must logically follow from the task at hand and be justified practically. Cognition begins with the sensation and perception of specific objects, phenomena, processes, facts and then proceeds to generalization and abstraction. A chemical concept is generalized knowledge about the essential features of chemical phenomena and processes that are formed on the basis of their perception. Their analysis makes it possible to find the essential features inherent in all of them and, on this basis, to establish chemical laws. Using various types of chemical experiments, the teacher teaches how to concretize theoretical knowledge and find the general in the individual, concrete. A chemical experiment helps students fill the chemical concepts they are learning with living, concrete content and see general patterns in individual facts.
A chemical experiment promotes the development of independence and increases interest in chemistry, because in the process of performing it, students become convinced not only of the practical significance of such work, but also have the opportunity to creatively apply their knowledge.
A chemical experiment develops students' thinking and mental activity; it can be considered as a criterion for the correctness of the results obtained and the conclusions drawn. Very often, an experiment becomes a source of formed ideas, without which productive mental activity cannot take place. In mental development, theory plays a leading role, but in unity with experiment and practice. The experience of chemistry teachers shows that one of the reasons for lagging behind in studies is the difficulty caused by the transition from visual images to abstract concepts. Systematically conducting experiments, during which children train in this skill, can help improve academic performance, in particular in chemistry. Students use the acquired skills and abilities not only for independent and active acquisition of knowledge while studying at a secondary educational institution, but also after graduation during self-education.
A chemical experiment is carried out in several stages:
first
– justification for setting up the experiment,
second
– planning and execution,
third
– evaluation of the results obtained.
It is possible to carry out an experiment only based on previously acquired knowledge. The theoretical justification of experience contributes to its perception, which becomes more focused and active, and comprehension of its essence.
Conducting an experiment usually involves developing a hypothesis. Involving students in this work develops their thinking, forces them to apply existing knowledge to formulate a hypothesis, and as a result of testing it, the children gain new knowledge.
A chemical experiment opens up great opportunities both for creating and solving problem situations, and for testing the correctness of the hypothesis put forward.
Consequently, the experiment has a positive effect on the mental development of students, and the teacher has the opportunity to control the processes of thinking, learning and knowledge acquisition.
Chemistry programs make extensive use of chemistry experimentation—demonstrations, laboratory experiments, practical exercises, and experimental problems—throughout all years of study.
A chemical experiment can perform various didactic functions, be used in various forms and be combined with different methods and means of teaching. It is a system that uses the principle of gradually increasing the independence of students: from demonstrating phenomena through conducting frontal laboratory experiments under the guidance of a teacher to independent work when performing practical exercises and solving experimental problems.
Conducting demonstrations makes it possible to introduce students to various chemical phenomena and the connections between them, the generalization of which can form the basis of a law or theoretical conclusion; with the design and principle of operation of devices and installations; with the essence of the processes occurring in them, which can act as criteria for the correctness of conclusions.
A demonstration experiment is carried out for various purposes, for example, it can serve as the initial stage of mastering a theoretical position. Thus, when considering the conditions on which the degree of dissociation of electrolytes depends, the teacher suggests answering the question: “Does the degree of dissociation depend on the concentration of the solution?” An experience based on testing the electrical conductivity of concentrated and dilute solutions of acetic acid is demonstrated. Comparing the results of the experiment, students come to the conclusion that the degree of dissociation of the electrolyte depends on the concentration of the solution, and establish a pattern - with dilution of the solution, the degree of dissociation increases.
The demonstration experiment illustrates the correctness of the theoretical position stated by the teacher. For example, to prove that when some salts are heated, volatile acids are released, the teacher obtains nitric acid from nitrates and shows its specific properties or, speaking about the chemical properties of metals, shows experiments on the interaction of metals with non-metals and water. In this case, each time the teacher must clearly formulate the purpose of the experiment. His explanations help to analyze the results obtained, highlight the main thing, and establish connections between theoretical principles and experimental data illustrating them.
By performing laboratory experiments and practical work, students independently investigate chemical phenomena and laws and in practice become convinced of their validity, which contributes to the conscious acquisition of knowledge. Sometimes, when conducting these experiments, a creative approach is manifested - the application of knowledge in new conditions. This allows you to repeat, consolidate, deepen, expand and systematize knowledge from different sections of chemistry. In addition, schoolchildren develop experimental skills in handling reagents and equipment. All this helps to improve theoretical knowledge and polytechnic training of students.
By solving experimental problems, students improve their skills and abilities, learn to apply the acquired theoretical knowledge to solve specific problems.
You can also offer children experiments to perform at home. Home experiments and observations are simple experiments performed without teacher supervision. Conducting them teaches you to independently apply the acquired knowledge, skills and abilities.
Observation as a method of cognition is widely used when conducting chemical experiments. Students’ activities become purposeful and take on an active form, provided that the problem is clearly stated and a method for solving it is developed. For example, if the guys are observing the electrolysis of copper(II) sulfate, then the main thing is to monitor the change in color of the salt solution and the appearance of a red coating on one carbon electrode and gas bubbles near the other. Students interpret the results of observations taking into account their existing theoretical knowledge.
When monitoring the implementation of experiments (laboratory and practical classes), as well as during solving experimental problems, all analyzers function. With their help, children can determine the color, smell, taste, density and other properties of the objects under study, by comparing which they learn to identify essential features and learn their nature.
The experiment should become a necessary part of the lesson when studying specific issues. Students must know why to conduct an experiment, what theoretical position it confirms, and what question it will help answer. For example, when explaining the chemical properties of metals, the teacher brings up for discussion the question: “Do all metals interact with water?” After the teacher demonstrates the experiments, the children independently draw a conclusion: metals located in the voltage series to the right of hydrogen do not interact with water.
It is very important to analyze the results of experiments in order to obtain a clear answer to the question posed at the beginning of the experiment, to establish all the reasons and conditions that led to the receipt of these results. In addition, a properly organized experiment fosters conscious discipline, develops creative initiative, and respect for property.
The working environment in the laboratory and the exemplary order in it also have an educational effect on students and improve discipline. The laboratory must be constantly kept clean, there must be a strictly thought-out system for storing equipment and reagents: solids - in cabinets according to groups of the periodic table; solutions - according to the main classes of compounds or according to cations or anions; organic substances - also by main classes of compounds or functional groups. Dishes and equipment are neatly arranged in cupboards.
Preliminary preparation of theoretical material for the upcoming practical work increases interest in the latter, which means that the children will be active and disciplined during the lesson. A meaningful understanding of the essence of the experiments, as well as careful execution of the completed work, have a positive effect on the behavior of students during the experiments.
It is necessary to ensure that all students complete practical work and obtain the desired results, so that they feel confident in their abilities and strive to overcome difficulties.
It is very important to provide differentiated assistance: carefully monitor the work of each person, note how he plans and organizes his work, how he masters the skills and techniques of conducting an experiment, whether he can observe, explain the essence of the phenomena occurring, and draw correct conclusions and generalizations. It is necessary that each student independently comprehend the material, use theoretical knowledge to explain ongoing phenomena and processes, draw conclusions and generalizations. When performing experiments, careful use of reagents and materials should be required, and the significance of their savings for the educational institution and the state should be explained.
Particular attention is paid to the technique of performing the work: how to dissolve substances, heat the solution in a test tube or flask, add indicator solutions, etc.
The safety regulations must be posted in a conspicuous place. This teaches you to be organized and disciplined during classes.
The systematic use of experiments in chemistry lessons helps combat formalism in knowledge, develops the ability to observe facts and phenomena and explain their essence in the light of studied theories and laws; forms and improves experimental skills and abilities; instills skills to plan their work and exercise self-control; fosters respect and love for work. This work contributes to general education, comprehensive personal development, and prepares for activities in modern production.
§ 1.2. Types of chemical experiment
Chemical experiment is important in studying chemistry. There are educational demonstration experiment, performed primarily by the teacher on a demonstration table, and student experiment– practical work, laboratory experiments and experimental tasks that students carry out at their workplaces. A unique type of experiment is a thought experiment.
Demonstration experiment
is carried out mainly when presenting new material to create in schoolchildren specific ideas about substances, chemical phenomena and processes, and then to form chemical concepts. It allows you to make clear important conclusions or generalizations from the field of chemistry in a short period of time, teach you how to perform laboratory experiments and individual techniques and operations.
Students' attention is directed to performing the experiment and studying its results. They will not passively observe the conduct of experiments and perceive the material presented if the teacher, demonstrating the experiment, accompanies it with explanations. Thus, he focuses attention on experience and teaches him to observe the phenomenon in all its details. In this case, all the teacher’s techniques and actions are perceived not as magical manipulations, but as a necessity, without which it is almost impossible to complete the experiment. During demonstration experiments, compared to laboratory experiments, observations of phenomena take place in a more organized manner. But demonstrations do not develop the necessary experimental skills and abilities, and therefore must be supplemented by laboratory experiments, practical work and experimental tasks.
The demonstration experiment is carried out in the following cases:
it is impossible to provide the required amount of equipment at the disposal of students;
the experiment is complex and cannot be carried out by schoolchildren themselves;
students do not have the necessary equipment to conduct this experiment;
experiments with small amounts of substances or on a small scale do not give the desired result;
experiments are dangerous (working with alkali metals, using high voltage electric current, etc.);
It is necessary to increase the pace of work in the lesson.
Naturally, each demonstration experience has its own characteristics depending on the nature of the phenomenon being studied and the specific educational task. At the same time, the chemical demonstration experiment must meet the following requirements:
The pedagogical effectiveness of a demonstration experiment, its influence on knowledge and experimental skills depend on the experimental technique. This refers to a set of instruments and devices specially created and used in a demonstration experiment. The teacher should study the classroom equipment as a whole and each device separately, and practice demonstration techniques. The latter is a set of techniques for handling instruments and apparatus in the process of preparing and conducting demonstrations, which ensure their success and expressiveness. Demonstration methodology is a set of techniques that ensure the effectiveness of the demonstration and its best perception. The methodology and demonstration technique are closely related and can be called the technology of demonstration experiment.
When conducting demonstration experiments, a preliminary check of each experiment is very important in terms of technique, quality of reagents, good visibility by students of instruments and the phenomena occurring in them, and guarantees of safety. Sometimes it is advisable to display two devices on a demonstration table: one – assembled and ready for use, the other – disassembled, so that, using it, it is better to explain the structure of the device, for example, a Kipp apparatus, a refrigerator, etc.
You must always remember that any experiment that fails during demonstration undermines the authority of the teacher.
Laboratory experiments
– a type of independent work that involves performing chemical experiments at any stage of the lesson for more productive learning of the material and obtaining specific, conscious and lasting knowledge. In addition, during laboratory experiments, experimental skills are improved, since students work mainly independently. Performing experiments does not take up the entire lesson, but only part of it.
Laboratory experiments are most often carried out to get acquainted with the physical and chemical properties of substances, as well as to clarify theoretical concepts or provisions, and less often to obtain new knowledge. The latter always contain a certain cognitive task that students must solve experimentally. This introduces an element of research that activates the mental activity of schoolchildren.
Laboratory experiments, unlike practical work, introduce a small number of facts. In addition, they do not fully capture the attention of students, like practical exercises, because after a short period of time independently completing the work (experience), students must again be ready to perceive the teacher’s explanation.
Laboratory experiments accompany the presentation of educational material by the teacher and, just like demonstrations, create in students visual representations of the properties of substances and chemical processes, and teach them to generalize observed phenomena. But unlike demonstration experiments, they also develop experimental skills. However, not every experiment can be carried out as a laboratory one (for example, ammonia synthesis, etc.). And not every laboratory experiment is more effective than a demonstration one - many laboratory experiments require more time, and the duration directly depends on the quality of the developed experimental skills. The purpose of laboratory experiments is to acquaint students with the specific phenomenon (substance) being studied as quickly as possible. The technique used is reduced to students performing 2-3 operations, which naturally limits the possibilities of developing practical skills.
The preparation of laboratory experiments should be carried out more carefully than demonstration ones. This is due to the fact that any negligence and omission can lead to a violation of the discipline of the entire class.
We must strive to ensure that each student performs laboratory work individually. As a last resort, you can allow no more than two people to have one set of equipment. This contributes to better organization and activity of children, as well as to the achievement of the goal of laboratory work.
After completing the experiments, they should be analyzed and a brief record of the work done should be made.
Practical work
– a type of independent work when students perform chemical experiments in a specific lesson after studying a topic or section of a chemistry course. It helps to consolidate acquired knowledge and develop the ability to apply this knowledge, as well as the formation and improvement of experimental skills.
Practical work requires students to be more independent than laboratory experiments. This is due to the fact that the children are invited to get acquainted at home with the content of the work and the order of their implementation, and repeat theoretical material that is directly related to the work. The student performs practical work independently, which helps to increase discipline, composure and responsibility. And only in some cases, if there is a lack of equipment, can you be allowed to work in groups of two people, but preferably no more.
The role of the teacher in practical work is to monitor the correct execution of experiments and safety rules, the order on the work table, and the provision of individually differentiated assistance.
During practical work, students write down the results of experiments, and at the end of the lesson they draw appropriate conclusions and generalizations.
§ 1.2. Types of chemical experiment
(continuation)
Experimental tasks
- a type of independent work that contains only a task, and students determine the choice of solution and conduct an experiment independently. This requires from them not only the active application of theoretical knowledge, but also the ability to perform relevant experiments. The main goals of experimental tasks are systematic exercises related to the application of knowledge in practice, as well as the development of experimental skills necessary for various studies.
In contrast to practical classes and laboratory experiments, experimental problems can be solved in every lesson throughout all years of chemistry education when studying and consolidating new material, monitoring students’ knowledge and at home. They can be done individually, in separate groups, or by all students at the same time. By solving experimental problems, schoolchildren not only improve previously acquired skills and abilities, but also learn to apply the acquired knowledge. This facilitates independent finding of a theoretical solution to the problem with mandatory experimental verification of the correctness of the result obtained.
Compared to computational problems, experimental problems are more cognitively valuable. This is explained by the fact that to solve such problems, a correct theoretical justification is not enough - you still need to carry out an experiment and explain its essence. Solving experimental problems allows the teacher to assess in a very short time how much the material has been mastered and how the student knows how to apply the acquired knowledge in practice. Discussion of the results makes it possible to detect errors or shortcomings in the solution, establish their causes, achieve their correction, provide students with differentiated assistance and outline ways to improve experimental skills.
According to their content, experimental tasks are divided into the following.
Tasks on observing physical and chemical phenomena and the ability to explain their essence. For example: “How can you determine from the physical and chemical properties of polyethylene and polystyrene which of the test tubes contains pieces of these plastics? Explain the essence of the observed phenomena."
Tasks on the implementation of the synthesis of substances and the ability to explain or anticipate the conditions for reactions. For example: “From the reagents available on the table - copper(II) oxide, water, copper(II) chloride, solutions of sodium hydroxide and hydrochloric acid - obtain copper(II) hydroxide in two ways. In each case, indicate the reaction conditions.”
Tasks on recognizing substances and the ability to explain their characteristic properties. For example: “Using characteristic reactions, determine which test tube contains glucose and starch. List their characteristic properties."
Tasks to confirm the qualitative composition of substances and the ability to characterize their properties. For example: “Use characteristic reactions to establish that this substance is aluminum chloride. List its characteristic chemical properties.”
Tasks to determine impurities in a given product and the ability to explain the reason for the chosen method of determining mixtures. For example: “Prove that copper sulfate contains sodium chloride impurities. Explain why the method you have chosen to determine the impurity is the most rational.”
Tasks on isolating a substance in its pure form from a mixture and the ability to explain the reason for the chosen method of separating mixtures. For example: “Isolate table salt in its pure form from a mixture containing iron(III) hydroxide and pieces of polyethylene. Explain why the method you chose to separate substances is correct.”
Tasks to consolidate the classification of substances and the ability to define them. For example: “Prove that aminoacetic acid is an amino acid. Define this class of substances."
Tasks on carrying out characteristic reactions and the ability to explain their typical properties. For example: “Identify glucose using characteristic reactions. List its typical chemical properties."
Tasks on preparing solutions of substances with different mass fractions and the ability to explain their preparation. For example: “Prepare 300 g of sodium bicarbonate solution, the mass fraction of which is 0.03, or 3%. Explain why you should first dissolve a substance and then add solvent to a certain mark. Why can’t you do it the other way around?”
Combined tasks that require in-depth knowledge and strong skills to perform.
Experimental tasks distinguish quality And computational and experimental. Qualitative problems are solved empirically; they lack quantitative data and, therefore, mathematical calculations, for example: “Prove experimentally the presence of sulfate ion in iron(III) sulfate.” To solve computational and experimental problems, in addition to setting up the experiment, it is necessary to process certain experimentally obtained data. It is proposed, for example, to obtain a precipitate of iron(III) hydroxide and, based on the resulting mass of the precipitate, calculate the mass of the solution for its preparation with a mass fraction of potassium hydroxide of 0.1 (10%).
The highest form of computational and experimental problems is computational-experimental, which combines the best qualities of both problems.
Thought experiment
as a method of activating students’ cognitive activity, it has been unfairly forgotten, and chemistry teachers practically do not use it. This is most likely due to the lack of information about it in the numerous and varied methodological literature on chemistry and in the training of future chemistry teachers at universities. As a result, it turned out that the thought experiment, which contains great opportunities for developing students’ abstract thinking, does not find its proper application in the practice of teaching chemistry.
This situation could be to some extent justified and tolerable when a real chemical experiment was carried out constantly throughout all the years of studying chemistry at school. Currently, as a result of the current unfavorable social conditions, when a real chemical experiment is very expensive, and many reagents, equipment and accessories are missing and it is used less and less, or even not carried out at all, the question arises about the need to more widely use thought experiments as an alternative real.
A thought experiment costs nothing from a financial point of view; all it takes is a student's head to think. Since the thought experiment is carried out theoretically, it requires very little time. During this short period, active mental activity occurs: the goal of the experiment is set, a problem is created, a hypothesis is put forward, and ways to find and solve the problem are determined. In the absence of reagents and equipment, students theoretically discuss the progress of the experiment and its results and draw conclusions.
The role of the teacher when conducting a thought experiment is very important. He carefully monitors the correctness of the students’ reasoning and acts as an arbiter, assessing the possibility of implementing the student’s proposed way of completing the experiment and obtaining the final result.
In cases where the chemistry classroom has everything necessary to conduct an experiment, the students test their theoretical assumptions practically.
Thus, a thought experiment can be carried out in its pure form, that is, without experiments, and in close unity with a real experiment. In both cases, a thought experiment activates the cognitive activity of students and in every possible way deserves to be in the collection of methods that the teacher uses in his work.
Chapter 2
Organization issues
chemical experiment
The quality and effectiveness of a chemical experiment depend on the preparation and organization of it by the teacher, the preparedness of students and the assistance of a laboratory assistant.
§ 2.1.
Chemical preparation
experiment by teacher
The need for the teacher to prepare an experiment is determined by the educational tasks that are presented to the experiment by the content of the subject of chemistry and the methodology of its teaching.
The effectiveness of chemistry teaching is closely related to the overall planning of educational material. The main tasks that are solved during the planning process are optimizing the educational process, determining the volume of educational material, selecting tasks for the lesson and for home; allocating time to conduct laboratory experiments and practical classes, solving experimental and computational problems; control of knowledge, skills and abilities of students; consolidation and repetition of material.
A chemistry teacher must be able to plan an experiment on the entire topic and for a specific lesson, apply it methodically correctly, select experimental options, guide the cognitive activity of students, analyze and evaluate their own activities during demonstrations and the activities of students when they independently perform experimental work.
A chemical experiment is planned. To do this, at the beginning of the academic year, in a long-term plan, in accordance with the curriculum, the sequence of demonstrations, laboratory experiments, practical exercises and solving experimental problems on topics and their connection with theoretical classes is established; a list of experimental skills and abilities that students must acquire, and didactic means to achieve their goals are determined; extracurricular types of chemical experiments are established that have a professional orientation and significance for extracurricular activities.
Before starting to study the topic, a thorough and detailed analysis of the educational material is carried out to clearly determine, firstly, the amount of knowledge that the teacher himself should possess, and, secondly, the types of experiment that allow the best possible formation and improvement of skills in each lesson when studying this topic.
promising And thematic planning together is necessary for the most rational and timely preparation for these classes.
Knowing in advance the timing of the experiment, the teacher has the opportunity to prepare equipment, teaching aids, etc. for lessons in advance.
Preparation for a lesson depends on the type of lesson and the didactic goal set. First, the teacher clarifies the educational objectives of the lesson and thinks over the methodology for its implementation. In order for a chemical experiment to provide solid and deep knowledge, it is necessary to foresee what experimental skills and abilities will be acquired by students, with the help of what techniques can be used to achieve their understanding of the observed chemical transformations. The teacher is recommended to review the relevant methodological literature, outline questions that will help identify students’ theoretical knowledge on the topic, and highlight points that should be focused on, since they contribute to the acquisition of skills and abilities and facilitate the perception of educational material in the future.
The teacher needs to think about at what stage of the lesson, in what sequence, with what reagents and instruments to conduct the experiments, determine their place during the lesson depending on the significance of the tasks, as well as the form for recording the results obtained (figure, table, reaction equation, etc.). d.).
Before the lesson, it is very important to rehearse the technique for performing each demonstration experiment, check the availability and quality of reagents, and also make sure that the operation of the device and the phenomena occurring are clear, since problems discovered during the lesson affect not only the students’ discipline, but also achieving the set goal. If necessary, reagents should be replaced, instruments adjusted, or other suitable equipment used.
For example, to burn ethylene, acetylene and other gases, it is not necessary to have a straight gas outlet pipe with an extended end. You can use a gas outlet tube at a right angle, keeping in mind that the flow of gases in this case will be sufficient to maintain uniform combustion of gases. Lime water, which becomes unusable due to improper or long-term storage, can be completely replaced with barite water (Ba(OH) 2 solution), the properties of which do not undergo any changes even after long-term storage. If for some reason there is no phenolphthalein in the office, then it can be replaced with purgen (a laxative), which contains phenolphthalein and sugar. Purgen acts similarly to pure phenolphthalein. Instead of silver nitrate, you can use lapis, etc.
In other cases, missing reagents can be obtained in various ways from substances available in the office. It is recommended to involve students for this type of work. This helps the teacher and develops students’ interest in a more in-depth study of chemistry.
When preparing for an experiment, it is also recommended to use cards on which all the necessary data about the experiment is entered: the names of devices, reagents, and accessories are marked on one side, and a drawing of the device and installation diagram are marked on the other. To better preserve and extend the life of the cards, you can place them in a cellophane envelope or print them on two pages of notebook paper and then stick them on cardboard or thick paper.
These cards are intended for a laboratory assistant preparing an experiment (demonstrations, laboratory experiments, practical exercises and experimental problems), and the teacher checks his work.
In some cases, it is advisable to have two identical devices, one of which, disassembled, is used to explain its structure, and the other, assembled, is used to demonstrate it in action.
It is also necessary to show students the physical state of the substances from which their solutions are prepared. This applies to such commonly used substances as sodium hydroxide, calcium hydroxide, indicators, barium chloride, etc. Such repeated comparison enables students to remember that all bases and salts under normal conditions are solids. But in everyday practice they are more often used in the form of solutions of a certain concentration.
The devices that were shown during the demonstration are not disassembled, but are used when questioning students in subsequent lessons.
The study of the physical properties of simple substances and the most important compounds of elements presupposes familiarity with their most important characteristics. To do this, the teacher needs to have sets of handouts for each table. Samples of substances with names and indicated composition are placed in cardboard boxes, they are distributed during the lesson, when it is necessary to familiarize students with them, and immediately after that they are removed. Liquid or solid substances in the form of crystals (or powder), respectively, are poured or poured into jars, flasks or test tubes and in this form are given to students to become familiar with their external characteristics.
For surveys on topics such as “Nitrogen and Phosphorus”, “Carbon and Silicon”, “Metals” and others, it is good to have thematic collections of samples of substances and minerals without their names inscribed.
It is necessary to familiarize students in advance with the list of names of practical work that they will perform in subsequent lessons, so that the children can prepare in advance. In the lesson preceding the practical lesson, the teacher informs the topic, purpose and content of the work, and indicates pages in the textbook for repetition of theoretical material. Students at home carefully read the instructions for the lesson, think through the progress of the work and report on its implementation. In case of any difficulties, it is recommended to refer to the text of the textbook or notes in the notebook.
Before completing the work, the teacher invites students to carefully read its contents again and repeat the progress.
During the conversation, the teacher first checks the degree of preparation for the practical lesson: how theoretically the experiment makes sense. He clarifies the purpose and content of the work to be done, the order in which its individual elements are performed, safety precautions, and the form and content of the report.
Students are given the opportunity to carry out experiments on their own, and the teacher only observes the progress of the work and intervenes if the student makes a serious mistake or fails to complete the task. When walking around students (primarily low-achieving students) in the classroom, the teacher gives the necessary instructions. But help should be provided in such a form that students learn to overcome difficulties on their own, analyze their mistakes, correct them, and show initiative.
Written reports drawn up during the work must contain a drawing of the device, recordings of observations, explanations of the results, answers to questions, instructions, and conclusions.
If the work is small in volume or students have a stable skill in preparing a report, then it is necessary to require the preparation of a report in this lesson. In cases where students do not have time to complete a progress report, they may be allowed to submit rough notes. The teacher checks and signs these notes and returns them to the students for final registration at home during the next lesson. Writing a report at home should be permitted in exceptional cases and only for selected students.
Summing up the results of practical exercises should be carried out in the next lesson. The best works are read out (in part or in full), typical errors are analyzed, the best drawings are shown through an epidiascope, some students are interviewed orally, etc.
A chemistry teacher in secondary schools is faced with the need to independently compile the content of experimental problems on the topics of a chemistry course, and in evening secondary schools also with production content. This is due to the fact that there are no such problems in textbooks, and also because workers of various professions are trained in evening secondary schools.
When selecting experimental tasks, the teacher must comply with the following requirements:
tasks must cover all educational material for the chemistry course;
the content of the tasks should take into account the different levels of students’ preparation and the individual characteristics of their development;
tasks should contribute not only to improving the quality of knowledge in chemistry and improving experimental skills, but also to improving the professional training of workers;
the time allocated for solving problems must be strictly limited;
the conditions of the tasks must be clearly formulated.
Exam papers in chemistry must include laboratory experiments and experimental tasks, the purpose of which is to test the presence of experimental skills of students.
Examples of experiments and tasks for each ticket are prepared by the teacher.
The effectiveness of conducting lessons with a chemical experiment largely depends on how modern requirements of the scientific organization of work (SLO), ergonomics, safety precautions and aesthetics are taken into account when equipping the teacher’s workplace.
The teacher of chemistry, who is also the head of the chemical laboratory, is responsible for organizing all the work to equip his office with new equipment and devices. Under his leadership, a list of the necessary equipment and inventory for the current and subsequent years is compiled. To eliminate equipment malfunctions and produce new manuals in the classroom, it is advisable to create a circle and involve students in participating in its work.
§ 2.2.
Preparing students to perform
chemical experiment
The correct and quick implementation of practical work in the classroom to a large extent depends on the good preparation of students and the organization of classes.
The preparation of students involves doing homework that precedes the practical lesson, namely: repetition of the relevant theoretical material from the textbook, familiarization with the content of the experimental work in order to know what practical skills and abilities will be necessary for its implementation.
For example, to complete the practical work “Preparation of ethylene and experiments with it,” students repeat material about the structure of the molecule, production, physical and chemical properties of ethylene, paying special attention to the dependence of these properties on the structure of the molecule; get acquainted with the picture, which shows a device for producing ethylene; remember how to properly assemble, check for leaks and strengthen the device for producing gases; repeat what precautions must be taken when working with starting substances.
To maintain correct posture and good vision, students must be provided with comfortable workplaces in accordance with the requirements of the scientific organization of labor (SLO) and ergonomics. The equipment must be made taking into account the anthropometric characteristics of students and the nature of work activity. Workstations are equipped with the necessary equipment and reagents and are assigned to students for a certain period of time. They are required to maintain order on the table while doing work and after it is completed.
During the experiment, students, following the instructions, carefully observe the signs and conditions of the reactions and record all the changes that occur in their notebooks.
Reports on practical exercises are prepared in separate notebooks. Reports are compiled approximately according to the following scheme: name and date of work; list of instruments and equipment; description of the progress of work (assembly of the device, reagents, observations, explanation of results, etc.); diagrams and drawings reflecting the essence of the observed phenomena; generalization and conclusions; short answers to the questions posed in the assignment.
It is advisable that the report be submitted on the day of the practical work. Writing a report teaches students to analyze their actions, make generalizations and conclusions.
After the practical lesson, the equipment is removed, which is controlled by the laboratory assistant: each student collects from the table and puts on a tray (or cuvette) all the individual objects and reagents and takes them to the laboratory room. The attendants check the cleanliness of student tables. All this is done quickly and does not interfere with the next lesson. Then the laboratory assistant and students disassemble the trays, wash test tubes and other utensils, and place laboratory supplies and reagents in their permanent places (in cabinets and on shelves).
Conducting experiments in practical classes requires composure, precision and accuracy. If you are poorly prepared for the work or perform it carelessly, the experiments may not work out. During the work itself, students become convinced that successful implementation of experiments is possible only with a deep understanding of the material studied and the ability to apply theoretical knowledge in practice.
As a rule, in practical classes, students repeat experiments that the teacher has already demonstrated when studying a given topic. But, observing these experiments from a distance, the guys cannot always understand the details. After theoretical training, they have the opportunity to repeat the experiments on their own, delve into all the details of the experiments and explain their essence. This creates interest in the work, and knowledge, supported by practical work, becomes more durable and effective.
As they acquire knowledge and experimental skills, children should be given more independence in conducting chemical experiments in practical classes. You can offer to independently analyze the experimental technique, draw up a work plan, conduct observations and explain the results obtained. This method of performing experiments is close to solving experimental problems, which in a practical lesson should also be preceded by careful home preparation. The course of solving problems is thought through, a plan for conducting relevant experiments is developed, and a list of necessary reagents, materials, utensils and accessories is compiled. This allows students to come to the laboratory and immediately begin performing the experiment. Experimental tasks are performed without instructions, so they require significantly more independence from students.
Not all students finish practical work at the same time, which is understandable. Everyone has their own skills, individual characteristics, their own level of preparedness, and hence the unequal pace of work. Some do not meet the allotted time, others finish work ahead of schedule. For those who cope with the task earlier, you can offer task cards with the content of new experiences. This helps maintain a working environment in the classroom and stimulates students' thinking.
Unlike practical classes, laboratory experiments are performed by all the children under the guidance of a teacher; this contributes to a conscious and specific understanding of the new educational material. They are given little time, so students need attention, diligence and discipline. Experiments are performed according to the oral instructions of the teacher or according to task cards, the content of which can be projected onto the screen using an epidiascope or codoscope.
On a special stand, you should indicate what general skills and abilities students should master while studying the course of inorganic and organic chemistry. On separate examples it is possible to demonstrate the value of any acquired specific skill.
For example, what you need to know when working with a gas burner. Natural gas is poisonous, so releasing it indoors is unacceptable; when the burner is not in use, the taps must be closed; the greatest amount of heat is released during the formation of a non-luminous flame. When igniting a gas burner, the following procedure should be followed: connect the burner with a rubber tube to the tap; close the air access using a disk or clip; ignite the gas a few seconds after it starts; adjust the air supply so that the flame becomes non-luminous; in the process of work, make sure that there is no "overshoot" of the flame - the gas ignites in the lower part of the tube and burns inside it, and not in the upper part of the tube; if a “slip” is detected, the burner must be immediately extinguished, allowed to cool and re-ignited with the blower closed.
It is recommended to indicate literature on this topic at the same stand.
It is very good to keep records in the classroom of the development of experimental skills and abilities by year of study, which serves as a kind of control and self-control. Accounting consists of a list of developed and practiced skills and abilities of each student in inorganic and organic chemistry.
During the exam, the student occupies one of five tables, which are equipped specifically for performing laboratory experiments and solving experimental problems. At this table, he prepares answers to the theoretical questions on the ticket and plans the sequence of the experiment. First, the student writes down the equation of a chemical reaction, then makes a list of the reagents and equipment that he intends to use in a given experiment or experimental task, and also, if necessary, makes a drawing or diagram. Only after the teacher has checked the notes does the student begin to perform the experiment.
When assessing the performance of laboratory experiments and solving experimental problems, they take into account the ability to test devices for leaks, assemble them and strengthen them in a laboratory stand, use reagents and equipment, use reagents economically, consistently perform operations when recognizing or obtaining substances, observe safety precautions, etc.
Students who already have well-developed work skills should be involved in the work of equipping the classroom. They can produce the missing tables on the production of substances, installation diagrams, drawings of devices, operating installations and instruments, collections, and also take part in collecting jars and bottles. Parents and children who graduated from this school can provide great assistance in this work.
§ 3.3. Carrying out practical work
The approximate timing of practical work is determined according to the thematic plan.
In the lesson plan, the teacher outlines how he will observe and control the work of the entire class and individual students, what technical and theoretical difficulties the children may encounter when performing experiments, and what differentiated assistance they need to provide to successfully complete and complete the work.
The plan also records the possible replacement of reagents or equipment, changes in the content of any experiment, lists questions on which students’ theoretical preparedness for the lesson will be tested, and also provides instructions on the technique of performing experiments.
Practical skills are successfully developed if schoolchildren already have sufficient theoretical knowledge. In this case, individual operations are performed more meaningfully and strong skills are acquired. Therefore, the teacher first of all needs to check the theoretical preparation of students for the upcoming work. For this purpose, questions are proposed with the help of which the teacher controls the strength and depth of knowledge and at the same time activates mental activity.
Questions, naturally, should follow from the content of the practical work itself. If any changes in the work are planned, this will also be announced at the very beginning of the lesson. Then the teacher answers questions that arose while preparing for the lesson at home, explains and shows the techniques that will be used for the first time. Less time is devoted to explaining the techniques for carrying out already known operations and techniques, which the children are once again familiar with according to the instructions for practical work. But much more time is devoted to monitoring the implementation of these operations during work.
After this, students carry out experiments, and the teacher monitors the quality of their implementation and, if there are difficulties, provides differentiated assistance. If an error is discovered, there is no need to rush to correct it; the student must be given the opportunity to think and do it on their own.
If the chemistry laboratory is equipped with everything necessary for an experiment, then during practical classes each student performs experiments independently. If such conditions are absent, then the practical work is performed by two students in turn: each conducts approximately half of the intended experiments. But even if schoolchildren perform experiments in pairs, each student submits a report on the work done separately. This forces them to delve into the essence of the work being carried out by their comrade, observe, and draw conclusions.
When conducting experiments, you should ensure that each student is an active performer, and not a passive contemplator. Only under this condition are experimental skills consolidated and improved.
The teacher records his observations in a notebook where the names of students, elements of operations, as well as skills and abilities that are acquired or improved in this lesson are recorded. Some comments are briefly recorded in the “Notes” column.
For example, during practical work on the topic “Recognition of polymeric materials - plastics, chemical fibers,” the teacher monitors the correct development of the following experimental skills:
light and extinguish burners (alcohol lamps);
identify plastics and fibers by appearance;
determine the density of plastic;
identify plastics and fibers by their combustion patterns;
use crucible tongs;
work with lookup tables.
As the students complete their experiments, they record their results in notebooks and then compile a written report. In any form of report, it should contain a brief record of observations, their explanation and conclusions. Students think through the order of performing experiments at home in preparation for class, so they spend significantly less time on writing a report during practical work. You should not transfer the preparation of reports to home, as this discourages students in class. In addition, the results obtained during observation are quickly forgotten, which leads to cheating.
Student laboratory assistants provide great assistance in preparing practical work. They help display and put away all the sets on trays. These students can be called upon to observe the work of their comrades and help them when difficulties arise. To ensure success, it is advisable to give these students the opportunity to complete practical work in advance and provide them with a list of questions on which they should conduct observations.
Students' performance in practical work is assessed on the basis of a written report and observation results. Such criteria could be:
error-free and accurate execution of experiments;
correct recording of explanations, conclusions and reaction equations;
skillful handling of reagents and equipment;
quality of report design;
compliance with safety precautions and discipline during classes.
Typical mistakes made when performing experiments are discussed in the next lesson. Individual students are invited to carry out some practical experiments at the demonstration table. The whole class participates in discussing their results.
Practical work carried out according to textbook instructions limits the independence of students, since the content of these works involves mainly executive activity. Issues related to the development of students' thinking should be resolved on the basis of their increasing independence in carrying out this work. A lot can be done in this direction without changing the topics and the amount of practical work provided for in the program.
Let's take a practical example as an example. on the topic “Determination of mineral fertilizers”, the implementation of which requires great activity and independence.
Research objectives.
1. Using characteristic reactions, determine ammonium nitrate, sodium nitrate and potassium salt located under numbers in test tubes (in bags).
2. Prove that the composition of ammonium nitrate includes ammonium ions and nitrate ions of sodium nitrate - sodium ions Na + and nitrate ions, potassium salt - potassium ions K + and
chloride ions Cl – .
Research plan.
1. Consider the appearance of the fertilizer.
2. Check the solubility of fertilizers in water.
3. Pour a concentrated solution of sulfuric acid into test tubes with solid fertilizers, lower the pieces of copper ( for what purpose?) and warm up slightly ( Why?).
4. Pour into test tubes with fertilizer solutions:
a) a solution of barium chloride and acetic acid ( For what?);
b) alkali solution ( for what purpose?) and heat ( Why?);
c) silver nitrate solution ( For what?).
5. Apply fertilizer crystals ( How?) into the flame of a burner or alcohol lamp ( for what purpose?).
6. Carefully observe the phenomena occurring.
7. Write down reaction equations.
8. Note the characteristic coloring of the flame of a burner or alcohol lamp when applying fertilizers to it.
9. Draw appropriate conclusions.
Questions to check.
1. How to determine the ions Na + , K + , , , Cl – ?
2. Is it possible to distinguish Na + and ions by the color of the flame? Why? How should they be defined?
3. For what purpose is concentrated sulfuric acid added to fertilizers simultaneously with pieces of copper? Give a reasoned answer.
4. Why is acetic acid added along with barium chloride?
5. How can we explain that many fertilizers turn the flame yellow?
6. How can we explain the unequal degree of heating of fertilizers with concentrated sulfuric acid and copper, as well as with sodium hydroxide solution?
7. How else can you determine the nitrate ion in alkali metal salts?
Determining the objectives of the experiment and drawing up a research plan helps students focus on the most important thing during experiments. With the help of test questions for practical work, they find out the degree of their understanding of the essence of phenomena and processes, as well as the ability to apply the acquired knowledge in new situations.
The teacher can, by analogy, independently compose the content of other practical works.
At the final lessons, practical work of new content is not carried out. However, it is advisable to devote the last two lessons only to a chemical experiment. On one of them, students obtain gases known to them (oxygen, ammonia, carbon monoxide (IV), hydrogen, ethylene, etc.) and prove their presence, on the other, they solve experimental problems to recognize inorganic and organic substances. Despite the fact that students have performed these experiments before, they are repeated on a new and higher quality basis. This is expressed not only in the ability to quickly and independently conduct experiments, but also in greater demands on evaluating the results of work.
The quality and strength of acquired skills and abilities depend on the frequency of their use in practical work. The fact that some skills and abilities are used during training only once or twice, and then with a long break, does not exclude the fact that students, if necessary, will apply and improve them in their work activities.
Chapter 4. Methodology for developing experimental skills and abilities
§ 4.1. Classification of experimental skills and abilities
The unity of theory and practice, as is known, most contributes to the solid assimilation of educational material, therefore theoretical knowledge in chemistry should be based on experiment, and a chemical experiment should involve the application of theoretical knowledge. In the learning process, both of these links must be in close relationship, and neither of them can be belittled or exalted.Experimental skills and abilities must be developed systematically by performing laboratory experiments, conducting practical classes and solving experimental problems. The success of this work largely depends on the teacher’s knowledge of the structure and content of experimental skills, as well as on the conditions for the effective use of various types of educational chemical experiments.
According to the form of student activity, the experimental skills that are formed in the process of teaching chemistry can be divided into five groups:
organizational;
technical;
measuring;
intellectual;
design.
Based on the chemistry curriculum, it is possible to establish the content of skills and abilities for each of these groups.
Organizational skills:
1) planning the experiment;
2) selection of reagents and equipment;
3) rational use of time, means, methods and techniques in the process of performing work;
4) exercising self-control;
5) keeping the workplace clean and tidy;
6) independence in work.
Technical skills:
1) handling of reagents and equipment;
2) assembly of devices and installations from finished parts and assemblies;
3) performing chemical operations;
4) compliance with labor safety rules.
Measuring skills:
1) measuring volumes of liquids and gases;
2) weighing;
3) measurements of temperature and density of liquids;
4) processing of measurement results.
Intellectual skills:
1) clarifying the purpose and defining the objectives of the experiment;
2) putting forward a hypothesis;
3) use of existing knowledge;
4) description of observed phenomena and processes;
5) analysis of the experimental results;
6) establishing cause-and-effect relationships;
7) generalization and conclusions.
Design skills:
1) repair of equipment, instruments and installations;
2) improvement of equipment, instruments and installations;
3) manufacture of equipment, instruments and installations;
4) graphic design (in the form of drawings and diagrams) of equipment, instruments and installations.
Dividing skills into five separate groups cannot yet solve the problem of students successfully mastering them. Some children will master organizational skills and abilities well and quickly, others - intellectual, others - technical, etc. Therefore, in accordance with the chemistry program, it is necessary to determine lists of skills that students must master depending on their level of training and individual characteristics. In this regard, all experimental skills can be divided into three levels.
TO first level
These include the typical skills and abilities necessary for all students to master the content of the chemistry curriculum. At this level, students perform practical exercises or laboratory experiments according to instructions and still need supervision and assistance from the teacher. As they master the required skills, it is necessary to require students to demonstrate increasing independence when performing experiments.
Second level
involves the acquisition by students of such skills and abilities that would allow them to perform a chemical experiment without detailed instructions, under changed conditions, to use algorithmic instructions for experiments, and to demonstrate independence in their work. At the same time, such students occasionally need the supervision and help of a teacher.
Third level
constitute skills and abilities characteristic of students who show a deep interest in chemistry, independence and a creative approach when performing a chemical experiment. These students do not need the teacher’s control and assistance.
Below is an approximate list of experimental skills for each level by group.
Organizational skills
First level:
1) drawing up an experimental plan according to the instructions;
2) determination of the list of reagents and equipment according to the instructions;
3) preparation of a report form according to instructions;
4) performing the experiment at a given time, using familiar means, methods and techniques in work;
5) carrying out self-control according to instructions;
6) knowledge of the requirements for written documentation of experimental results;
7) the lack, as a rule, of cleanliness and order in the workplace;
8) the need for systematic control and assistance in work from the teacher.
Second level:
1) drawing up an experimental plan without detailed instructions;
2) determination of the list of reagents and equipment without detailed instructions;
3) preparing a report form without detailed instructions;
4) rational use of time, means, methods and techniques in the course of performing work;
5) carrying out self-control without instructions;
6) written documentation of the results of the experiment using reference literature, with a drawing or diagram;
7) keeping the workplace clean and tidy;
8) occasional need for control and assistance in work from the teacher.
Third level:
1) independent planning of the experiment and its theoretical justification;
2) independent determination of the list of reagents and equipment;
3) making changes to the report form;
4) economical use of time and selection of the most effective means, methods and techniques in the process of performing work;
5) increasing the number of self-control criteria;
6) written documentation of the experiment results using reference and scientific literature, drawings;
7) keeping the workplace clean and tidy throughout the experiment;
8) independent execution of the experiment.
Technical skills
Second level:1) proper handling of various reagents and equipment;
2) assembly of devices and installations from finished parts according to a drawing or diagram without detailed instructions;
3) establishing the order of operations without detailed instructions;
4) constant compliance with all labor safety rules.
Third level:
1) correct handling of various reagents and equipment and replacement of one with another;
2) assembly of devices and installations from finished parts according to the drawing;
3) independently drawing up the order of all operations and performing them during the experiment;
4) strict compliance with all labor safety rules.
Measuring skills
First level:
1) work with measuring instruments in accordance with the instructions;
2) knowledge and use of measurement methods according to instructions;
3) processing of measurement results according to instructions.
Second level:
1) working with measuring instruments without detailed instructions;
2) knowledge and use of measurement methods without detailed instructions;
3) processing of measurement results without detailed instructions.
Third level:
1) independent work with various measuring instruments;
2) use of various measurement methods;
3) involvement of computer equipment, tables, reference literature, etc. in the processing of measurement results.
Intellectual skills
First level:
1) clarifying the purpose and defining the objectives of the experiment according to the instructions;
2) putting forward an experiment hypothesis with the help of a teacher;
3) selection and use of theoretical knowledge as directed by the teacher;
4) observation and identification of characteristic signs of phenomena and processes according to instructions;
5) comparison, analysis, establishment of cause-and-effect relationships, generalization of the results obtained and formulation of conclusions under the guidance of a teacher.
Second level:
1) defining the purpose and objectives of the experiment without detailed instructions;
2) putting forward a hypothesis and determining the content of the experiment with minor assistance from the teacher;
3) use of theoretical knowledge by analogy;
4) observation and establishment of characteristic signs of phenomena and processes without detailed instructions;
5) comparison, analysis, establishment of cause-and-effect relationships, generalization of the results obtained and formulation of conclusions with minor participation of the teacher.
Third level:
1) independent determination of the purpose and objectives of the experiment;
2) independently putting forward a hypothesis and drawing up an algorithm for conducting an experiment;
3) independent use of theoretical knowledge in new conditions;
4) independent observation and identification of characteristic signs of phenomena and processes;
5) independent implementation of synthesis, analysis, establishment of cause-and-effect relationships, generalizations, formulation and comparison of conclusions with the purpose and objectives of the experiment.
Design skills
First level:1) correcting simple problems in equipment, devices and installations according to instructions under the supervision of a teacher;
2) use of ready-made equipment, instruments and installations;
3) production of simple equipment, instruments and installations under the guidance of a teacher;
4) image of equipment, instruments and installations in the form of a drawing.
Second level:
1) repair of equipment, instruments and installations as directed by the teacher;
2) making some changes to the design of equipment, instruments and installations;
3) production of simple equipment, instruments and installations according to instructions;
4) image of equipment, instruments and installations in the form of a diagram.
Third level:
1) independent repair of equipment, devices and installations;
2) improvement of the design of equipment, instruments and installations;
3) production of devices according to drawings;
4) image of equipment, instruments and installations in the form of a drawing.
Students’ work performance at the first level can be assessed with a mark of “3”, at the second – with a mark of “4” and at the third level – with a mark of “5”.
Let's consider the formation of experimental skills using the proposed levels of mastery when performed by 8th grade students practical lesson “Production and properties of oxygen”.
The first group of students completes a not very difficult task (first level).
Option 1
Work tasks:
1) obtain oxygen by decomposing potassium permanganate when heated and collect it by displacing air;
2) prove that the resulting gas is oxygen;
3) check the combustion of coal in oxygen.
Work plan:
1) assemble a device for producing oxygen;
2) check it for leaks (how?);
3) insert a ball of cotton wool into the device (for what?);
4) prepare test tubes, jars or flasks to fill them with oxygen;
5) carefully heat the entire length of the test tube (why?) containing potassium permanganate, and then heat the place where the reagent is located;
6) monitor the beginning of oxygen release (by what sign?);
7) collect the released gas;
8) test the resulting gas in a test tube (how?);
9) study the combustion of coal in air and oxygen;
10) pour a little lime or barite water into the jar or flask in which the coal was burned (what is observed?);
11) draw up an equation for the chemical reaction of coal combustion and draw the appropriate conclusions;
12) draw up a report on the work done.
Questions for self-control.
1) How to check the tightness of a device for producing gases?
2) What role does cotton wool play in a device for producing oxygen from potassium permanganate?
3) How to determine the beginning of oxygen release?
4) How can you recognize oxygen among other gases?
5) How can we explain the unequal combustion of substances in air and oxygen?
The content of the task for this group of students is similar to the instructions given in the textbook. At the same time, it differs from it in that it contains questions that require students not to perform, but to create creative activities. Students complete such tasks in the first lesson, after which they are ready for more complex independent work.
The second group of students completes a more complex task (second level).
Option 2
Job task: consider ways to collect oxygen depending on its solubility and density.
Work plan:
1) obtain oxygen and collect it by displacing water and air;
2) find out the differences in devices for collecting oxygen above water and displacing air;
3) draw up a report on the work done.
Questions for self-control.
1) In what cases can both methods of collecting gases be used with equal success?
2) How does the solubility of gases affect the choice of method for collecting them?
3) How does the density of gases affect the choice of method for collecting them?
4) Is it possible to determine the method of collecting gases by the shape of the gas outlet tube?
Students in the second group are required to justify the feasibility and necessity of their actions before they begin the experiment. Its description is given in general form, and they must not only be able to conduct an experiment, but also draw independent conclusions from the results obtained. This task requires students to be independent in their work and elements of creative activity.
The third group of students is offered the most difficult task (third level).
Option 3
Work tasks:
1) check the possibility of obtaining oxygen from the following substances: KNO 3, H 2 O 2, KMnO 4;
2) find out the conditions for the decomposition reaction for each of these substances;
3) establish which of these substances is most suitable for producing oxygen in the laboratory.
Work plan:
1) list the substances from which oxygen can be obtained in the laboratory;
2) name (or assume) optimal conditions for obtaining oxygen from the substances listed above;
3) develop a plan and independently conduct an experiment to test theoretical assumptions;
4) draw up a report on the work done.
Questions for self-control.
1) What substances can be used to produce oxygen in the laboratory and in practice?
2) What factors influence the choice of substances to produce oxygen in the laboratory and in practice?
Completing this task requires students not only to be able to theoretically substantiate phenomena and generalize the results obtained, but also to obtain the necessary information from scientific and popular science literature. This task is creative in nature.
§ 4.2. The role of observation in the formation process
experimental skills
Observation promotes direct sensory perception of the substances and phenomena being studied. The information obtained in the process of contemplation arouses cognitive interest and contributes to the formation of independence in the knowledge of the surrounding reality. Observation develops observation, logical thinking, and speech. However, observation gives only an external idea of substances and phenomena and does not reveal their inner essence. Attention is concentrated primarily on individual substances and phenomena, and the cause-and-effect relationships between them are not sufficiently disclosed, which limits one’s horizons.
Closely related to observation is experiment, which makes up for this deficiency. With its help, students find out not only the external features of substances and phenomena, but also the internal structure of substances, reveal the essence and patterns of chemical phenomena.
Consequently, if on the basis of observations mainly substantive concepts are formed, then on the basis of experiment - chemical concepts.
The ability to observe ongoing phenomena and processes should be taught continuously. At the same time, it is necessary to ensure that students pay attention not only to external changes, but also at the same time comprehend the inner essence of the occurring phenomena.
By observing, under the guidance of a teacher, the conditions of experiments, signs of reactions and the resulting products and analyzing the results obtained, students enrich their understanding of chemical transformations and processes, and by explaining the reasons that caused them, they learn to apply the acquired theoretical knowledge in practice.
To successfully teach chemistry, a teacher must master a school chemical experiment, as a result of which students acquire the necessary knowledge and skills. A school chemical experiment can be divided into a demonstration experiment, when the experiment is shown by the teacher, and a student experiment, performed by students. In turn, student experiment is divided into two types:
- laboratory experiments conducted by students in the process of acquiring new knowledge;
- practical work that students do after completing one or two topics
In many cases, practical work is carried out in the form of experimental problem solving, in high school - in the form of a workshop, when, after completing a number of topics, practical work is carried out in several lessons.
The development of students' cognitive interests during the learning process is of great importance for any academic subject. The study of chemistry has its own characteristics that are important for teachers to keep in mind. First of all, this concerns the use of educational chemical experiments, which are widely used in schools in various forms. The experiment requires a lot of time from the teacher to prepare and conduct. Only in this case can the expected pedagogical effect be achieved. In this case, it is necessary to take into account both your work experience and the experience of other teachers, known from literature and personal communication. If a teacher is fluent in a chemical experiment and uses it to help students acquire knowledge and skills, then students study chemistry with interest. In the absence of a chemical experiment in chemistry lessons, students' knowledge may acquire a formal connotation - interest in the subject drops sharply.
A chemistry teacher needs to master not only the technique and methodology of demonstration experiments, but also student experiments. Sometimes the simplest experiments may fail when the required concentration of reactants in solutions is not observed or the conditions for conducting chemical reactions are not taken into account. That is why it is necessary to study simple test tube experiments in detail in order to guide the conduct of student experiments in the classroom and provide assistance to students.
Recently, more and more often, student experiments are carried out either by working with a small amount of reagents in small flasks and test tubes, or by the semi-micro method, when experiments are carried out in cells for droplet analysis, solutions are taken with a pipette in a few drops. If you take a paper clip and lower its end into a cell with a solution of copper chloride (11), then after a few seconds the paper clip will be covered with a bright coating of copper. The semi-micromethod saves not only the time of the teacher and students, but also material assets - expensive reagents, materials, and utensils.
Demonstration experiments are the most common type of school chemical experiment, which has a strong influence on the process of students acquiring knowledge in chemistry. When demonstrating experiments, students are especially affected by the following three aspects of the experiment:
1. Direct impact of the chemical reaction itself.
If we arrange in order of importance the factors influencing students during the demonstration of experiments, then first of all they will be influenced by the light stimulus (flashes, combustion, color of the initial and resulting substances). Of great importance are the various odors characteristic of the substances being demonstrated and formed.
during the experiment. They can be pleasant and unpleasant, strong and weak. In cases where substances are poisonous and harmful to health, experiments are carried out under draft or absorption of these substances. The third place will be occupied by auditory stimuli: strong explosions or light sounds that occur during the flash of various substances. Students usually like beeps a lot. Unfortunately, they are not always accompanied by the desired pedagogical effect.
Motor processes (moving liquid and solid substances, rearranging parts when assembling devices) have an important impact on students. For example, students watch with interest the bubbling of gas bubbles in a liquid and the movement of colored solutions. If the processes occurring during a demonstration are little noticeable or poorly perceived by the senses, then the demonstrations are reproduced using various devices. Thus, poorly visible chemical reactions are projected onto a screen using a graphic projector, computer, multimedia, interactive whiteboard, or video. Sometimes it is advisable to combine demonstrations - clearly visible operations are shown in glassware, and individual, poorly visible details are projected onto the screen.
2. The word and actions of the teacher.
It is known that demonstrations are almost never carried out in silence. The teacher guides the students' observation and directs their thoughts depending on the purpose of the demonstration. The nature of this manual most often results in a different pedagogical effect of the demonstration.
The actions of the teacher are also significant: assembling the device, adding solutions, mixing substances, gesturing, etc.
Often these actions have a great influence on students, and they sometimes take them as the main, primary sign, indicating in detail in their notes how the teacher adds solutions and mixes substances.
3. Various visual aids (drawings and diagrams by the teacher, formulas and chemical equations, models, etc.)
All of them help students correctly perceive and comprehend a chemical experiment, emphasize poorly visible details, and contribute to the correct disclosure of the chemistry of the demonstrations.
How do these three aspects of the demonstration experiment affect students? The chemical reactions demonstrated have essential and non-essential features. An essential feature is one without which it is impossible to correctly perceive a chemical process. For example, when demonstrating the interaction of sodium with water, the essential features are the evolution of hydrogen and the formation of alkali. Non-essential features complement the overall picture of the demonstration and make it more complete. In the above example, an insignificant feature is the movement of a piece of sodium along the surface of the water.
When observing essential and non-essential attributes, students are influenced by strong and weak stimuli resulting from a chemical reaction. Sometimes the strong excitement students receive from the action of a powerful stimulus allows them to “shade out” the weak components associated with the essential side of the demonstration of experience. So, in the above example of demonstrating the interaction of an alkali metal with water, students are greatly influenced by a strong stimulus associated with an insignificant feature - the movement of the metal on the surface of the water, and the formation of alkali and hydrogen remains without much attention. When demonstrating an ozonizer, students get the most vivid impression of the noise of the induction coil, which obscures the essence of the chemical process - the formation of ozone. When an explosive mixture (hydrogen and oxygen) explodes in a tin can, the loudest explosion (an insignificant sign) makes the strongest impression on the students, and the main one - the formation of water - passes by the attention of the students, although the teacher informs them about it. It is known that to recognize acids and alkalis, various indicators are used (litmus, phenolphthalein, etc.), which indicate the additional properties of these substances. When demonstrating indicators, as established by D.M. Kiryushin [3], as a result of an incorrect combination of words and actions of the teacher, students indicate a change in the color of acids and alkalis, and not the indicators themselves.
What to do in cases when students, when demonstrating an experiment, mistake unimportant additional features for essential, main ones? Psychologists note that to prevent students from misperceptions or change them, it is necessary to use various verbal instructions from the teacher. Two main types of instructions must be distinguished. You can indicate to students exactly which features of the subject they should pay attention to (positive instructions), and you can indicate which features they should not pay attention to (negative instructions). When teaching chemistry, when students perceive bright flashes and strong explosions as the main sign of a reaction, it is not enough to use only verbal instructions; it is necessary to use various visual aids, for example, color drawings and diagrams in combination with the teacher’s word.
When demonstrating the interaction of alkali metals with water, students’ attention should be drawn to the fact that alkali and hydrogen are formed here. The movement of a piece of metal on the surface of the water should not be ignored. It is advisable for the teacher to ask students the following questions: why is he moving? If hydrogen had not been released, would this phenomenon have been observed? To emphasize the second essential feature of this chemical reaction – the formation of an alkali, students’ attention is drawn to the change in color of the phenolphthalein solution.
An important issue in chemistry demonstration is the number of experiments that the teacher demonstrates in the lesson. V.N. Verkhovsky pointed out the danger of overloading lessons with demonstration chemical experiments. A large number of experiments interferes with the clarity and distinctness of students’ assimilation of the material; unnecessary experiments distract their attention. Even worse results are obtained if the teacher demonstrates an insufficient number of experiences on the basis of which he draws theoretical conclusions. If you show students only the interaction of iron and zinc with acid, then they make a mistake that is difficult to correct even in high school: to produce hydrogen, students offer nitric acid and zinc.
How many experiments should be demonstrated in class? In each individual case, the teacher needs to think about this issue, guided by the fact that their number should be optimal. Students need to be shown all the essential aspects of the demonstrated process with an economical expenditure of time during the lesson, so that as a result they receive conscious and lasting knowledge, not forgetting that a chemical experiment has a great influence on consciousness, sometimes stronger than the teacher’s word.
The cognitive interest of students arises in the process of a fascinating story from the teacher, for example, about a situation in which he once found himself. The story evokes positive emotions in the children, without which, according to psychologists, fruitful learning is impossible. It should be borne in mind that it is always necessary to tell the truth (even if it is unpleasant for the teacher himself), since students do not tolerate falsehood. The life interpretation of the chemical experiment turns out to be the most convincing. Especially in cases where the experiment is unsafe.
While studying white phosphorus, I recalled an incident from my student life when, in a chemical laboratory, a student sitting next to me took a piece of white phosphorus with her hand, which instantly flared up. The student was confused and rubbed the burning phosphorus with her palm over her robe, which also flared up. The fire was extinguished, but the phosphorus severely burned the skin of the hand and, having penetrated the body, caused its poisoning.
While preparing a mixture of berthollet salt with red phosphorus for a demonstration at a chemistry evening, I pressed hard on a lump of berthollet salt, an outbreak occurred - eyebrows, eyelashes, part of the hair were singed, the burning phosphorus got on my hands and caused burns that did not heal for a long time.
A laboratory assistant at the Department of Inorganic Chemistry threw the remaining reagents, including potassium metal, into the sink - an explosion occurred and the ceramic sink shattered into pieces.
A colleague from a neighboring school told me that when she conducted an experiment on the interaction of sodium with water not in a glass, not in a crystallizer, but in a test tube - it burst in her hands from an explosion of detonating gas.
Since the reception of the teacher’s personal experience is limited, the historical experience of chemist scientists should be used more widely, not only based on their achievements, but also without remaining silent about mistakes. Thanks to this, students will understand that the development of chemical science does not follow a smooth, well-trodden path. Usually this is a difficult path of struggle between opinions and evidence.
So, a demonstration experiment in chemistry must be carried out in such a way that it has an emotional impact on the student and contributes to the development of their interest in studying chemistry.
As A. Einstein stated: “A beautiful experiment in itself is often much more valuable than twenty formulas obtained in the retort of abstract thought.”
Literature
- Polosin V.S., Prokopenko V.G. Workshop on methods of teaching chemistry - M.: Education, 1989.
- Polosin V.S. School experiment in inorganic chemistry - M.: Education, 1970.
- Kiryushkin D.M. Experience in researching the interaction of words and visuals in teaching - M.: Publishing house APN, 1980.
- Khomchenko G.P., Platonov F.P., Chertkov I.N. Demonstration experiment in chemistry - M.: Education, 1978.
- Verkhovsky V.N., Smirnov A.D. Technique of chemical experiment at school - M.: Education, 1975.
- Moshchansky V.N. On the pedagogical ideas of Albert Einstein (on the 100th anniversary of his birth) - Soviet Pedagogy, 1979, No. 10
