Solutions play a key role in nature, science and technology. Water is the basis of life, always contains dissolved substances. Fresh water of rivers and lakes contains few dissolved substances, while sea water contains about 3.5% of dissolved salts.
The primordial ocean (during the birth of life on Earth) is thought to have contained only 1% dissolved salts.
“It was in this environment that living organisms first developed, from this solution they scooped up the ions and molecules that are necessary for their further growth and development ... Over time, living organisms developed and transformed, so they were able to leave the aquatic environment and move to land and then rise to air. They obtained these abilities by preserving in their organisms an aqueous solution in the form of liquids that contain a vital supply of ions and molecules, ”the famous American chemist, Nobel Prize winner Linus Pauling describes the role of solutions in nature in these words. Inside each of us, in every cell of our body, there are memories of the primordial ocean, the place where life originated, an aqueous solution that provides life itself.
In any living organism, an unusual solution constantly flows through the vessels - arteries, veins and capillaries, which forms the basis of blood, the mass fraction of salts in it is the same as in the primary ocean - 0.9%. Complex physicochemical processes occurring in the human and animal body also interact in solutions. The process of assimilation of food is associated with the transfer of highly nutritious substances into solution. Natural aqueous solutions are directly related to the processes of soil formation, the supply of plants with nutrients. Such technological processes in the chemical and many other industries, such as the production of fertilizers, metals, acids, paper, occur in solutions. Modern science deals with the study of the properties of solutions. Let's find out what is a solution?
Solutions differ from other mixtures in that the particles of the constituents are evenly distributed in them, and in any microvolume of such a mixture the composition will be the same.
That is why solutions were understood as homogeneous mixtures, which consist of two or more homogeneous parts. This idea was based on the physical theory of solutions.
Adherents of the physical theory of solutions, which van't Hoff, Arrhenius and Ostwald were engaged in, believed that the dissolution process is the result of diffusion.
D. I. Mendeleev and supporters of the chemical theory believed that dissolution is the result of the chemical interaction of a solute with water molecules. Thus, it will be more accurate to define a solution as a homogeneous system that consists of particles of a solute, a solvent, and also the products of their interaction.
Due to the chemical interaction of a solute with water, compounds are formed - hydrates. Chemical interaction is usually accompanied by thermal phenomena. For example, the dissolution of sulfuric acid in water takes place with the release of such an enormous amount of heat that the solution can boil, which is why acid is poured into water, and not vice versa. The dissolution of substances such as sodium chloride, ammonium nitrate, accompanied by the absorption of heat.
M. V. Lomonosov proved that solutions turn into ice at a lower temperature than the solvent.
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MOU Maninskaya secondary school
Open lesson in geography
V class
Teacher:
2008.
Lesson topic: “Water is a solvent. The work of water in nature.
Lesson Objectives:
Introduce students to the importance of water on Earth.
Give the concept of solutions and suspensions, soluble and insoluble substances in water
Show the work of water in nature (creative and destructive)
Cultivate respect for water, love for beauty.
Equipment: map of the hemispheres, globe, statement about water, tables "Sea surf", "Cave", "Ocean", "Inhabitants of the seas and oceans", "Weathering", test tubes with water, salt, sand, filter, tape recorder, TV, multimedia projector .
During the classes.
I.Organizing time.
II.Learning new material.
The lesson starts with watching a movie about water.
Against the background of soft music reflecting the sounds of water.
Teacher:
The boundless expanse of the ocean
And the quiet backwater of the pond,
And it's all just water
The topic of our lesson is “Water is a solvent. The work of water in nature.
The academician clearly and accurately spoke about the role of water in nature. “Is water just a liquid poured into a glass?
The ocean that covers almost the entire planet, our entire wonderful Earth, in which life originated millions of years ago, is water.”
Clouds, clouds, fog, carrying moisture to all living things on the earth's surface - this is also water.
As if dressed in lace
Trees, bushes, wires,
And it seems like a fairy tale
In fact, it's just water.
Boundless variety of life. It is everywhere on our planet. But life is only where there is water. There is no living being if there is no water. Yes, today in our lesson we will talk about water, about the Queen - Voditsa. Let's do a little workout.
Solve riddles.
1. Walks underground
Looks at the sky. ( spring)
2. What is visible when nothing is visible. ( fog)
3. In the evening it flies to the ground,
The night is on earth
In the morning it flies again. ( dew)
4. They fly without wings,
Running without legs
Sailing without a sail. ( clouds)
5. Not a horse, but running,
Not a forest, but noisy. ( river, stream).
6. Came - pounded on the roof,
He left and no one heard him. ( rain)
Let's look at the globe. Our planet is called the Earth by a clear misunderstanding: land accounts for ¼ of its territory, and everything else is water. It would be correct to call it the planet Water! There is a lot of water on earth, but there is no absolutely pure water in nature, it is always present in it, some impurities, some of them are desirable, since they are needed by the human body. Others can be hazardous to health and render the water unusable.
1. Water is a solvent.
There are no substances that, at least to a small extent, do not dissolve in water. Even gold, silver, iron, glass dissolve in water to a small extent. Scientists have calculated that, for example, when we drink a glass of hot tea, we absorb approximately 0.0001 g of dissolved glass with it. Due to the ability of water to dissolve other substances, it can never be called absolutely pure.
Demonstration of experience: water as a solvent.
Pour salt into a glass of water and stir it with a spoon. What happens to salt crystals? They get smaller and smaller and soon disappear altogether. But has the salt disappeared?
No. She dissolved into the water. We got a saline solution.
Pass the salt solution through the filter. Nothing stuck on the filter. The salt solution passed freely through the filter. What is called a solution?
Solution - a liquid containing foreign substances that are evenly distributed in it .
Demonstration of experience: clay experience.
Let's do the same with clay. Clay particles float in water. Let's pass the water through the filter. Water passed through it, and clay particles remained on the filter.
From this experience it can be concluded that clay does not dissolve in water.
How are the results of the two experiments different? ( water with dissolved salt is clear, but water with clay is not)
Indeed, in natural water there may be various particles that do not dissolve in it. Such particles make it cloudy. In this case, one speaks of suspension. After standing for some time, the turbid liquid becomes transparent. Insoluble particles of matter sink to the bottom. And in solutions, no matter how much they stand, substances do not settle to the bottom.
People have long noticed that water poured into silver vessels does not spoil for a long time. The fact is that it contains dissolved silver, which has a detrimental effect on bacteria in the water. "Silver" water is used by astronauts during flights.
How can you prepare silver water at home?
Not only solid and liquid substances dissolve in water, but also gases: oxygen, nitrogen, carbon dioxide.
Oxygen dissolved in water is breathed by fish, plants and animals.
Getting carbonated water is based on the dissolution of carbon dioxide in water.
Physical education "Water is not water"
Mindfulness game. I name the words. If the named word means what contains water (cloud), then the children should stand up. If an object or phenomenon is indirectly related to water (a ship), the children raise their hand. If an object or phenomenon that has no connection with water (wind) is called, the children clap their hands.
Puddle, boat, rain, sand, waterfall, stone, diver, snow, tree, beach, seal, car, cloud.
2. The work of water in nature.
Many phenomena on the surface of the Earth occur with the participation of water.
So, streams of melt water, uniting, become formidable streams, and can bring great destruction. This is how ravines are formed demonstration of "bas-relief", "formation of a ravine").
Water washes away the top layer of fertile soil.
Under the action of water, rocks are slowly destroyed ( story according to the table "Weathering"). In the people there is a proverb "Water wears away a stone."
Seeping into the ground, water erodes and dissolves various rocks. So underground voids are formed - caves ( table "Caves").
Terrible natural disasters such as floods and tsunamis are well known.
During floods and tsunamis, water demolishes bridges, destroys banks and buildings, destroys crops of cultivated plants, and takes human lives.
Student message "Floods".
Flooding is the flooding of the area, settlements, industrial and agricultural facilities, causing damage. Floods lead to the destruction of economic facilities, the death of crops, forests and the forced evacuation of the population from the flood zone. Floods that lead not only to destruction, but also to human casualties, are called catastrophic.
Their cause may be heavy rains, friendly melting of snow after a snowy winter.
Student message "Tsunami"
Tsunamis are a rare but very dangerous natural phenomenon. The word "tsunami" in Japanese means "big wave flooding the bay". These waves can be small and even imperceptible, but they can also be catastrophic. Destructive tsunamis are mainly caused by strong underwater earthquakes at great depths of the seas and oceans, as well as underwater volcanic eruptions. At the same time, billions of tons of water are set in motion in short periods of time. There are low waves running along the surface of the ocean at the speed of a jet aircraft - 700-800 kilometers per hour.
In the open ocean, even the most formidable tsunamis are not at all dangerous. Tragedies are played out when tsunami waves approach the shallow coastal area. On the shore, the waves reach 10-15 meters and higher.
The consequences of a tsunami can be catastrophic: they cause enormous destruction, take hundreds of thousands of human lives.
The largest number of tsunamis originate on the Pacific coast (about once a year).
Teacher: What is the work done by the water in all these examples?
(destructive)
But water does not only destructive work. River water during the spring flood causes fertile silt to separate plots of land. Vegetation develops very well on them.
Not a single process in living organisms takes place without the participation of water. Plants need it to absorb substances from the soil, move them along the stem, leaves, in the form of solutions, for seed germination.
All living and non-living: any soil, rocks, all objects, bodies, organisms - consist of water.
For example, in the human body, water accounts for 60-80% of the total mass.
Water plays an important role in the life of human society. Man has turned reservoirs into transport routes, river flows - a source of cheap electricity.
Water is the habitat of many living organisms that cannot be found on land (f fragment of the video of the film "Inhabitants of the seas and oceans")
Water resources are the national wealth of our country, which requires careful treatment: strict accounting, protection from pollution, and economical use.
Teacher: A Do we always use water sparingly?
Man remember forever:
The symbol of life on earth is water!
Save it and take care -
We are not alone on the planet!
III. Anchoring
1. Questions:
a) What are the names of all the seas and oceans combined ( world Ocean)
b) Not the sea, not the land - the ships do not sail and you can’t walk ( swamp)
b) Drinking water all around is a disaster ( sea)
d) Guess what substance we are talking about: This substance is very common in nature, but practically does not occur in its pure form. Without this substance, life is impossible. Among the ancient peoples, it was considered a symbol of immortality and fertility. In general, this is the most unusual liquid in the world. What is this? ( water).
2. The game "Cross out the excess" (cards with the task on the students' tables)
Task: cross out the extra word and explain why?
a) Snow, ice, steam, hail.
b) Rain, snowflake, sea, river.
c) Hail, water vapor, snow, rain.
3. And now the next task. Fill in the gaps in the text:
Water ... solvent. It dissolves solids.
For example... : liquid substances, for example... gaseous substances,
For example…
In this regard, it is impossible to find ... water in nature.
4. The game "Extra Property"
Task: Cross out the property that does not apply to water.
Property:
a) Has a color, has no color.
b) Has a taste, has no taste.
c) Odorless, odorless.
d) Opaque, transparent.
e) Has fluidity, does not have fluidity.
e) Heats up quickly and cools down quickly, heats up slowly and cools down slowly.
g) Dissolves sand and chalk, dissolves salt and sugar.
h) Has a form, does not have a form.
Against the background of music
Teacher:
Water is a wonderful natural gift,
Alive flowing and free,
Paints pictures of our life.
In its three important hypostases.
Now a stream, then a river winds,
It pours from the glass to the ground.
It freezes like a thin piece of ice
Beautifully named snowflake.
That takes on the lightness of steam:
She was there and suddenly she was gone.
Great worker Voditsa,
Well, how can she not admire.
She floats towards us in clouds,
Drinking snow and rain
And destroys and inflicts
And so it asks for our care.
IV. Homework§ 23, task 77 workbook. page 45
Water is one of the most common compounds on earth. It is not only in rivers and seas; All living organisms also contain water. Life is impossible without it. Water is a good solvent (different substances dissolve easily in it). Animals and plant sap are composed primarily of water. Water exists forever; it is constantly moving from the soil to the atmosphere and organisms and vice versa. More than 70% of the earth's surface is covered with water.
What is water
The water cycle
The water of rivers, seas, lakes constantly evaporates, turning into tiny drops of water vapor. The drops gather together to form, from which the water falls to the ground in the form of rain. This is the water cycle in nature. In the clouds, the vapor cools and returns to earth in the form of rain, snow or hail. Wastewater from sewers and factories is treated and then dumped into the sea.
Water station
River water necessarily contains impurities, so it must be purified. Water enters the reservoirs, where it settles and solid particles settle to the bottom. The water then passes through filters that trap any remaining solids. Water percolates through layers of clean gravel, sand or activated carbon, where it is cleaned of dirt and solid impurities. After filtration, the water is treated with chlorine to kill pathogenic bacteria, after which it is pumped into tanks and fed to residential buildings and factories. Before sewage goes into the sea, it must be treated. At the water treatment plant, it is passed through filters that trap dirt, then pumped to septic tanks, where solid particles must settle to the bottom. Bacteria destroy the remains of organic substances, decomposing them into harmless components.
Water purification
Water is a good solvent, so it usually contains impurities. You can purify water with distillation(see article ""), but a more effective cleaning method is deionization(desalting). Ions are atoms or molecules that have lost or gained electrons and, as a result, have received a positive or negative charge. For deionization, a substance called ion exchanger. It has positively charged hydrogen ions (H +) and negatively charged hydroxide ions (OH -) When contaminated water passes through the ion exchanger, the impurity ions are replaced by hydrogen and hydroxide ions from the ion exchanger. Hydrogen and hydroxide ions combine to form new water molecules. Water that has passed through the ion exchanger no longer contains impurities.
Water as a solvent
Water is an excellent solvent, many substances dissolve easily in it (see also the article ""). That is why pure water is rarely found in nature. In a water molecule, the electric charges are slightly separated, since the hydrogen atoms are located on one side of the molecule. Because of this, ionic compounds (compounds made up of ions) dissolve so easily in it. Ions are charged and water molecules attract them.
Water, like all solvents, can only dissolve a limited amount of a substance. A solution is called saturated when the solvent cannot dissolve an additional portion of the substance. Typically, the amount of a substance that a solvent can dissolve increases with heat. Sugar dissolves more easily in hot coda than in cold coda. Effervescent drinks are aqueous carbon dioxide diffusers. The higher , the more gas the solution can absorb. Therefore, when we open a can of a drink and thereby reduce the pressure, carbon dioxide escapes from the drink. When heated, the solubility of gases decreases. In 1 liter of river and sea water, about 0.04 grams of oxygen is usually dissolved. This is enough for algae, fish and other inhabitants of the seas and rivers.
hard water
Minerals are dissolved in hard water, which got there from the rocks through which the water flowed. 
In such water, soap does not lather well, because it reacts with minerals and forms flakes. There are two types of hard water; the difference between them is in the type of dissolved minerals. The type of minerals dissolved in water depends on the type of rocks through which the water flows (see figure). Temporary hardness of water occurs when limestone reacts with rainwater. Limestone is an insoluble calcium carbonate and rainwater is a weak solution of carbonic acid. The acid reacts with calcium carbonate to form bicarbonate, which dissolves in water and hardens it.
When water boils or evaporates with temporary hardness, some of the minerals precipitate, forming scale at the bottom of the kettle or stalactites and stalagmites in the cave. Water with constant hardness contains other calcium and magnesium compounds, such as gypsum. These minerals do not precipitate when boiled.
Water softening
You can remove the minerals that make water hard by adding washing soda to the solution or by ion exchange, a process similar to the deionization of water during purification. A substance containing sodium ions that are exchanged with calcium and magnesium ions in water. In an ion exchanger, hard water passes through zeolite- a substance containing sodium. In zeolite, calcium and magnesium ions are mixed with sodium ions, which do not give water hardness. Washing soda is sodium carbonate. In hard water, it reacts with calcium and magnesium compounds. The result is insoluble compounds that do not form flakes.
Water pollution
When untreated water from factories and homes enters the seas and rivers, water pollution occurs. If there is too much waste in the water, organic-decomposing bacteria multiply and consume almost all of the oxygen. In such water, only pathogenic bacteria that can live in water without oxygen survive. When the level of dissolved oxygen in the water decreases, fish and plants die. Garbage, pesticides and nitrates from fertilizers also get into the water, poisonous ones - lead, mercury. Poisonous substances, including metals, enter the body of fish, and from them - into the bodies of other animals and even humans. Pesticides kill microorganisms and animals, thereby disturbing the natural balance. Fertilizers from the fields and detergents containing phosphates, getting into the water, cause increased plant growth. Plants and bacteria that feed on dead plants take up oxygen, reducing its content in the water.
Brief description of the role of water for organisms
Water is the most important inorganic compound, without which life is impossible on. This substance is also the most important part, and plays a large role as an external factor for all living beings.
On planet Earth, water is found in three states of aggregation: gaseous (vapors in, liquid (water in and foggy in the atmosphere) and solid (water in glaciers, icebergs, etc.). The formula of vaporous water is H 2 O, liquid (H 2 O) 2 (at T \u003d 277 K) and (H 2 O) n - for solid water (ice crystals), where n \u003d 3, 4, ... (depends on temperature - the lower the temperature, the greater the value of n). Water molecules combine into particles with the formula (H 2 O) n as a result of the formation of special chemical bonds called hydrogen; such particles are called associates; due to the formation of associates, looser structures arise than liquid water, therefore, at a temperature below 277 K, the density of water, unlike other substances, it does not increase, but decreases, as a result, ice floats on the surface of liquid water and deep reservoirs do not freeze to the bottom, especially since water has low thermal conductivity.This is of great importance for organisms living in water - they do not die in severe frosts and survive during the winter cold until more favorable temperature conditions.
The presence of hydrogen bonds determines the high heat capacity of water, which makes life possible on the surface of the Earth, since the presence of water helps to reduce the temperature difference day and night, as well as in winter and summer, because when cooled, water condenses and heat is released, and when heated, water evaporates, on the breaking of hydrogen bonds is spent and the Earth's surface does not overheat.
Water molecules form hydrogen bonds not only among themselves, but also with molecules of other substances (carbohydrates, proteins, nucleic acids), which is one of the reasons for the emergence of a complex of chemical compounds, as a result of which the existence of a special substance is possible - a living substance that forms various .
The ecological role of water is enormous and has two aspects: it is both an external (first aspect) and an internal (second aspect) environmental factor. As an external environmental factor, water is part of abiotic factors (humidity, habitat, an integral part of climate and microclimate). As an internal factor, water plays an important role inside the cell and inside the body. Consider the role of water inside the cell.
In the cell, water performs the following functions:
1) the environment in which all the organelles of the cell are located;
2) a solvent for both inorganic and organic substances;
3) environment for the occurrence of various biochemical processes;
4) a catalyst for exchange reactions between inorganic substances;
5) reagent for the processes of hydrolysis, hydration, photolysis, etc.;
6) creates a certain state of the cell, such as turgor, which makes the cell elastic and mechanically strong;
7) performs a building function, consisting in the fact that water is part of various cellular structures, such as membranes, etc.;
8) is one of the factors that unite all cellular structures into a single whole;
9) creates an electrical conductivity of the medium, converting inorganic and organic compounds into a dissolved state, causing electrolytic dissociation of ionic and highly polar compounds.
The role of water in the body is that it:
1) performs a transport function, since it converts substances into a soluble state, and the resulting solutions due to various forces (for example, osmotic pressure, etc.) move from one organ to another;
2) performs a conductive function due to the fact that the body contains electrolyte solutions capable of conducting electrochemical impulses;
3) binds together individual organs and organ systems due to the presence of special substances (hormones) in water, while carrying out humoral regulation;
4) is one of the substances that regulate the body temperature of the body (water in the form of sweat is released to the surface of the body, evaporates, due to which heat is absorbed and the body cools down);
5) is included in food products, etc.
The significance of water outside the body is described above (habitat, environmental temperature regulator, etc.).
For organisms, fresh water plays an important role (salt content less than 0.3%). In nature, chemically pure water practically does not exist, the most pure is rainwater from rural areas, remote from large settlements. Water contained in fresh water bodies - rivers, ponds, fresh lakes - is suitable for organisms.
Water is the most important chemical compound on earth. Water is the main component of all living organisms and the environment in which a person lives and exists. The physical properties of water differ sharply from the properties of other substances, and the nature of these differences determines the nature of the physical and biological world.
Over time, living organisms evolved, which allowed them to leave the aquatic environment and move to land and rise into the air. They acquired this ability by retaining in their organisms an aqueous solution in the form of a liquid component of tissue, blood plasma and intercellular fluids containing the necessary supply of ions and molecules.
Water, unlike organic solvents, dissolves salts well, since it has a very high permittivity (about 81 at room temperature) and its molecules tend to combine with ions to form hydrated ions . Both of these properties are due to the large electric dipole moment of 1 water molecule. And this property of water plays an important role in the development of life and metabolism.
The following process takes place in water. The force of attraction or repulsion of electric charges is inversely proportional to the permittivity of the medium surrounding these charges. This means that two opposite electric charges are mutually attracted in water with a force equal to 1/80 of the force of their mutual attraction in air (or in vacuum). Therefore, if a sodium chloride salt crystal is in water, then the ions that form it are separated from the crystal much more easily than if the crystal were in air, since the electrostatic force that attracts the ion back to the surface of the crystal from an aqueous solution is only 1/80 of the force attraction of a given ion from the air. Therefore, it is not surprising that at room temperature thermal motion cannot cause the transition of ions from the crystal into air, but at the same time, the thermal motion of ions is quite sufficient to overcome the relatively weak attraction when the crystal is surrounded by water, which leads to the transition of a large number ions into an aqueous solution.
Ion hydration
When salts dissolve in water, they form hydrated ions . The formation of hydrated ions leads to the stabilization of ions in water solutions. Each negative ion attracts the positive ends of several nearby water molecules and tends to keep them around.
Positive ions, which are usually smaller than anions, attract water even more strongly; each cation attracts the negative ends of water molecules and firmly binds several molecules, holding them near itself; in this case, a hydrate is formed, which can be quite stable, especially in the case of cations bearing a double or triple positive charge.
The number of water molecules attached to a given cation, its ligand, determined by the size of the cation. The ligandity of an atom is equal to the number of atoms associated with it or in contact with it. Ligandity is also called coordination number .
In water, a small Be 2 + cation forms Be(OH 2) 4 2+ tetrahydrate. Somewhat large ions, for example Mg 2+ or Al 3+, form hexahydrates Mg (OH 2) 6 2+, Al (OH 2) 6 3+ ( picture 1).
Figure 1. Structure of hydrated ions Be ( Oh 2 ) 4 2+ And A l (HE 2 ) 6 3+ .
In hydrated ions, the interaction forces between cations and water molecules are so strong that ions often retain a layer of water molecules around them, even in crystals. Such water is called crystallization But th. This effect is more pronounced in the case of doubly and triply charged cations than in the case of singly charged ones. For example, the tetrahydrate complex Be(OH 2) 4 2+ is found in various salts, including BeCO 3 . 4Н 2 О, ВеС1 2 . 4H 2 O and BeSO 4 . 4H 2 O and is undoubtedly present in solution.
MgCl 2 6 H 2 OA1C1 3 6H 2 ABOUT
Mg(C1ABOUT 3 ) 2 6H 2 OKA1(S0 4 ) 2 12H 2 O
Mg(C1ABOUT 4 ) 2 6 H 2 0 Fe(NH 4 ) 2 (SO 4 ) 2 6H 2 O
MgSiF 6 6H 2 OFe(NO 3 ) 2 6H 2 O
NiSnCl 3 6H 2 OFeCl 3 6H 2 O
In a crystal such as FeSO 4 . 7H 2 O, six water molecules are attached to the iron ion in the form of the Fe(OH 2) 6 2+ complex, and the seventh occupies a different position in the crystal, located near the sulfate ion.
In alum KAl(SO 4) 2 . 12H 2 O, six of the twelve water molecules are bound to the aluminum ion, and the remaining six are located around the potassium ion.
There are also crystals in which the cations are devoid of some or all of the water molecules. Thus, magnesium sulfate forms three crystalline compounds: MgSO 4 . 7H 2 O, MgSO 4 . H 2 O and MgSO 4.
The stability of ions in an aqueous solution is the result of such a distribution of electric charge between a certain number of atoms, in which not a single atom shows a significant deviation from electrical neutrality. Consider the hydrated cations Be(OH 2) 4 2+ and A1(OH 2) 6 3+ shown in Figure 1. Both beryllium and aluminum have an electronegativity of 1.5, while the electronegativity of oxygen is 3.5. The difference in electronegativity corresponds to an ionicity slightly above 50%, sufficient to transfer half of the electrical charge of each bond to the central atom, leaving it roughly neutral. O-H bonds can be 25% ionic, with the entire charge of the ions transferred to eight hydrogen atoms in Be(OH 2) 4 2+ and to twelve hydrogen atoms in A1(OH 2) 6 3+, each of which will have a charge of ¼ + In addition, each of these hydrogen atoms can participate in the formation of a weak bond with another water molecule in such a way that its charge will be neutralized by interaction with the electron pair of the oxygen atom, and then the total charge of the hydrated cations Be (OH 2) 4 (OH 2) 8 2+ and Al(OH 2) 6 (OH 2) 12 3+ will be distributed between the most distant hydrogen atoms, each of which will have a charge of 1/8 +. In fact, this electric polarization of water propagates over long distances; this is what determines the high dielectric constant of water.
It is known that when hydrogen bonds are formed in aqueous solutions by molecules such as H 3 RO 4 , all four oxygen atoms can become almost equivalent, providing almost complete resonance of the double bond between four positions. At such a resonance, each oxygen atom has a valence of 1 1/4, satisfying the bonds of phosphorus and leaving 3/4 for bonding with hydrogen. If each of the three OH groups uses its hydrogen atom to form a weak bond (in ¼ bond) with the oxygen atom of the water molecule, then the remaining ¾ bonds will be sufficient to make the oxygen atoms of the phosphate electrically neutral. Similarly, phosphate oxygen without a hydrogen atom can form weak (¼) bonds with the hydrogen atoms of three neighboring water molecules, which makes it also electrically neutral.
Each of the four oxygen atoms of the vital phosphate ion PO 4 3 can similarly form hydrogen bonds with three water molecules. The electrical charge of the hydrated PO 4 (HOH) 12 3 ion will then be distributed among the twelve outer oxygen atoms, each with a ¼- charge. Analogous hydrated structures are formed by (HO) 2 PO 2 - and HOPO 3 2- ions, which are present in almost equal amounts in living organisms.
Clathrate compounds
Noble gases (argon, etc.), simple hydrocarbons, and many other substances form the so-called crystalline hydrates with water; thus, xenon forms Xe hydrate. 5 3 /4 H 2 O, stable at about 2°C and a xenon partial pressure of 1 atm; methane forms a similar CH 4 hydrate. 5 3 /4 H 2 O.
X-ray studies have shown that these crystals have a structure in which water molecules form a lattice resembling an ice lattice due to hydrogen bonds; in it, each water molecule is surrounded by four other molecules located at the vertices of a tetrahedron at a distance of 276 pm, but with a more open arrangement of molecules, which causes the formation of cavities (in the form of pentagonal dodecahedrons or other polyhedra with pentagonal or hexagonal faces) large enough to gas atoms or other molecules could be placed in them ( figure 2). Crystals of this type are called clathrate crystals .
The structure of xenon hydrate and hydrates of argon, krypton, methane, chlorine, bromine, hydrogen sulfide and some other substances is shown in fig. 2. The cubic cell of this structure has an edge of about 1200 pm and contains 46 water molecules.
Figure 2. Structure of a clathrate crystal of xenon hydrate.
Xenon atoms occupy voids (eight per cubic cell) in a three-dimensional lattice, formingbath water molecules with the participation of hydrogen bonds (46 molecules per cubic cell). Rasthe O-H O position is 276 pm, as in an ice crystal. Two xenon atoms at the oxygen atoms О О О and ½ ½ ½ are located in the centers of almost regular pentagonal dodecahedrons. The remaining six xenon atoms atAbout ¼ ½;O ¾ ½; ½ O¼; 1/2O ¾; ¼ ½ Oare located in the centers of fourteen-hedrons. EveryThis fourteen hexahedron (one of them is highlighted in the center of the figure) has 24 vertices (moleculeswater), two hexagonal faces and 12 pentagonal faces.
Hydrate of chloroform CHC1 3 . 17H 2 O has a somewhat more complex structure, in which the chloroform molecule is surrounded by a 16 sided polyhedron formed by 28 water molecules. Clathrate compounds can also be obtained, in which the crystal lattice with hydrogen bonds is formed by organic molecules, for example, urea (H 2 N) 2 CO molecules.
An interesting interpretation of the mechanism of action of chemically inert anesthetics, such as halothane F 3 CCBrClH and xenon, has been proposed. According to this mechanism, the anesthetic substance disrupts the aqueous structure of the intercellular or intracellular fluid by forming clathrate structures that affect the normal intercellular communication systems. Local anesthetics differ in their mechanism of action. Their molecules can form hydrogen bonds, and probably the anesthetic effect is the result of the combination of anesthetic molecules with protein molecules or other molecules that make up the nerves.
Other electrolyte solvents
In addition to water, some other liquids can serve as ionizing solvents for electrolytes with the formation of solutions that conduct electric current. These fluids include hydrogen peroxide, hydrogen fluoride, liquid ammonia, and hydrogen cyanide. Like water, all these liquids have a high dielectric constant. Low dielectric liquids such as benzene or carbon disulfide are not ionizing solvents.
Liquids with a high dielectric constant are sometimes referred to as polar liquids .
The high dielectric constant of water, which accounts for the amazing ability of water to dissolve ionic substances, is partly due to the fact that water is able to form hydrogen bonds. Thanks to these bonds, the water molecules are arranged so as to partially neutralize the electric field. Hydrogen bonds are also formed in other liquids - in hydrogen peroxide, hydrogen fluoride, ammonia (boiling point - 33.4 ° C), hydrogen cyanide], which are capable of dissolving substances with an ionic structure.
Solubility
An isolated system is in equilibrium , when its properties, in particular the distribution of components between phases, remain constant for a long time.
If a system in equilibrium consists of a solution and another phase, which is one of the components of the solution in the form of a pure substance, then the concentration of this substance in the solution is called solubility of this substance. The solution in this case is called rich .
For example, a solution of borax at 0°C containing 1.3 g of anhydrous sodium tetraborate Na 2 B 4 O 7 in 100 g of water is in equilibrium with the solid phase of Na 2 B 4 O 7 . 10H 2 O (sodium tetraborate decahydrate); over time, this system does not change, the composition of the solution remains constant. Solubility Na 2 B 4 O 7 . 10H 2 O in water is therefore 1.3 g Na 2 B 4 O 7 per 100 g, or, taking into account the water of hydration, 2.5 g Na 2 B 4 O 7 . 10H 2 O per 100 g of water.
Change in the solid phase
Solubility Na 2 B 4 O 7 . 10H 2 O increases rapidly with increasing temperature; at 60 ° C, the solubility already reaches 20.3 g of Na 2 B 4 O 7 per 100 g. ( figure 3). When the system is heated to 70 °C and kept for some time at this temperature, a new phenomenon is observed - a third phase appears - crystalline, having the composition Na 2 B 4 O 7 . 5H 2 O, and the former crystalline phase disappears. At this temperature, the solubility of the decahydrate is higher than the solubility of the pentahydrate; a solution saturated with decahydrate turns out to be supersaturated with respect to pentahydrate, and therefore crystals of pentahydrate precipitate from such a solution. To induce the crystallization process, sometimes it is necessary to add a “seed” to the solution (small crystals of a substance that is dissolved in this solution). Subsequently, the process of dissolution of the unstable phase and crystallization of the stable phase proceeds until the unstable phase disappears. The third sodium tetraborate hydrate is Na 2 B 4 O 7 kernite. 4H 2 O - has a greater solubility than the other two.
Figure 3 Solubility Na 2 SO 4 . 10 H 2 O
In the case considered, the decahydrate is less soluble than the pentahydrate at temperatures up to 61°C, and is therefore a stable phase below this temperature. The solubility curves of these two hydrates intersect at 61°C, and above this temperature the pentahydrate is stable in contact with the solution.
In a stable solid phase, in addition to solvation, other processes can occur. Thus, rhombic sulfur is less soluble in certain solvents than monoclinic sulfur at temperatures below 95.5 °C, i.e., below the temperature of the mutual transformation of these two forms; above this temperature, the monoclinic form is less soluble. The principles of thermodynamics require that the temperature at which the solubility curves of two forms of a substance intersect be the same for all solvents and at the same time be the temperature at which the vapor pressure curves intersect.
Temperature dependence of solubility
The solubility of a substance may increase or decrease with increasing temperature. In this regard, sodium sulfate is a convincing example. Solubility Na 2 SO 4 . 10H 2 O (stable solid below 32.4°C) increases very rapidly with increasing temperature, increasing from 5 g Na 2 SO 4 per 100 g water at 0°C to 55 g at 32.4°C. Above 32.4 ° C, the stable solid phase is Na 2 SO 4; the solubility of this phase decreases rapidly with increasing temperature: from 55 g at 32.4°C to 42 g at 100°C ( figure 4).
Figure 4 Solubility Na 2 SO 4 . 10 H 2 O temperature dependent
The solubility of most salts increases with increasing temperature; the solubility of many salts (NaCl, K 2 CrO 7) only slightly changes with increasing temperature; and only some salts, for example, Na 2 SO 4 , FeSO 4 . H 2 O and Na 2 CO 3. H 2 O, have a solubility that decreases with increasing temperature ( figure 4 And figure 5).
Figure 5. Solubility curves for some salts in water
Dependence of solubility on the nature of the solute and solvent
The solubility of substances varies greatly in different solvents. Nevertheless, several general rules regarding solubility have been established, which apply mainly to organic compounds.
One of these rules states that a substance tends to dissolve in solvents that are chemically similar to it. Thus, the hydrocarbon naphthalene C 10 H 8 has a high solubility in gasoline, which is a mixture of hydrocarbons, somewhat less solubility in ethyl alcohol C 2 H 5 OH, the molecules of which consist of short hydrocarbon chains with hydroxyl groups, and very poor solubility in water, which is very different from hydrocarbons. At the same time, boric acid B (OH) 3, which is a hydroxide, has moderate solubility in water and alcohol, i.e., in substances that contain hydroxyl groups, and is insoluble in gasoline. The three solvents mentioned themselves confirm the same rule: both gasoline and water are miscible with alcohol (dissolve in it), while gasoline and water are mutually soluble only in very small quantities.
These facts can be explained as follows: hydrocarbon groups (consisting only of carbon and hydrogen atoms) attract each other very weakly, as evidenced by the lower melting and boiling points of hydrocarbons compared to other substances of approximately the same molecular weight. At the same time, there is a very strong intermolecular attraction between hydroxyl groups and water molecules; the melting and boiling points of water lie above the corresponding temperatures of any other substance with a small molecular weight. This strong attraction is due, in part, to the ionic nature of the O-H bonds, due to which an electric charge is imposed on the atoms. The positively charged hydrogen atoms are then attracted to the negatively charged oxygen atoms of other molecules, forming hydrogen bonds and holding the molecules firmly together.
Term hydrophilic often used in relation to substances or groups that attract water, and the term hydrophobic applied to substances or groups that repel water and attract hydrocarbons. In fact, the molecules of a hydrophobic substance act by the forces of electronic van der Waals attraction on both water molecules and hydrocarbon molecules. The solubility of water vapor, for example, in kerosene (a mixture of hydrocarbons) at 25 ° C and a pressure of 0.0313 atm (i.e., at a saturated vapor pressure over liquid water at this temperature) is 72 mg per 1 kg of solvent, while as the solubility of methane at the same partial pressure is somewhat less - 10 mg in 1 kg of kerosene. Water molecules are attracted by kerosene molecules somewhat stronger than methane molecules. The difference between water and methane is that at higher partial pressures, water vapor condenses into a liquid, which is stabilized by intermolecular hydrogen bonds, while methane continues to be a gas.
The solubility of methane in polar solvents is almost the same as in non-polar ones; in alcohols from methanol CH 3 OH to pentanol (amyl alcohol) C 5 H 11 OH, the solubility of methane is 72-80% of the value for kerosene. The forces of van der Waals attraction of solvent molecules with respect to methane molecules remain almost the same for different solvents. On the other hand, the solubility of water vapor at a pressure of 0.313 atm in amyl alcohol is 1400 times greater than in kerosene, and water is miscible in any ratio with light alcohols.
Substances consisting of small non-polar molecules, such as oxygen, nitrogen and methane, dissolve in water about 10 times worse than in non-polar solvents. Substances composed of larger non-polar molecules are essentially insoluble in water, but tend to be highly soluble in non-polar solvents. Water, as it were, counteracts the inclusion of these molecules, since the formation of voids necessary for this is associated with a break or deformation of hydrogen bonds between water molecules. Compounds like gasoline and naphthalene do not dissolve in water because their molecules in solution would prevent water molecules from forming as many strong hydrogen bonds as they do in pure water; on the other hand, boric acid is soluble in water because the decrease in the number of bonds between water molecules is compensated by the formation of strong hydrogen bonds between water molecules and hydroxyl groups of boric acid molecules.
Solubility of salts and hydroxides in water
When studying inorganic chemistry, especially qualitative analysis, it is useful to know the approximate solubility of widely used substances. Simple solubility rules are given below. These rules apply to compounds of ordinary cations: Na +, K +, NH 4 +, Mg 2+, Ca 2+, Sr 2 +, Ba 2 +, Al 3+, Cr 3+ , Mn 2+, Fe 2+, Fe 3+, Co 2+, Ni 2+, Cu 2+, Zn 2+, Ag+, Cd 2+, Sn 2+, Hg 2 2+, Hg 2+ and Pb 2+ . When a substance is said to be "soluble", it means that its solubility exceeds about 1 g per 100 ml (about 0.1 M by cation), and when they say that a substance is “insoluble”, this means that its solubility does not exceed 0.1 g in 100 ml (approximately 0.01 M): Substances with solubility within or close to these limits are called moderate solutionrime.
Soluble class:
All nitrates soluble.
All acetates soluble.
All chlorides , bromides And iodides soluble, with the exception of the corresponding compounds of silver, mercury (I) (mercury with an oxidation state of + 1) and lead. The PbCl 2 and PbBr 2 compounds are moderately soluble in cold water (1 g in 100 ml at 20°C) and better soluble in hot water (3 and 5 g in 100 ml at 100°C, respectively).
All sulfates soluble, with the exception of barium, strontium and lead sulfates. Moderately soluble CaSO 4 , Ag 2 SO 4 and Hg 2 SO 4 .
All salts on three I, potassium And ammonium soluble: the exception is NaSb (OH) 6 (sodium antimonate), K 2 PtCl 6 (potassium hexachloroplatinate), (NH 4) 2 PtCl 6, K 3 Co (TO 2) 6 (potassium hexanitrocobaltate), (NH 4) sCo ( NO 2) 6 and KclO 4 .
Class of insoluble substances :
All hydroxides insoluble, with the exception of hydroxides of alkali metals, ammonium and barium; Ca(OH) 2 and Sr(OH) 2 are sparingly soluble.
All medium carbonates And phosphates insoluble, except for the corresponding compounds of alkali metals and ammonium. Many acid carbonates and phosphates, such as Ca (HCO 3) 2 and Ca (H 2 PO 4) 2, are soluble.
All sulfides , with the exception of alkali metal sulfides, ammonium and alkaline earth metals, insoluble.
K. x. n. O. V. Mosin
Literary source : L. Pauling, P. Pauling. / translated by M. V. Sakharov. Ed. M. L. Karapetyants. Chemistry., Moscow 1978
Margarita Khalisova
Summary of the lesson “Water is a solvent. Water Purification»
Subject: Water is a solvent. Water purification.
Target: consolidate the understanding that substances in water do not disappear, but dissolve.
Tasks:
1. Identify substances that dissolve in the water and which are not dissolve in water.
2. Familiarize yourself with the cleaning method water - filtering.
3. Create conditions for identifying and testing various cleaning methods water.
4. Consolidate knowledge about the rules of safe behavior when working with various substances.
5. Develop logical thinking by modeling problem situations and solving them.
6. To cultivate accuracy and safe behavior when working with various substances.
7. Raise interest in cognitive activity, experimentation.
Educational areas:
cognitive development
Socio-communicative development
Physical development
vocabulary work:
enrichment: filter, filtering
activation: funnel
preliminary work: talks about water, its role in human life; conducted observations of water in kindergarten, at home; experiments with water; looked at illustrations on the topic « Water» ; got acquainted with safety rules during research and experimentation; guessing riddles about water; reading fiction, ecological fairy tales; water games.
Demonstration-visual material: doll in blue suit "Droplet".
Handout: empty glasses, with water; solvents: sugar, salt, flour, sand, food coloring, vegetable oil; plastic spoons, funnels, gauze napkins, cotton pads, oilcloth aprons, tea mugs, lemon, jam, disposable plates, oilcloth on tables.
GCD progress
caregiver: - Guys, before starting a conversation with you, I want to make a wish for you riddle:
Lives in seas and rivers
But often it flies through the sky.
And how bored she is to fly
Falls to the ground again. (water)
Guess what the conversation will be about? That's right, water. We already know that water is a liquid.
Let's take a look at the properties water we have established with the help of experiments on others classes. List.
Children:
1. Do no smell of water.
2. No taste.
3. She is transparent.
4. Colorless.
5. Water takes the shape of the vessel into which it is poured.
6. Has weight.
caregiver: - Right. Do you want to experiment with water again? To do this, we need to briefly turn into scientists and look into our laboratory experimentation:
Turn right, turn left
Be in the laboratory.
(children approach the mini-laboratory).
caregiver: - Guys, look who is visiting us again? And what's new in the lab?
Children: - "Droplet", grandfather's granddaughter Knowing and beautiful box.
Want to know what's in this box? Guess puzzles:
1. Separately - I'm not so tasty,
But in food - everyone needs (salt)
2. I am white as snow,
In honor of everyone.
Got in the mouth -
There he disappeared. (sugar)
3. Cheesecakes are baked from me,
And pancakes and pancakes.
If you are making dough
I must be put (flour)
4. Yellow, not the sun,
It pours, not water,
Foaming in the pan
Splashes and hisses (oil)
Food coloring - used in cooking to decorate cakes, paint eggs.
Sand - for construction, play with it in the sandbox.
Children examine test tubes with substances.
caregiver: - All these substances brought "Droplet" in order for us to help her figure out what will happen to water when interacting with them.
caregiver: - What do we need in order to start our work with water?
Children: - Aprons.
(children put on oilcloth aprons and go to the table, where there are glasses of clean water on a tray).
caregiver: - Let's remember the rules before we start working with these substances:
Children:
1. You can not taste substances - there is a possibility of poisoning.
2. Care must be taken when sniffing, as substances can be very caustic and can burn the respiratory tract.
caregiver: - Danil will show you how to do it right (directing the smell from the glass with the palm of your hand).
I. Research Job:
caregiver: - Guys, what do you think will change if dissolve these substances in water?
I listen to the expected result of the children before mixing the substances with water.
caregiver: - Let's check.
I suggest that the children each take a glass of water.
caregiver: - Look and determine which one is there water?
Children: - The water is clear, colorless, odorless, cold.
caregiver: - Take a test tube with the substance you have chosen and dissolve in a glass of water stirring with a spoon.
We are considering. I listen to the answers of the children. Did they guess correctly?
caregiver: - What happened to sugar, salt?
salt and sugar quickly dissolve in water, water stays clear, colorless.
Flour too dissolve in water, But the water becomes cloudy.
But after the water stays a little, the flour settles to the bottom, but solution continues to be cloudy.
Water with sand it became dirty, cloudy, if you don’t interfere anymore, then the sand sank to the bottom of the glass, you can see it, that is, it doesn’t dissolved.
food powder solvent quickly changed color water, Means, dissolves well.
Oil not dissolves in water: it either spreads on its surface with a thin film, or floats in water in the form of yellow droplets.
Water is a solvent! But not all substances dissolve in it.
caregiver: - Guys, we worked with you and "Droplet" invites us to rest.
(Children sit at another table and a game is played.
A game: "Guess the drink taste (tea)».
Tea drinking with different flavors: sugar, jam, lemon.
II Experimental work.
Let's go to table 1.
caregiver: - Guys, is it possible to purify water from these substances that we dissolved? Return it to its previous state of transparency, without sediment. How to do it?
I suggest you take your glasses with solutions and go to table 2.
caregiver: - You can filter it. This requires a filter. What can a filter be made of? We will make it with a gauze pad and a cotton pad. I show (I put a gauze napkin folded in several layers into the funnel, a cotton pad and put it in an empty glass).
We make filters with children.
I show the filtration method, and then the children themselves filter the water with the substance they have chosen.
I remind you that the children are not in a hurry, poured in a small stream solution into a funnel with a filter. I'm talking proverb: "Hurry up - make people laugh".
Consider what happened after filtering water with different substances.
The oil was filtered out quickly because it does not dissolved in water, traces of oil are clearly visible on the filter. The same thing happened with the sand. Substances that are well dissolved in water: sugar, salt.
Water with flour after filtering became more transparent. Most of the flour settled on the filter, only very small particles slipped through the filter and ended up in a glass, so water not entirely transparent.
After filtering the dye, the color of the filter has changed, but the filtered solution also remained in color.
Outcome of GCD:
1. What substances dissolve in water? - sugar, salt, dye, flour.
2. What substances are not dissolve in water - sand, oil.
3. What kind of cleaning method water we met? - filtering.
4. With what? - filter.
5. Did everyone follow the safety rules? (one example).
6. What is interesting (new) did you find out today?
caregiver: - You learned today that water is a solvent, checked which substances dissolve in water and how to purify water from various substances.
"Droplet" thanks you for your help and gives you an album for sketching experiments. This concludes our research, we return from the laboratory to group:
Turn right, turn left.
Find yourself in the group again.
Literature:
1. A. I. Ivanova Ecological observations and experiments in kindergarten
2. G. P. Tugusheva, A. E. Chistyakova Experimental activity of children of middle and senior preschool age St. Petersburg: Detstvo-Press 2010.
3. Cognitive research activities of older preschoolers - A child in kindergarten No. 3,4,5 2003.
4. Research activity of a preschooler - D / in No. 7 2001.
5. Experimenting with water and air - D / V No. 6 2008.
6. Experimental activities in kindergarten - Educator of preschool educational institution No. 9 2009.
7. Games - experimentation of a younger preschooler - Preschool pedagogy No. 5 2010.
