Class: 10
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1. The purpose of the lesson: to acquaint students with the general and specific properties of methane acid in the course of completing the tasks of the crossword puzzle "Chemistry of formic acid", including when solving problems to derive the formula of organic matter (see. Annex 1 ) (slides 1-2).
2. Type of lesson: lesson learning new material.
3. Equipment: computer, projector, screen, videos of a chemical experiment (oxidation of formic acid with potassium permanganate and decomposition of formic acid under the action of concentrated sulfuric acid), presentation for the lesson, worksheets for students (see. Annex 2 ).
4. Lesson progress
When studying the structure of formic acid, the teacher reports that this acid is different from the rest of the members of the homologous series of saturated monocarboxylic acids, because. the carboxyl group is linked not to the hydrocarbon radical –R, but to the H-atom ( slide 3). Students come to the conclusion that formic acid exhibits the properties of both carboxylic acids and aldehydes, i.e. is aldehyde acid (slide 4).
The study of the nomenclature is carried out in the process of solving the problem ( slide 5): « Salts of a limiting monobasic carboxylic acid are called formates. Name this acid (according to the IUPAC nomenclature) if it is known that it contains 69.5% oxygen". The solution of the problem is drawn up by one of the students of the class on the blackboard. The answer is ant or methane acid ( slide 6).
Next, the teacher informs the students slide 7) that formic acid is found in the acrid secretions of stinging caterpillars and bees, in stinging nettles, needles, some fruits, in the sweat and urine of animals, and in acidic secretions ants, where it was discovered in 1794 by the German chemist Marggraf Andreas-Sigismund ( slide 8).
When studying the physical properties of formic acid, the teacher reports that it is a colorless, caustic liquid with a pungent odor and a burning taste, having boiling and melting points close in values to water (tboil = 100.7 o C, tpl. = 8.4 o C ). Like water, it forms hydrogen bonds, therefore, in the liquid and solid states, it forms linear and cyclic associates ( slide 9), is miscible with water in any ratio (“like dissolves like”). Next, one of the students is asked to solve the problem at the blackboard: It is known that the nitrogen vapor density of formic acid is 3.29. Therefore, it can be argued that in the gaseous state, formic acid exists in the form ...» In the course of solving the problem, students come to the conclusion that in the gaseous state, formic acid exists in the form dimers– cyclic associates ( slide 10).
Obtaining formic acid ( slide 11-12) we study on the following examples:
1. Oxidation of methane on a catalyst:
2. Hydrolysis of hydrocyanic acid (here students should be reminded that a carbon atom cannot have more than two hydroxyl groups at the same time - dehydration occurs with the formation of a carboxyl group):
3. Interaction of potassium hydride with carbon monoxide (IV):
4. Thermal decomposition of oxalic acid in the presence of glycerol:
5. Interaction of carbon monoxide with alkali:
6. The most profitable way (from the point of view of economic costs - a waste-free process) for obtaining formic acid is to obtain an ester of formic acid (with subsequent acid hydrolysis) from carbon monoxide and saturated monohydric alcohol:
Since the last method of obtaining formic acid is the most promising, students are further invited to solve the following problem at the blackboard ( slide 12): “Set the formula of alcohol, which is repeatedly (returning to the cycle) used for reaction with carbon monoxide (II), if it is known that the combustion of 30 g of ether produces 22.4 liters of carbon dioxide and 18 g of water. Set the name of this alcohol. In the course of solving the problem, students come to the conclusion that for the synthesis of formic acid, methyl alcohol ( slide 13).
When studying the action of formic acid on the human body ( slide 14) the teacher informs the students that formic acid vapors irritate the upper respiratory tract and mucous membranes of the eyes, exhibit an irritating effect or corrosive effect - cause chemical burns (slide 15). Next, schoolchildren are invited to find in the media or in reference publications ways to eliminate the burning sensation caused by the action of nettles and ant stings (the test is carried out in the next lesson).
We begin to study the chemical properties of formic acid ( slide 16) from reactions with breaking the O-H bond (substitution of the H-atom):
To consolidate the material, it is proposed to solve the following problem ( slide 18): « When 4.6 g of formic acid interacted with an unknown saturated monohydric alcohol, 5.92 g of an ester was formed (it is used as a solvent and an additive to some varieties of rum to give it a characteristic aroma, it is used in the production of vitamins B1, A, E). Set the formula of the ether if it is known that the reaction yield is 80%. Name the ester according to the IUPAC nomenclature. In the course of solving the problem, tenth-graders come to the conclusion that the resulting ester is - ethyl formate (slide 19).
The teacher reports slide 20) that reactions with C-H bond cleavage (at the α-C-atom) for formic acid not typical, because R=H. And the reaction with breaking the C-C bond (decarboxylation of salts of carboxylic acids leads to the formation of alkanes!) leads to the production of hydrogen:
As examples of acid reduction reactions, we present the interaction with hydrogen and a strong reducing agent, hydroiodic acid:
Acquaintance with oxidation reactions proceeding according to the scheme ( slide 21):
expedient to carry out during the task ( slide 22):
« Match the formulas of the reagents, the reaction conditions with the reaction products"(the teacher can show the first equation as an example, and offer the rest to students as homework):
| UNSD + | Reagent, reaction conditions | Product 1 |
Product 2 |
|||
| 1) | Ag 2 O, NH 3 , t o C | 1) | CO | 1) | – | |
| 2) | Br 2 (solution) | 2) | CO, H2O | 2) | K2SO4, MnSO4 | |
| 3) | KMnO4, H 2 SO 4 , t o C | 3) | H2O | 3) | Cu 2 Ov | |
| 4) | Сl 2 (solution) | 4) | CO2 | 4) | HCl | |
| 5) | Cu(OH) 2 (fresh), t o C | 5) | CO2, H2O | 5) | Agv | |
| 6) | Ir or Rh | 6) | CO2, H2 | 6) | HBr | |
| 7) | H2O2 | 7) | CO, H2 | 7) | H-C(O)OOH | |
Answers should be written as a sequence of numbers.
Answers:
| 1) 2) 3) 4) 5) 6) 7) |
5 4 5 4 5 6 3 |
5 6 2 4 3 1 7 |
When compiling equations, students come to the conclusion that in all these reactions, oxidation formic acid, because it is a strong reducing agent ( slide 23).
The study of the issue "The use of formic acid" is carried out upon acquaintance with the scheme ( slide 24).
Students clarify the use of “ant alcohol” in medicine (you can go online) and call the disease - rheumatism(slide 25).
If there is free time, the teacher informs the students ( slide 26) that earlier "ant alcohol" was prepared by insisting ants on alcohol.
Reports that the total world production of formic acid has been on the rise in recent years as in all countries of the world, the death of bees from mites (Varroa) is observed: gnawing through the chitinous cover of bees, they suck out the hemolymph, and the bees die (formic acid is an effective remedy against these mites).
5. Lesson summary
At the end of the lesson, students summarize: evaluate the work of classmates at the blackboard, explain what new educational material (general and specific properties of formic acid) they met.
6. Literature
1. Deryabina N.E. Organic chemistry. Book 1. Hydrocarbons and their monofunctional derivatives. Textbook-notebook. - M .: IPO "At the Nikitsky Gates", 2012. - S. 154-165.
2. Kazennova N.B. Schoolchildren's Handbook of Organic Chemistry/For secondary school. - M.: Aquarium, 1997. - S. 155-156.
3. Levitina T.P. Handbook of Organic Chemistry: Textbook. - St. Petersburg: "Parity", 2002. - S. 283-284.
4. Tutor in chemistry / Ed. A.S. Egorova. 14th ed. - Rostov n / D: Phoenix, 2005. - S. 633-635.
5. Rutzitis G.E., Feldman F.G. Chemistry 10. Organic Chemistry: Textbook for 10 cells. secondary school. - M., 1992. - S. 110.
6. Chernobelskaya G.M. Chemistry: textbook. allowance for medical educate. Institutions/ G.M. Chernobelskaya, I.N. Chertkov.- M.: Bustard, 2005. - S.561-562.
7. Atkins P. Molecules: Per. from English. - M.: Mir, 1991. - S. 61-62.
Interaction of formic acid with ammonia solutionsilver hydroxide(reaction of a silver mirror). The formic acid molecule HCOOH has an aldehyde group, so it can be opened in solution by reactions characteristic of aldehydes, for example, by the silver mirror reaction.
An ammonia solution of argentum (Ι) hydroxide is prepared in a test tube. To do this, 1 - 2 drops of a 10% solution of sodium hydroxide are added to 1 - 2 ml of a 1% solution of argentum (Ι) nitrate, the resulting precipitate of argentum (Ι) oxide is dissolved by adding dropwise a 5% solution of ammonia. 0.5 ml of formic acid is added to the resulting clear solution. The test tube with the reaction mixture is heated for several minutes in a water bath (water temperature in the bath is 60 0 -70 0 C). Metallic silver is released as a mirror coating on the walls of the test tube or as a dark precipitate.
HCOOH + 2Ag [(NH 3) 2 ]OH → CO 2 + H 2 O + 2Ag + 4NH 3
b) Oxidation of formic acid with potassium permanganate. Approximately 0.5 g of formic acid or its salt, 0.5 ml of a 10% solution of sulfate acid and 1 ml of a 5% solution of potassium permanganate are placed in a test tube. The tube is closed with a stopper with a gas outlet tube, the end of which is lowered into another tube with 2 ml of lime (or barite) water, and the reaction mixture is heated.
5HCOOH + 2KMnO 4 + 3H 2 SO 4 → 5CO 2 + 8H 2 O + K 2 SO 4 + 2MnSO 4
V) Decomposition of formic acid when heated withconcentrated sulfuric acid. (Thrust!) Add 1 ml of formic acid or 1 g of its salt and 1 ml of concentrated sulfate acid into a dry test tube. The tube is closed with a stopper with a gas outlet tube and gently heated. Formic acid decomposes to form carbon(II) oxide and water. Carbon (II) oxide is ignited at the opening of the gas outlet tube. Pay attention to the nature of the flame.
After completion of work, the test tube with the reaction mixture must be cooled to stop the release of toxic carbon monoxide.
Experience 12. Interaction of stearic and oleic acids with alkali.
Dissolve approximately 0.5 g of stearin in diethyl ether (without heating) in a dry test tube and add 2 drops of a 1% alcohol solution of phenolphthalein. Then, a 10% solution of sodium hydroxide is added dropwise. The crimson color that appears at the beginning disappears when shaken.
Write the equation for the reaction of stearic acid with sodium hydroxide. (Stearin is a mixture of stearic and palmitic acids.)
C 17 H 35 COOH + NaOH → C 17 H 35 COONa + H 2 O
sodium stearate
Repeat the experiment using 0.5 ml of oleic acid.
C 17 H 33 COOH + NaOH → C 17 H 33 COONa + H 2 O
sodium oleate
Experience13. The ratio of oleic acid to bromine water and potassium permanganate solution.
A) Reaction of oleic acid with bromine water Pour 2 ml of water into a test tube and add about 0.5 g of oleic acid. The mixture is shaken vigorously.
b) Oxidation of oleic acid with potassium permanganate. 1 ml of a 5% potassium permanganate solution, 1 ml of a 10% sodium carbonate solution and 0.5 ml of oleic acid are placed in a test tube. The mixture is vigorously stirred. Note the changes that occur with the reaction mixture.
Experience 14. Sublimation of benzoic acid.
The sublimation of small amounts of benzoic acid is carried out in a porcelain cup, closed with the wide end of a conical funnel (see Fig. 1), the diameter of which is somewhat smaller than the diameter of the cup.
The nose of the funnel is fixed in the leg of the tripod and tightly covered with cotton wool, and in order to prevent sublimation from falling back into the cup, it is covered with a round piece of filter paper with several holes in it. A porcelain cup with small crystals of benzoic acid (t pl \u003d 122.4 0 C; sublimates below t pl) is carefully slowly heated on a small flame of a gas burner (on an asbestos grid). You can cool the top funnel by applying a piece of filter paper soaked in cold water. After the sublimation stops (after 15-20 minutes), the sublimate is carefully transferred with a spatula into a flask.
Note. For work, benzoic acid can be contaminated with sand.
The test tube in which the emulsion has formed is closed with a stopper under reflux, heated in a water bath until boiling starts and shaken. Does the solubility of oil increase when heated?
The experiment is repeated, but instead of sunflower oil, a small amount of animal fat (pork, beef or mutton fat) is added to test tubes with organic solvents,
b) Determination of the degree of unsaturation of fat by reaction with brominewater. (Thrust!) 0.5 ml of sunflower oil and 3 ml of bromine water are poured into a test tube. The contents of the tube are shaken vigorously. What happens to bromine water?
V) The interaction of vegetable oil with an aqueous solution of potassiumpermanganate (reaction of E. E. Wagner). About 0.5 ml of sunflower oil, 1 ml of a 10% sodium carbonate solution and 1 ml of a 2% potassium permanganate solution are poured into a test tube. Shake the contents of the tube vigorously. The purple color of potassium permanganate disappears.
Discoloration of bromine water and reaction with an aqueous solution of potassium permanganate are qualitative reactions to the presence of a multiple bond (unsaturation) in an organic molecule.
G) Saponification of fat with an alcohol solution of sodium hydroxide In a conical flask with a capacity of 50 - 100 ml, 1.5 - 2 g of solid fat is placed and 6 ml of a 15% alcoholic solution of sodium hydroxide is poured. The flask is stoppered with an air cooler, the reaction mixture is stirred and the flask is heated in a water bath with shaking for 10–12 min (water temperature in the bath is about 80 0 C). To determine the end of the reaction, a few drops of the hydrolyzate are poured into 2-3 ml of hot distilled water: if the hydrolyzate dissolves completely, without the release of fat drops, then the reaction can be considered complete. After saponification is completed, soap is salted out from the hydrolyzate by adding 6–7 ml of a hot saturated sodium chloride solution. The released soap floats, forming a layer on the surface of the solution. After settling, the mixture is cooled with cold water, the hardened soap is separated.
Chemistry of the process on the example of tristearin:
Experience 17. Comparison of the properties of soap and synthetic detergents
A) relation to phenolphthalein. Pour 2-3 ml of a 1% solution of laundry soap into one test tube, and the same amount of a 1% solution of synthetic washing powder into another. Add 2-3 drops of phenolphthalein solution to both tubes. Can these detergents be used to wash alkali-sensitive fabrics?
b) relation to acids. Add a few drops of a 10% solution of acid (chloride or sulfate) to solutions of soap and washing powder in test tubes. Does foam form when shaken? Do the detergent properties of the studied products remain in an acidic environment?
C 17 H 35 COONa+HCl→C 17 H 35 COOH↓+NaCl
V) AttitudeTocalcium chloride. To solutions of soap and washing powder in test tubes, add 0.5 ml of a 10% solution of calcium chloride. Shake the contents of the tubes. Does this produce foam? Can these detergents be used in hard water?
C 17 H 35 COONa + CaCl 2 → Ca (C 17 H 35 COO) 2 ↓ + 2NaCl
Experience 18 . Interaction of glucose with an ammonia solution of argentum (Ι) oxide (silver mirror reaction).
0.5 ml of a 1% solution of argentum (Ι) nitrate, 1 ml of a 10% solution of sodium hydroxide are poured into a test tube, and a 5% solution of ammonia is added dropwise until the precipitate of argentum (Ι) hydroxide is dissolved. Then add 1 ml of 1% glucose solution and heat the contents of the tube for 5-10 minutes in a water bath at 70 0 - 80 0 C. Metallic silver is released on the walls of the tube in the form of a mirror coating. During heating, the test tubes must not be shaken, otherwise metallic silver will stand out not on the walls of the test tubes, but in the form of a dark precipitate. To obtain a good mirror, a 10% sodium hydroxide solution is first boiled in test tubes, then they are rinsed with distilled water.
Pour 3 ml of 1% sucrose solution into a test tube and add 1 ml of 10% sulfuric acid solution. The resulting solution is boiled for 5 min, then cooled and neutralized with dry sodium bicarbonate, adding it in small portions with stirring (carefully, the liquid foams from the evolved carbon monoxide (IY)). After neutralization (when the evolution of CO 2 stops), an equal volume of Fehling's reagent is added and the upper part of the liquid is heated until boiling begins.
Does the color of the reaction mixture change?
In another test tube, a mixture of 1.5 ml of a 1% sucrose solution with an equal volume of Fehling's reagent is heated. Compare the results of the experiment - the reaction of sucrose with Fehling's reagent before hydrolysis and after hydrolysis.
C 12 H 22 O 11 + H 2 O C 6 H 12 O 6 + C 6 H 12 O 6
glucose fructose
Note. In a school laboratory, Fehling's reagent can be replaced with cuprum (ΙΙ) hydroxide.
Experience 20. Hydrolysis of cellulose.
In a dry conical flask with a capacity of 50 - 100 ml, put some very finely chopped pieces of filter paper (cellulose) and moisten them with concentrated sulfate acid. Thoroughly mix the contents of the flask with a glass rod until the paper is completely destroyed and a colorless viscous solution is formed. After that, 15 - 20 ml of water is added to it in small portions with stirring (carefully!), The flask is connected to an air reflux condenser and the reaction mixture is boiled for 20 - 30 minutes, stirring it periodically. After hydrolysis is completed, 2–3 ml of liquid is poured, neutralized with dry sodium carbonate, adding it in small portions (the liquid foams), and the presence of reducing sugars is detected by reaction with Fehling's reagent or cuprum (ΙΙ) hydroxide.
(C 6 H 10 O 5)n+nH 2 O→nC 6 H 12 O 6
Cellulose glucose
Experience 21. Interaction of glucose with cuprum (ΙΙ) hydroxide.
a) Place 2 ml of 1% glucose solution and 1 ml of 10% sodium hydroxide into a test tube. Add 1-2 drops of a 5% solution of cuprum (ΙΙ) sulfate to the resulting mixture and shake the contents of the test tube. The bluish precipitate of cuprum (II) hydroxide formed at the beginning instantly dissolves, a blue transparent solution of cuprum (ΙΙ) saccharate is obtained. Process chemistry (simplified):- 
b) The contents of the test tube are heated over the flame of the burner, holding the test tube at an angle so that only the upper part of the solution is heated, and the lower part remains unheated (for control). When gently heated to boiling, the heated part of the blue solution turns orange-yellow due to the formation of cuprum (Ι) hydroxide. With longer heating, a precipitate of cuprum (Ι) oxide may form.
Experience 22. Interaction of sucrose with metal hydroxides. A) Reaction with cuprum (ΙΙ) hydroxide) in an alkaline medium. In a test tube, mix 1.5 ml of a 1% sucrose solution and 1.5 ml of a 10% sodium hydroxide solution. Then, a 5% solution of cuprum (ΙΙ) sulfate is added dropwise. The initially formed pale blue precipitate of cuprum (ΙΙ) hydroxide dissolves upon shaking, the solution acquires a blue-violet color due to the formation of complex cuprum (ΙΙ) saccharate.
b) Obtaining calcium sucrose. Into a small glass (25 - 50 ml) pour 5 - 7 ml of a 20% sucrose solution and add freshly prepared milk of lime dropwise with stirring. Calcium hydroxide dissolves in sucrose solution. The ability of sucrose to give soluble calcium sucrose is used in industry to purify sugar when it is isolated from sugar beets. V) Specific color reactions. 2-5 ml of a 10% sucrose solution and 1 ml of a 5% sodium hydroxide solution are poured into two test tubes. Then a few drops are added to one test tube. 5- percentage solution of cobalt (ΙΙ) sulfate, in another - a few drops 5- percentage solution of nickel (ΙΙ) sulfate. In a test tube with a cobalt salt, a violet color appears, and a green color appears with a nickel salt, Experiment 23. Interaction of starch with iodine. 1 ml of a 1% solution of starch paste is poured into a test tube and then a few drops of iodine strongly diluted with water in potassium iodide are added. The contents of the tube turn blue. The resulting dark blue liquid is heated to a boil. The color disappears, but reappears on cooling. Starch is a heterogeneous compound. It is a mixture of two polysaccharides - amylose (20%) and amylopectin (80%). Amylose is soluble in warm water and gives a blue color with iodine. Amylose consists of almost unbranched chains of glucose residues with a screw or helix structure (approximately 6 glucose residues in one screw). A free channel with a diameter of about 5 microns remains inside the helix, into which iodine molecules are introduced, forming colored complexes. When heated, these complexes are destroyed. Amylopectin is insoluble in warm water, swells in it, forming a starch paste. It consists of branched chains of glucose residues. Amylopectin with iodine gives a reddish-violet color due to the adsorption of iodine molecules on the surface of the side chains. Experience 24. hydrolysis of starch. A) Acid hydrolysis of starch. In a conical flask with a capacity of 50 ml, pour 20 - 25 ml of 1% starch paste and 3 - 5 ml of a 10% solution of sulfate acid. In 7 - 8 tubes pour 1 ml of a very dilute solution of iodine in potassium iodide (light yellow), the tubes are placed in a tripod. 1-3 drops of the starch solution prepared for the experiment are added to the first test tube. Note the resulting color. The flask is then heated on an asbestos grid with a small burner flame. 30 seconds after the start of boiling, a second sample of the solution is taken with a pipette, which is added to the second test tube with an iodine solution, after shaking, the color of the solution is noted. In the future, samples of the solution are taken every 30 seconds and added to subsequent test tubes with iodine solution. Note the gradual change in color of the solutions upon reaction with iodine. The color change occurs in the following order, see table.
After the reaction mixture ceases to give color with iodine, the mixture is boiled for another 2-3 minutes, after which it is cooled and neutralized with a 10% sodium hydroxide solution, adding it dropwise until the medium is alkaline (the appearance of a pink color on phenolphthalein indicator paper). Part of the alkaline solution is poured into a test tube, mixed with an equal volume of Fehling's reagent or a freshly prepared suspension of cuprum (ΙΙ) hydroxide, and the upper part of the liquid is heated until boiling begins.
(
Soluble
Dextrins
C 6 H 10 O 5) n (C 6 H 10 O 5) x (C 6 H 10 O 5) y
maltose
n/2 C 12 H 22 O 11 nC 6 H 12 O 6
b) Enzymatic hydrolysis of starch.
A small piece of black bread is chewed well and placed in a test tube. A few drops of a 5% solution of cuprum (ΙΙ) sulfate and 05 - 1 ml of a 10% solution of sodium hydroxide are added to it. The test tube with the contents is heated. 3. Technique and methodology for demonstration experiments on obtaining and studying the properties of nitrogen-containing organic substances.
Equipment: chemical beakers, glass rod, test tubes, Wurtz flask, dropping funnel, chemical glass, glass vapor tubes, connecting rubber tubes, splinter.
Reagents: aniline, methylamine, litmus and phenolphthalein solutions, concentrated chloride acid, sodium hydroxide solution (10%), bleach solution, concentrated sulfate acid, concentrated nitrate acid, egg white, copper sulfate solution, plumbum (ΙΙ) acetate, phenol solution , formalin.
Experience 1. Getting methylamine. Add 5-7 g of methylamine chloride to a Wurtz flask with a volume of 100 - 150 ml and close the stopper with an addition funnel inserted into it. Connect the gas outlet tube with a rubber tube with a glass tip and lower it into a glass of water. Add potassium hydroxide solution (50%) drop by drop from the funnel. Heat the mixture in the flask gently. Salt decomposes and methylamine is released, which is easily recognizable by its characteristic smell, which resembles the smell of ammonia. Methylamine is collected at the bottom of the glass under a layer of water: + Cl - +KOH → H 3 C - NH 2 + KCl + H 2 O
Experience 2. burning of methylamine. Methylamine burns with a colorless flame in air. Bring a burning splinter to the opening of the gas outlet tube of the device described in the previous experiment and observe the combustion of methylamine: 4H 3 C - NH 2 + 9O 2 → 4CO 2 +10 H 2 O + 2N 2
Experience 3. The ratio of methylamine to indicators. Pass the resulting methylamine into a test tube filled with water and one of the indicators. Litmus turns blue, and phenolphthalein becomes crimson: H 3 C - NH 2 + H - OH → OH This indicates the basic properties of methylamine.
Experience 4. Formation of salts by methylamine. a) A glass rod moistened with concentrated hydrochloric acid is brought to the opening of the test tube from which gaseous methylamine is released. The wand is shrouded in mist.
H 3 C - NH 2 + HCl → + Cl -
b) Pour 1-2 ml into two test tubes: into one - a 3% solution of ferum (III) chloride, into the other a 5% solution of cuprum (ΙΙ) sulfate. Gaseous methylamine is passed into each tube. In a test tube with a solution of ferum (III) chloride, a brown precipitate precipitates, and in a test tube with a solution of cuprum (ΙΙ) sulfate, the blue precipitate that forms at first dissolves to form a complex salt, colored bright blue. Process chemistry:
3 + OH - + FeCl 3 → Fe (OH) ↓ + 3 + Cl -
2 + OH - + CuSO 4 →Cu(OH) 2 ↓+ + SO 4 -
4 + OH - + Cu (OH) 2 → (OH) 2 + 4H 2 O
Experience 5. Reaction of aniline with hydrochloric acid. In a test tube with 5 ml of aniline add the same amount of concentrated hydrochloric acid. Cool the tube in cold water. A precipitate of aniline hydrogen chloride precipitates. Pour some water into a test tube with solid hydrogen chloride aniline. After stirring, aniline hydrogen chloride dissolves in water.
C 6 H 5 - NH 2 + HCl → Cl - Experiment 6. Interaction of aniline with bromine water. Add 2-3 drops of aniline to 5 ml of water and shake the mixture vigorously. Add bromine water dropwise to the resulting emulsion. The mixture becomes colorless and a white precipitate of tribromaniline precipitates.
Experience 7. Fabric dyeing with aniline dye. Wool dyeing And silk with acid dyes. Dissolve 0.1 g of methyl orange in 50 ml of water. The solution is poured into 2 glasses. To one of them add 5 ml of a 4N solution of sulfate acid. Then pieces of white woolen (or silk) fabric are lowered into both glasses. Solutions with tissue are boiled for 5 minutes. Then the fabric is taken out, washed with water, squeezed and dried in air, hung on glass rods. Pay attention to the difference in the color intensity of the pieces of fabric. How does the acidity of the environment affect the fabric dyeing process?
Experience 8. Proof of the presence of functional groups in amino acid solutions. a) Detection of the carboxyl group. To 1 ml of a 0.2% solution of sodium hydroxide, colored pink with phenolphthalein, add dropwise a 1% solution of aminoacetate acid (glycine) until the mixture of HOOC - CH 2 - NH 2 + NaOH → NaOOC - CH 2 - NH 2 becomes colorless + H 2 O b) Detection of the amino group. To 1 ml of a 0.2% solution of perchloric acid, colored blue by the Congo indicator (acidic medium), add dropwise a 1% solution of glycine until the color of the mixture changes to pink (neutral medium):
HOOC - CH 2 - NH 2 + HCl → Cl -
Experience 9. Action of amino acids on indicators. Add 0.3 g of glycine to a test tube and add 3 ml of water. Divide the solution into three test tubes. Add 1-2 drops of methyl orange to the first tube, the same amount of phenolphthalein solution to the second, and litmus solution to the third. The color of the indicators does not change, which is explained by the presence of acidic (-COOH) and basic (-NH 2) groups in the glycine molecule, which are mutually neutralized.
Experience 10. Protein precipitation. a) In two test tubes with a protein solution, add dropwise solutions of copper sulfate and plumbum (ΙΙ) acetate. Flocculent precipitates are formed, which dissolve in an excess of salt solutions.
b) Equal volumes of phenol and formalin solutions are added to two test tubes with a protein solution. Observe protein precipitation. c) Heat the protein solution in a burner flame. Observe the turbidity of the solution, which is due to the destruction of the hydration shells near the protein particles and their increase.
Experience 11. Color reactions of proteins. a) Xantoprotein reaction. Add 5-6 drops of concentrated nitrate acid to 1 ml of protein. When heated, the solution and the precipitate turns bright yellow. b) Biuret reaction. To 1 - 2 ml of protein solution add the same amount of diluted copper sulphate solution. The liquid turns red-violet. The biuret reaction makes it possible to identify a peptide bond in a protein molecule. The xantoprotein reaction occurs only if the protein molecules contain residues of aromatic amino acids (phenylalanine, tyrosine, tryptophan).
Experience 12. Reactions with urea. A) Solubility of urea in water. Placed in a test tube 0,5 g of crystalline urea and gradually add water until the urea is completely dissolved. A drop of the resulting solution is applied to red and blue litmus paper. What reaction (acidic, neutral or alkaline) does an aqueous solution of urea have? In aqueous solution, urea is in the form of two tautomeric forms:
b) hydrolysis of urea. Like all acid amides, urea is easily hydrolyzed in both acidic and alkaline media. Pour 1 ml of a 20% urea solution into a test tube and add 2 ml of clear barite water. The solution is boiled until a precipitate of barium carbonate appears in the test tube. Ammonia released from the test tube is detected by the blue color of wet litmus paper.
H 2 N - C - NH 2 + 2H 2 O → 2NH 3 + [HO - C - OH] → CO 2
→H 2 O 
Ba(OH) 2 + CO 2 →BaCO 3 ↓+ H 2 O
c) Biuret formation. Heat in a dry test tube 0,2 g urea. First, urea melts (at 133 C), then, upon further heating, it decomposes with the release of ammonia. Ammonia is detected by smell (carefully!) and by the blue of wet red litmus paper brought to the opening of the test tube. After some time, the melt in the test tube solidifies despite continued heating:
Cool the tube, add 1-2 ml of water and with low heating dissolve the biuret. In addition to biuret, the melt contains a certain amount of cyanuric acid, which is sparingly soluble in water, so the solution is cloudy. When the precipitate settles, pour the biuret solution from it into another test tube, add a few drops of a 10% sodium hydroxide solution (the solution becomes transparent) and 1-2 drops of a 1% solution of cuprum (ΙΙ) sulfate. The solution turns pink-violet. Excess cuprum (ΙΙ) sulfate masks the characteristic color, causing the solution to turn blue, and should therefore be avoided.
Experience 13. Functional analysis of organic substances. 1. Qualitative elemental analysis of organic compounds. The most common elements in organic compounds, in addition to carbon, are hydrogen, oxygen, nitrogen, halogens, sulfur, phosphorus. Conventional qualitative analysis methods are not applicable to the analysis of organic compounds. To detect Carbon, Nitrogen, Sulfur and other elements, organic matter is destroyed by fusion with sodium, while the elements under study are converted into inorganic compounds. For example, Carbon goes into carbon (IV) oxide, Hydrogen - into water, Nitrogen - into sodium cyanide, Sulfur - into sodium sulfide, halogens - into sodium halides. The elements are then discovered by conventional methods of analytical chemistry.
1. Detection of Carbon and Hydrogen by oxidation of substance cuprum(II) oxide.
Device for the simultaneous detection of carbon and hydrogen in organic matter:
1 - dry test tube with a mixture of sucrose and cuprum (II) oxide;
2 - test tube with lime water;
4 - anhydrous cuprum (ΙΙ) sulfate.
The most common, universal method of detection in organic matter. carbon and at the same time hydrogen is the oxidation of cuprum (II) oxide. In this case, carbon is converted into carbon (IU) oxide, and Hydrogen is converted into water. Place 0.2 - 0.3 g of sucrose and 1 - 2 g of cuprum (II) oxide powder. The contents of the test tube are thoroughly mixed, the mixture is covered with a layer of cuprum (II) oxide on top. - about 1 g. A small piece of cotton wool is placed in the upper part of the test tube (under the cork), on which is sprinkled with a little anhydrous copper (II) sulfate. The test tube is closed with a cork with a gas outlet tube and fixed in the leg of the tripod with a slight inclination towards the cork. I lower the free end of the gas outlet tube into a test tube with lime (or barite) water so that the tube almost touches the surface of the liquid. First, the entire test tube is heated, then the part where the reaction mixture is located is strongly heated. Note what happens to the lime water. Why does the color of cuprum (ΙΙ) sulfate change?
Chemistry of processes: C 12 H 22 O 11 + 24CuO → 12CO 2 + 11H 2 O + 24Cu
Ca (OH) 2 + CO 2 → CaCO 3 ↓ + H 2 O
CuSO 4 +5H 2 O → CuSO 4 ∙ 5H 2 O
2. Beilstein test on on halogens. When organic matter is calcined with cuprum (II) oxide, it is oxidized. Carbon turns into carbon (ІУ) oxide, Hydrogen - into water, and halogens (except fluorine) form volatile halides with Cuprum, which color the flame bright green. The response is very sensitive. However, it should be borne in mind that some other cuprum salts, such as cyanides, formed during the calcination of nitrogen-containing organic compounds (urea, pyridine derivatives, quinoline, etc.), also color the flame. The copper wire is held by the plug and its other end (loop) is calcined in the flame of the burner until the coloring of the flame stops and a black coating of cuprum(II) oxide forms on the surface. The cooled loop is moistened with chloroform, poured into a test tube, and again introduced into the flame of the burner. First, the flame becomes luminous (Carbon burns), then an intense green color appears. 2Cu+O 2 →2CuO
2CH - Cl 3 + 5CuO → CuCl 2 + 4CuCl + 2CO 2 + H 2 O
A control experiment should be made using a substance that does not contain halogen (benzene, water, alcohol) instead of chloroform. For cleaning, the wire is moistened with hydrochloric acid and calcined.
II. Opening of functional groups. Based on a preliminary analysis (physical properties, elemental analysis), it is possible to approximately determine the class to which a given substance under study belongs. These assumptions are confirmed by qualitative reactions to functional groups.
1. Qualitative reactions to multiple carbon - carbon bonds. a) the addition of bromine. Hydrocarbons containing double and triple bonds easily add bromine:
To a solution of 0.1 g (or 0.1 ml) of the substance in 2 - 3 ml of carbon tetrachloride or chloroform, add dropwise with shaking a 5% solution of bromine in the same solvent. The instant disappearance of the color of bromine indicates the presence of a multiple bond in the substance. But the bromine solution is also decolorized by compounds containing mobile hydrogen (phenols, aromatic amines, tertiary hydrocarbons). However, in this case, a substitution reaction occurs with the release of hydrogen bromide, the presence of which is easily detected using a damp paper of blue litmus or Congo. b) Potassium permanganate test. In a weakly alkaline medium, under the action of potassium permanganate, the substance is oxidized with the breaking of a multiple bond, the solution becomes colorless, and a flocculent precipitate of MnO 2 is formed. - manganese (IU) oxide. To 0.1 g (or 0.1 ml) of a substance dissolved in water or acetone, add dropwise with shaking a 1% solution of potassium permanganate. There is a rapid disappearance of the crimson-violet color, and a brown precipitate of MnO 2 appears. However, potassium permanganate oxidizes substances of other classes: aldehydes, polyhydric alcohols, aromatic amines. In this case, the solutions also become discolored, but the oxidation proceeds for the most part much more slowly.
2. Detection of aromatic systems. Aromatic compounds, unlike aliphatic compounds, are able to easily enter into substitution reactions, often forming colored compounds. Usually, a nitration and alkylation reaction is used for this. Nitration of aromatic compounds. (‘Careful! Thrust!,) Nitration is carried out with nitric acid or a nitrating mixture:
R - H + HNO 3 → RNO 2 + H 2 O
0.1 g (or 0.1 ml) of the substance is placed in a test tube and, with continuous shaking, 3 ml of the nitrating mixture (1 part of concentrated nitrate acid and 1 part of concentrated sulfate acid) is gradually added. The test tube is stoppered with a long glass tube, which serves as a reflux condenser, and heated in a water bath. 5 min at 50 0 C. The mixture is poured into a glass with 10 g of crushed ice. If a solid product or an oil that is insoluble in water and different from the original substance precipitates, then the presence of an aromatic system can be assumed. 3. Qualitative reactions of alcohols. In the analysis for alcohols, substitution reactions are used both for the mobile hydrogen in the hydroxyl group and for the entire hydroxyl group. a) Reaction with metallic sodium. Alcohols readily react with sodium to form alcoholates that are soluble in alcohol:
2 R - OH + 2 Na → 2 RONa + H 2
Place 0.2 - 0.3 ml of anhydrous test substance in a test tube and carefully add a small piece of metallic sodium the size of a millet grain. The evolution of gas upon dissolution of sodium indicates the presence of active hydrogen. (However, acids and CH-acids can also give this reaction.) b) Reaction with cuprum (II) hydroxide. In di-, tri- and polyhydric alcohols, in contrast to monohydric alcohols, freshly prepared cuprum (II) hydroxide dissolves to form a dark blue solution of complex salts of the corresponding derivatives (glycolates, glycerates). Pour a few drops (0.3 - 0.5 ml) of a 3% solution of cuprum (ΙΙ) sulfate, and then 1 ml of a 10% solution of sodium hydroxide. A gelatinous blue precipitate of cuprum (ΙΙ) hydroxide precipitates. The dissolution of the precipitate upon the addition of 0.1 g of the test substance and the change in color of the solution to dark blue confirm the presence of a polyhydric alcohol with hydroxyl groups located at adjacent carbon atoms.
4. Qualitative reactions of phenols. a) Reaction with ferum (III) chloride. Phenols give intensely colored complex salts with ferum (III) chloride. A deep blue or purple color usually appears. Some phenols give a green or red color, which is more pronounced in water and chloroform and worse in alcohol. Place several crystals (or 1 - 2 drops) of the test substance in 2 ml of water or chloroform in a test tube, then add 1 - 2 drops of a 3% ferum (III) chloride solution with shaking. In the presence of phenol, an intense violet or blue color appears. Aliphatic phenols with ferum (ΙΙΙ) chloride in alcohol give a brighter color than in water, and blood-red color is characteristic of phenols. b) Reaction with bromine water. Phenols with free ortho- And pair-positions in the benzene ring easily decolorize bromine water, resulting in a precipitate of 2,4,6- tribromophenol 
A small amount of the test substance is shaken with 1 ml of water, then bromine water is added dropwise. Discoloration of the solution And precipitation of a white precipitate.
5. Qualitative reactions of aldehydes. Unlike ketones, all aldehydes are easily oxidized. The discovery of aldehydes, but not of ketones, is based on this property. a) Silver mirror reaction. All aldehydes easily reduce the ammonia solution of argentum (Ι) oxide. Ketones do not give this reaction:
In a well-washed test tube, mix 1 ml of a silver nitrate solution with 1 ml of a dilute sodium hydroxide solution. The precipitation of argentum (Ι) hydroxide is dissolved by adding a 25% ammonia solution. A few drops of an alcoholic solution of the analyte are added to the resulting solution. The tube is placed in a water bath and heated to 50 0 - 60 0 C. If a shiny deposit of metallic silver is released on the walls of the tube, this indicates the presence of an aldehyde group in the sample. It should be noted that other easily oxidized compounds can also give this reaction: polyhydric phenols, diketones, some aromatic amines. b) Reaction with Fehling's liquid. Fatty aldehydes are capable of reducing divalent cuprum to monovalent:
A test tube with 0.05 g of the substance and 3 ml of Fehling's liquid is heated for 3 - 5 minutes in a boiling water bath. The appearance of a yellow or red precipitate of cuprum (I) oxide confirms the presence of an aldehyde group. b. Qualitative reactions of acids. a) Determination of acidity. Water-alcohol solutions of carboxylic acids show an acid reaction to litmus, congo, or a universal indicator. A drop of a water-alcohol solution of the test substance is applied to a blue wet paper of litmus, congo or a universal indicator. In the presence of acid, the indicator changes its color: litmus becomes pink, Congo blue, and the universal indicator, depending on acidity, from yellow to orange. It should be borne in mind that sulfonic acids, nitrophenols and
some other compounds with a mobile "acidic" hydrogen that do not contain a carboxyl group may also give a color change to the indicator. b) Reaction with sodium bicarbonate. When carboxylic acids interact with sodium bicarbonate, carbon (IY) oxide is released: 1 - 1.5 ml of a saturated solution of sodium bicarbonate is poured into a test tube and 0.1 - 0.2 ml of an aqueous-alcoholic solution of the test substance is added. Isolation of bubbles of carbon(IY) oxide indicates the presence of acid.
RCOOH + NaHCO 3 → RCOONa + CO 2 + H 2 O
7. Qualitative reactions of amines. Amines dissolve in acids. Many amines (especially of the aliphatic series) have a characteristic odor (herring, ammonia, etc.). basicity of amines. Aliphatic amines, as strong bases, are capable of changing the color of indicators such as red litmus, phenolphthalein, and universal indicator paper. A drop of an aqueous solution of the test substance is applied to an indicator paper (litmus, phenolphthalein, universal indicator paper). A change in the color of the indicator indicates the presence of amines. Depending on the structure of the amine, its basicity varies over a wide range. Therefore, it is better to use universal indicator paper. 8. Qualitative reactions of polyfunctional compounds. For qualitative detection of bifunctional compounds (carbohydrates, amino acids), use the complex of the reactions described above.
This substance can be considered not only as an acid, but also as an aldehyde. The aldehyde group is circled in brown.
Therefore, formic acid exhibits the reducing properties typical of aldehydes:
1. Silver mirror reaction:
2Ag (NH3)2OH ® NH4HCO3 + 3NH3 + 2Ag + H2O.
2. Reaction with copper hydroxide when heated:
НСООНa + 2Cu (OH)2 + NaOH ® Na2CO3 + Cu2O¯ + 3H2O.
3. Oxidation with chlorine to carbon dioxide:
HCOOH + Cl2 ® CO2 + 2HCl.
Concentrated sulfuric acid removes water from formic acid. This produces carbon monoxide:
In the molecule of acetic acid there is a methyl group, the rest of the saturated hydrocarbon - methane.
Therefore, acetic acid (and other saturated acids) will enter into radical substitution reactions characteristic of alkanes, for example:
CH3COOH + Cl2 + HCl
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C 6 H 5 -CHO + O 2 ® C 6 H 5 -CO-O-OH
The resulting perbenzoic acid oxidizes the second molecule of benzoic aldehyde to benzoic acid:
C 6 H 5 -CHO + C 6 H 5 -CO-O-OH ® 2C 6 H 5 -COOH
Experiment No. 34. Oxidation of benzoic aldehyde with potassium permanganate
Reagents:
benzoic aldehyde
Potassium permanganate solution
Ethanol
Progress:
Place ~3 drops of benzaldehyde in a test tube, add ~2 ml of potassium permanganate solution and heat on a water bath with shaking until the smell of aldehyde disappears. If the solution does not discolor, then the color is destroyed with a few drops of alcohol. The solution is cooled. Crystals of benzoic acid fall out:
C 6 H 5 -CHO + [O] ® C 6 H 5 -COOH
Experiment No. 35. The oxidation-reduction reaction of benzaldehyde (Cannizzaro reaction)
Reagents:
benzoic aldehyde
Alcoholic solution of potassium hydroxide
Progress:
Add ~5 ml of a 10% alcoholic solution of potassium hydroxide to ~1 ml of benzoic aldehyde in a test tube and shake vigorously. In this case, heat is released and the liquid solidifies.
The redox reaction of benzoic aldehyde in the presence of alkali proceeds according to the following scheme:
2C 6 H 5 -CHO + KOH ® C 6 H 5 -COOK + C 6 H 5 -CH 2 -OH
The potassium salt of benzoic acid (a product of the oxidation of benzoic aldehyde) and benzyl alcohol (a product of the reduction of benzoic aldehyde) are formed.
The resulting crystals are filtered off and dissolved in a minimum amount of water. When ~1 ml of a 10% hydrochloric acid solution is added to a solution, free benzoic acid precipitates:
C 6 H 5 -COOK + HCl ® C 6 H 5 -COOH¯ + KCl
Benzyl alcohol is in the solution remaining after separation of the crystals of the potassium salt of benzoic acid (the solution has the smell of benzyl alcohol).
VII. CARBOXY ACIDS AND THEIR DERIVATIVES
Experience No. 36. Oxidation of formic acid
Reagents:
Formic acid
10% sulfuric acid solution
Potassium permanganate solution
Barite or lime water
Progress:
~0.5-1 ml of formic acid, ~1 ml of 10% sulfuric acid solution and ~4-5 ml of potassium permanganate solution are poured into a test tube with a gas outlet tube. The gas outlet tube is immersed in a test tube with a solution of lime or barite water. The reaction mixture is gently heated by placing boiling stones in a test tube for uniform boiling. The solution first turns brown, then discolors, carbon dioxide is released:
5H-COOH + 2KMnO 4 + 3H 2 SO 4 ® 5HO-CO-OH + K 2 SO 4 + 2MnSO 4 + 3H 2 O
HO-CO-OH ® CO 2 + H 2 O
Experience No. 37. Recovery of an ammonia solution of silver hydroxide with formic acid
Reagents:
Ammonia silver hydroxide solution (Tollens' reagent)
Formic acid
