Experience 10. Obtaining acetylene and its chemical properties

Reagents and equipment: calcium carbide (pieces), saturated bromine water, 1% potassium permanganate solution, 10% sodium carbonate solution, 1% silver nitrate solution, 5% ammonia solution, ammoniacal copper (I) chloride solution; vent tubes, straight vent tubes with drawn end, crucible lids, filter paper, test tubes.

10.1. Obtaining acetylene and its combustion (thrust). A small piece of calcium carbide CaC 2 is placed in a test tube and 1 ml of water is added. The test tube is immediately closed with a cork with a gas outlet tube with a drawn end. The released acetylene is ignited. It burns with a smoky flame (a soot stain forms on the crucible lid brought to the flame). With an intensive supply of oxygen, acetylene burns with a luminous flame, since its complete combustion occurs.

10.2. Reaction of acetylene with bromine water. The test tube with calcium carbide and water is closed with a cork with a curved gas outlet tube and acetylene is passed through saturated bromine water. Observe the gradual discoloration of bromine water.

Explain why acetylene decolorizes bromine water much more slowly than ethylene and confirm with the reaction equation.

10.3. Acetylene oxidation reaction with potassium permanganate. 1 ml of a potassium permanganate solution is poured into a test tube, 1 ml of a 10% sodium carbonate solution is added, and then acetylene is passed through the resulting solution. The violet color disappears and a flocculent precipitate of brown manganese (IV) oxide appears. Write the equation for the oxidation of acetylene and name the reaction products.

10.4. Preparation of silver and copper acetylides. Hydrogen atoms in acetylene, in contrast to ethylene hydrocarbons, can be easily replaced by metals to form the corresponding salts. Similar properties are also characteristic of monoalkyl-substituted acetylene series.

To obtain silver acetylenide, 2 ml of a 1% solution of silver nitrate is poured into a test tube and a 5% solution of ammonia is added dropwise until the precipitate of silver oxide (I) formed at the beginning is completely dissolved. Acetylene is passed through the resulting solution and a yellowish-gray precipitate of silver acetylenide is observed.

To obtain copper (I) acetylenide, 2-3 ml of an ammonia solution of copper (I) chloride is poured into a test tube and acetylene is passed through it. The colorless solution first turns red, and then a red-brown precipitate of copper (I) acetylenide precipitates.

This reaction can be carried out in another way. To do this, moisten a strip of filter paper with an ammonia solution of copper (I) chloride and bring it to the opening of the test tube from which acetylene is released. A reddish-brown color is observed. This very sensitive reaction is used to detect traces of acetylene, including in the sanitary examination of air at enterprises. Write schemes for obtaining acetylides and explain their formation. What properties does acetylene exhibit in this reaction?

Lab #5

AROMATIC COMPOUNDS

BENZENE AND ITS HOMOLOGIES

Experience 11. Obtaining benzene from sodium benzoate

Reagents and equipment: sodium benzoate, caustic soda; ice, curved gas tubes, mortars, glass rods, 100 ml beakers, test tubes.

In a mortar, carefully grind 1 g of sodium benzoate and 2 g of caustic soda. The mixture is placed in a dry test tube, closed with a stopper with a curved gas outlet tube, and the test tube is fixed in the leg of a tripod with an inclination towards the stopper. The end of the gas outlet tube is lowered into a receiver tube cooled with ice water. The tube with the mixture is first uniformly heated on a gas burner, and then the part of the tube filled with the reaction mixture is strongly heated. The resulting benzene is collected in a receiver tube. It is detected by smell and flammability. To do this, a glass rod is moistened with the resulting distillate and brought to the flame of the burner. Benzene burns with a smoky flame.

Experience 12. The ratio of aromatic hydrocarbons to oxidizing agents

Reagents and equipment: benzene, toluene, 5% potassium permanganate solution, 10% sulfuric acid solution; reflux condensers for test tubes, water baths.

Pour 1 ml of benzene and toluene into two test tubes and add 1 ml of 5% potassium permanganate solution and 10% sulfuric acid solution to each. The tubes are stoppered with air coolers and heated in a water bath. In a test tube with toluene, discoloration of potassium permanganate is observed, and in a test tube with benzene, no changes occur. Explain why? Write reaction equations.

It should be noted that benzene may contain impurities that change the color of potassium permanganate, so for the experiment it is necessary to take pre-purified benzene.

Experience 13. Bromination of benzene(thrust)

Reagents and equipment: benzene, a solution of bromine in carbon tetrachloride (1:5), iron filings, blue litmus paper; water baths, reflux condensers for test tubes, test tubes.

1 ml of benzene and 1 ml of a solution of bromine in carbon tetrachloride are poured into two test tubes. A little iron filings are added to one of the test tubes (on the tip of a spatula). The tubes are stoppered with air coolers and heated in a warm water bath. After some time in a test tube with iron filings, the reaction mixture becomes colorless. A blue litmus paper moistened with water and brought to the free ends of glass tubes confirms that the reaction takes place only in a test tube with iron filings (the color of the indicator changes from the vapors of released hydrogen bromide).

After 5-10 min after the start of the reaction, a strip of filter paper is lowered into the reaction mixture, which is then dried in air. Bromobenzene remains on the paper, which differs in smell from the original benzene.

It must be remembered that the hydrogen substitution reaction in benzene occurs in the presence of an activated halogen particle. Halogen activation is carried out by the action of catalysts (often Lewis acids). Halogenation into the core proceeds by the mechanism of electrophilic substitution (SE).

Write the reaction equation for the formation of an aprotic Lewis acid (FeBr 3) and the mechanism of the benzene bromination reaction. Which of the isomers of dibromobenzene can be obtained by further bromination of bromobenzene?

Experience 14. Bromination of toluene(thrust)

Reagents and equipment: toluene, a solution of bromine in carbon tetrachloride, iron filings, blue litmus paper; reflux condensers for test tubes, water baths, test tubes.

Experiment 13 is repeated, but instead of benzene, 1 ml of toluene is added to two test tubes. A test tube containing no iron filings is heated in a boiling water bath.

Unlike the previous experiment, the reaction proceeds in both test tubes. Bromination of toluene proceeds in two directions, depending on the reaction conditions. In the absence of a catalyst (Fe), but when heated, the halogen replaces the hydrogen in the side chain by a radical mechanism (S R).

In the presence of a catalyst (Lewis acid), hydrogen is replaced by bromine in the aromatic nucleus by the ionic mechanism (SE), while the halogen atom enters the ring in the ortho or para position with respect to the alkyl radical.

Write the mechanisms of toluene halogenation into the side chain (S R) and into the aromatic ring (S E). Explain the role of a catalyst in the halogenation of aromatic hydrocarbons into a ring. Explain the orienting effect of alkyl radicals in electrophilic substitution reactions in terms of static and dynamic approaches.

Experience 15. Nitration of benzene(thrust)

Reagents and equipment: benzene, concentrated nitric and sulfuric acids; reflux condensers for test tubes, water baths, 50 ml beakers, ice, test tubes.

1 ml of concentrated nitric acid (r = 1.4 g / cm 3) and 1.5 ml of concentrated sulfuric acid are added to the test tube. The nitrating mixture is cooled with ice water, and then, with shaking and cooling, 1 ml of benzene is added in several steps. The tube is stoppered with an air condenser and heated in a water bath (50-55 °C) for 5-10 minutes, shaking occasionally. After completion of the reaction, the contents of the test tube are carefully poured into a glass of ice water. Excess mineral acids dissolve in water, and nitrobenzene is released at the bottom of the glass in the form of oily yellowish drops, smelling of bitter almonds.

Write the mechanism of the benzene nitration reaction. What role does sulfuric acid play?

Experience 16. Sulfonation of benzene and toluene(thrust)

Reagents and equipment: benzene, toluene, concentrated sulfuric acid; reflux condensers for test tubes, water baths, 50 ml beakers, test tubes.

0.5 ml of benzene and toluene are placed in test tubes and 2 ml of concentrated sulfuric acid are added. The tubes are closed with stoppers with air coolers and heated in a boiling water bath for 10-15 minutes with constant stirring. Toluene gradually dissolves in sulfuric acid, but no changes occur in a test tube with benzene. When the toluene is completely dissolved, the tubes are cooled, and their contents are carefully poured into beakers with 20 ml of water. Benzene floats to the surface of the water, since under these conditions it does not react with sulfuric acid. Toluene is sulfonated more easily than benzene. During the reaction, isomeric toluenesulfonic acids are formed, which are readily soluble in water.

Explain how the alkyl radical affects the rate of the sulfonation reaction in an aromatic ring. Write the reaction mechanism for the sulfonation of toluene.

When a mixture of propane and acetylene was passed through a flask with bromine water, the mass of the flask increased by 1.3 g. With complete combustion of the same amount of the initial mixture of hydrocarbons, 14 l (N.O.) of carbon monoxide (IV) were released. Determine the mass fraction of propane in the initial mixture.

Solution: Acetylene is absorbed by bromine water:

HC ≡ CH + 2Br 2 → NSVr 2 -SNVr 2.

1.3 g is the mass of acetylene. v (C 2 H 2) \u003d 1.3 / 26 \u003d 0.05 mol. During the combustion of this amount of acetylene according to the equation

2C 2 H 2 + 5O 2 \u003d 4CO 2 + 2H 2 O

2-0.05 \u003d 0.1 mol CO 2 was released. The total amount of CO 2 is 14/22.4 = 0.625 mol. When propane is burned according to the equation

C 3 H 8 + 5O 2 \u003d ZSO 2 + 4H 2 O

0.625 - 0.1 \u003d 0.525 mol CO 2 was released, while 0.525 / 3 \u003d 0.175 mol C 3 H 8 with a mass of 0.175 - 44 \u003d 7.7 g entered into the reaction.

The total mass of the mixture of hydrocarbons is 1.3 + 7.7 = 9.0 g, and the mass fraction of propane is:  (C 3 H 8) = 7.7 / 9.0 = 0.856, or 85.6%.

Answer. 85.6% propane.

Setting up experiments and text– Ph.D. Pavel Bespalov.

The interaction of acetylene with chlorine

We pour a small amount of potassium permanganate crystals into the cylinder and throw a piece of calcium carbide. Then pour hydrochloric acid into the cylinder. Flashes are observed in the vessel, the walls of the cylinder are covered with soot. When hydrochloric acid reacts with potassium permanganate, chlorine gas is released

16 HCI + 2KMnO 4 = 5CI 2 + 2 KCI + 2 MnCI 2 + 8H 2 O

FROM hydrochloric acid calcium carbide gives acetylene

CaC 2 + 2HCI\u003d C 2 H 2 + CaCI 2

Chlorine reacts with acetylene to form hydrogen chloride and charcoal.

C 2 H 2 + CI 2 \u003d 2C + 2 HCI

Equipment: cylinder, spatula.

Safety engineering. Observe the rules for working with combustible gases. The experiment is carried out only under traction. After the experiment, fill the cylinder with water.

Reaction of ethylene with bromine water

Ethylene is obtained by heating a mixture of ethanol and concentrated sulfuric acid. The released ethylene is passed through a solution of bromine in water, which is called bromine water. Bromine water becomes colorless very quickly. Bromine adds to ethylene at the double bond. In this case, 1,2-dibromoethane is formed.

CH 2 \u003d CH 2 +Br 2 = CH 2 Br — CH 2 Br

The decolorization reaction of an aqueous solution of bromine serves as a qualitative reaction to the unsaturation of organic compounds.

Equipment:

Safety engineering.

Reaction of acetylene with bromine water

Acetylene is produced by the action of water on calcium carbide. Pass the acetylene released through bromine water. We observe the discoloration of bromine water. Bromine adds to acetylene at the site of the triple bond. In this case, a compound with four bromine atoms in the molecule is formed - 1,1,2,2-tetrabromoethane.

CH ≡ CH + 2Br 2 = CHBr 2 — CHBr 2

The decolorization of bromine water proves the unsaturation of acetylene.

Equipment: Wurtz flask, separating funnel, vent tube, beaker or test tube, tripod.

Safety engineering. The experiment should be carried out under traction. Observe the rules for working with combustible gases.

The interaction of acetylene with a solution of potassium permanganate

Acetylene is produced by the action of water on calcium carbide. When passing acetylene through an acidified solution of potassium permanganate, we observe a rapid discoloration of the solution. Acetylene is oxidized at the site of triple bond rupture with the formation of an oxidation product, oxalic acid. In excess of potassium permanganate, oxalic acid is oxidized to carbon dioxide and water.

The discoloration of the potassium permanganate solution is proof of the unsaturation of acetylene.

Equipment: Wurtz flask, separating funnel, vent tube, beaker, tripod.

Safety engineering. Observe the rules for working with combustible gases.

Interaction of ethylene with a solution of potassium permanganate.

Ethylene is obtained by heating a mixture of ethanol and concentrated sulfuric acid. We lower the gas outlet tube with ethylene released into an acidified solution of potassium permanganate. The solution quickly decolorizes. In this case, ethylene is oxidized to the dihydric alcohol ethylene glycol.

CH 2 \u003d CH 2 + [O] + H-OH \u003dCH 2 HE -CH 2 HE

This reaction is a qualitative double bond reaction.

Equipment: Wurtz flask, dropping funnel, washer, vent tube, beaker or test tube, tripod.

Safety engineering.

Observe the rules for working with flammable gases, concentrated acids and flammable liquids.

Explosion of a mixture of acetylene and oxygen

A mixture of acetylene and oxygen explodes with great force when ignited. Therefore, it is safe to experiment only with small volumes of the mixture - a soap solution will help us with this. In a porcelain mortar with water and a solution of soap, add a little hydrogen peroxide. Add a catalyst, manganese dioxide, to the resulting solution. Immediately begins the release of oxygen.

2H 2 O 2 \u003d 2H 2 O + O 2

Dip a small piece of calcium carbide into this mixture. When reacted with water, it gives acetylene.

CaC 2 + 2 H 2 O \u003d C 2 H 2 + Ca (OH) 2

On the surface of the solution, due to the presence of soap, bubbles are formed, filled with a mixture of acetylene and oxygen. When the bubbles are ignited, strong explosions of a mixture of acetylene and oxygen occur.

Equipment: porcelain mortar, splinter.

Safety engineering. Observe the rules for working with combustible gases. Only a small amount of the mixture can be ignited.

Burning acetylene

We get acetylene from calcium carbide and water. We close the flask with a cork with a gas outlet tube. An injection needle is inserted into the end of the gas outlet tube. After some time, when the acetylene completely displaces the air from the flask, we set fire to the gas released. Acetylene burns with a bright white flame. The combustion of acetylene produces carbon dioxide and water.

2CH ≡ CH + 5O 2 → 4CO 2 + 2H 2 O

Let's bring the test tube into the flame of burning acetylene. Soot settles on the test tube. With a lack of oxygen, acetylene does not have time to completely burn out and releases carbon in the form of soot. The luminosity of the flame is explained by the high percentage of carbon in acetylene and the high temperature of its flame, in which unburned carbon particles are heated.

Equipment: round bottom flask, stopper with a needle from a medical syringe, tripod.

Safety engineering. Observe the rules for working with combustible gases. It is possible to set fire to acetylene only after sampling for purity.

Ethylene burning

Ethylene is obtained by heating a mixture of ethanol and concentrated sulfuric acid. The mixture is prepared from one part of alcohol and three parts of sulfuric acid. Sulfuric acid acts as a dehydrating agent. When the mixture is heated, ethylene is released.

C 2 H 5 OH \u003d C 2 H 4 + H 2 O

We collect ethylene in the cylinder by displacing water. Ethylene is a colorless gas, slightly soluble in water. Ethylene burns in air to form carbon dioxide and water.

C 2 H 4 + 3O 2 \u003d 2CO 2 + 2H 2 O

Equipment: Wurtz flask, separating funnel, washer, vent tube, tripod, cylinder.

Safety engineering. Observe the rules for working with flammable gases, concentrated acids and flammable liquids.

Obtaining copper acetylenide

Acetylene is produced by the action of water on calcium carbide. The hydrogen atoms in the acetylene molecule are highly mobile. Therefore, they can easily be replaced by metals. Let's pass acetylene through an ammonia solution of copper (I) chloride. A red precipitate of copper(I) acetylenide precipitates.

CH ≡ CH + 2CuCI → CuC ≡ CCu ↓ + 2 HCI

Equipment:

Safety engineering. Observe the rules for working with combustible gases. Receive only small amounts of copper acetylenide. Dried copper acetylenide is a very dangerous explosive. It is destroyed by treatment with concentrated hydrochloric acid.

Obtaining silver acetylenide

Acetylene is produced by the action of water on calcium carbide. The hydrogen atoms in the acetylene molecule are highly mobile. Therefore, they can easily be replaced by metals. Pass acetylene through an ammonia solution of silver oxide. Silver acetylenide precipitates.

CH ≡ CH + Ag 2 O → AgC ≡ CAg ↓ + H 2 O

Equipment: Wurtz flask, separating funnel, vent tube, beaker or test tube, polypropylene funnel, filter paper, tripod.

Safety engineering. Observe the rules for working with combustible gases. Receive only small amounts of silver acetylide. Dried silver acetylenide is a very dangerous explosive. It is destroyed by treatment with concentrated hydrochloric acid.

Fragility of metal acetylides

Metal acetylides are unstable compounds. When wet, silver acetylenide is stable; when dried, it explodes easily. We bring a smoldering splinter to dry silver acetylenide - it explodes. Let's carry out a similar experiment with copper (I) acetylenide. Like silver acetylenide, copper(I) acetylenide is stable when wet, but decomposes easily when dried. A burning splinter brought to dry copper (I) acetylenide leads to an explosion. This produces a green flame.

Equipment: fire-retardant gasket, splinter.

Safety engineering. Only small amounts of silver and copper acetylenide can be obtained and decomposed. Dried silver and copper acetylenides are dangerous explosives. The acetylenides are destroyed by treatment with concentrated hydrochloric acid.

Experiments on the production of acetylene and the study of its properties are demonstrated simultaneously. It is not necessary to prepare acetylene for the lesson in advance and store it in the gasometer due to the risk of explosion.

^ Getting acetylene. The most affordable way to obtain acetylene is the interaction of calcium carbide with water:

CaC 2 + 2H 2 O  C 2 H 2 + Ca (OH) 2

The flask for the reaction should not be taken too small, since during the reaction the resulting thick liquid swells and the foam can be driven by gas through the outlet tube. If too large a flask is used, it will take a long time until all the air is expelled from the device, and if you wait for this moment, then there will be a large loss of acetylene. It is convenient to use a flask with a capacity of 250 ml. In the case of using a flask of a larger capacity, experiments with acetylene can be started with reactions that do not require air displacement, which will make it possible to carry out them quite economically.

When water is added to calcium carbide, the reaction is always very violent; acetylene is therefore consumed involuntarily, and it may not be enough to show all the planned experiments. There are two ways to get a calmer and more uniform current of acetylene: add ethyl alcohol to calcium carbide and only then start up water, or use a saturated solution of common salt instead of water.

7-8 pieces of calcium carbide the size of a pea are placed in the flask, a stopper with a funnel is inserted tightly, a saturated solution of sodium chloride is poured into the funnel and a few drops are put into the flask. Further addition of the solution is carried out in such a way that a uniform flow of gas is established at a speed that allows one to count the bubbles. Draw the attention of students to the fact that the reaction, in contrast to the production of ethylene and methane, goes without heating.

The resulting gas is collected in cylinders by the method of water displacement (after checking for the completeness of air displacement) or directly used for the corresponding experiments. In view of the noticeable solubility of acetylene in water, it is sometimes recommended to collect it over a solution of table salt, however, as experience shows, it is quite possible to use ordinary water.

^ Dissolution of acetylene in water . Acetylene is more soluble in water than methane and ethylene.

1. Pass acetylene through water in a test tube for several minutes. After that, the water is heated to a boil and a lighted splinter is brought to the test tube opening. The acetylene released from the water flares up.

2. A cylinder or test tube with pure (without air) acetylene is overturned with a hole into a glass with tinted cold water. When the cylinder (tube) is shaken, the water level in it rises noticeably. This phenomenon will be more evident if the cylinder is fixed in a tripod in this position and left until the next lesson.

^ Dissolving acetylene in acetone . Acetylene is highly soluble in acetone. In the form of such a solution, it is usually stored in steel cylinders (with a porous filler).

Pour 3-4 ml of acetone into a small cylinder with acetylene. The cylinder is closed with a cork, shaken several times and thrown into a bath of colored water. When the plug is opened, water rises in the cylinder.

^ Burning acetylene . The complete combustion of acetylene is expressed by the equation:

2C 2 H 2 + 5O 2  4CO 2 + 2H 2 O

The external picture of combustion and the temperature developed in this case depend to a large extent on the volumetric ratio of gases.

The acetylene collected in the cylinder is ignited according to the method of water displacement. The gas burns with a smoky flame. As the flame moves inside the cylinder, the formation of soot intensifies, since combustion in the cylinder proceeds with an even greater lack of oxygen. The acetylene is ignited and, at the outlet tube of the device (Fig. 14), attention is paid to the fact that the smaller the opening of the tube, the gas burns with a less sooty flame, and complete combustion occurs in a thin stream of gas.

^ Explosion of acetylene with oxygen . A mixture of acetylene and oxygen, when ignited, explodes with great force. Therefore, the experiment can be carried out in a steel cylinder or in such a shell, the rupture of which is not dangerous. It is best to show the explosion of acetylene in soap bubbles.

In soapy water, prepared in advance in an iron cup at the rate of 1 g of soap per 30-40 ml of water and 4-5 ml of glycerin, acetylene from the device and oxygen from the gasometer are simultaneously passed. They take away the instruments from the table and set fire to the formed bubbles with a mixture of gases with a long splinter. There is a strong but harmless explosion.

^ Reaction of acetylene with bromine and potassium permanganate solution. Experiments illustrating the unsaturation of acetylene can be carried out in two ways: a) by passing acetylene into bromine water and a solution of potassium permanganate, b) by pouring these solutions into cylinders with acetylene.

When demonstrating experiments in the first way, the discoloration of solutions (especially bromine water) occurs rather slowly. Stirring the solutions with a glass rod somewhat speeds up the process.

When demonstrating experiments in the second way, the gas with solutions in the cylinders is shaken; discoloration occurs faster.

Based on the structure of acetylene, students usually correctly formulate the equations for its reactions with bromine:

The reaction of acetylene with potassium permanganate, like the reaction of ethylene, can only be considered here in general terms.

If the reaction of acetylene with bromine and potassium permanganate is demonstrated by passing gas through solutions, then the time it takes for solutions to become colorless (compare with ethylene) can be used to analyze the reaction. Such an experiment should be carried out under draft, since a relatively large amount of acetylene (with toxic impurities) is released into the atmosphere. The discussion of the experiment can be started something like this: “Based on the presence of a triple bond in the acetylene molecule, we suggest that it should be easily oxidized and enter into addition reactions. By what sign can we determine whether these reactions will go in the experiment? After the students answer, the teacher poses the question: “If there is a discoloration of the solutions, then how could these reactions be expressed by equations?”

^ Burning acetylene in chlorine . Acetylene, like other hydrocarbons, burns in chlorine to form hydrogen chloride and coal:

C 2 H 2 + CI 2  2C + 2HCI

1. A curved glass tube with burning acetylene is slowly introduced into the chlorine cylinder. Acetylene continues to burn in chlorine, forming soot. You can fill the cylinder with chlorine during the lesson by pouring a little crushed potassium permanganate into it and pouring in concentrated hydrochloric acid.

2. A curved tube is gradually introduced into the cylinder with chlorine, through which acetylene flows (preliminarily checked for chi-

Stotu). Acetylene ignites in chlorine. Experience illustrates the great chemical activity of acetylene.

3. Pour some bleach into a glass cylinder and douse it with dilute hydrochloric acid. A few pieces of calcium carbide are also thrown there. After some time, flashes of flame are observed in the cylinder, then fading, then reappearing and rolling from top to bottom.

When bleach reacts with acid, chlorine is released:

CaCIOCl + 2HCI  CaCI 2 + H 2 O + CI 2

and in the reaction of calcium carbide with water - acetylene (eat p. 51). Acetylene and chlorine enter into an addition reaction, from the heat of which acetylene ignites in chlorine (in the cylinder) and in air (at the cylinder bore). Bleach is taken here because it forms chlorine when it reacts with dilute hydrochloric acid, while potassium permanganate releases it when it reacts with dilute hydrochloric acid. concentrated acid. The presence of free water is necessary to obtain a sufficiently large amount of acetylene.

^ Experiments with PVC . When familiarizing yourself with polyvinyl chloride, you should consider its relationship to heat, to chemicals and solvents. The last two experiments are not described here, since they are set up in the same way as with polyethylene.

A) Pieces of vinyl plastic or PVC film (oilcloth, insulation) are heated carefully in a test tube or porcelain cup.

Make sure that the polymer does not go into a liquid state, but decomposes. Wet litmus paper is brought to the evolved gaseous decomposition products and then a stick moistened with an ammonia solution. The reddening of the paper is observed in the first case and the formation of a white haze in the second. They conclude that hydrogen chloride is released during the decomposition of polyvinyl chloride.

B) Pieces of PVC are heated in a test tube, closed with a stopper with a drain tube. The gaseous decomposition products are taken into a test tube with water. To received aqueous solution pour a little solution of silver nitrate and 1-2 drops of nitric acid. The formation of a precipitate of silver chloride is observed, which indicates the release of hydrogen chloride during the decomposition of the polymer.

Development of a lesson in chemistry

Grade 10

Lesson 8

Lesson topic: Alkynes. Acetylene, its production by methane pyrolysis and carbide method. Chemical properties acetylene: combustion, discoloration of bromine water, addition of hydrogen chloride and hydration. Application of acetylene based properties. Vinyl chloride polymerization reaction. Polyvinyl chloride and its application.

Lesson Objectives:

- Exploregeneral formula, nomenclature, physical properties of representatives of the homologous series of alkynes, their structure, chemical properties of the first representative of the homologous series of alkynes - acetylene, application.

- Develop general educational competencies, logical thinking.

Raise students' curiosity,show the importance of knowledge of organic chemistry.

Lesson type: UPNZ

Information and methodological support: slides, diagrams, collection materials, tables on the topic of the lesson.

Textbook: Chemistry. Organic chemistry. Grade 10 (basic level).Rudzitis G.E., Feldman F.G.,15th ed. - M.: 2012. - 192 p.

Characteristics of students' activities: frontal, individual, work at the board.

Types of control: Interview.

During the classes

I. Organizational moment of the lesson

II. Knowledge update

Survey on basic concepts:

hydrocarbons

Saturated and unsaturated compounds

Alkynes: formula of the series, the first representative of the series, basic properties, methods of preparation, application.

III. Checking homework

IV. Presentation of new material

Alkynes - unsaturated hydrocarbons, the molecules of which, in addition to single C-C- ties contain one triple C≡ C-bond.

The general formula of the series isFROM n H 2n-2

Features of the alc nomenclature and new

The belonging of a hydrocarbon to the class of alkenes is reflected by the suffix–in:

FROM 2 H 2 CH≡ CHethyne (acetylene)

FROM 3 H 4 CH≡ C-CH 3 propyne

FROM 4 H 6 CH≡ C-CH 2 -CH 3 butin-1

etc.

The rules for naming compounds remain the same as for alkenes, only the suffix is ​​replaced by–in .

Isomerism of alkenes

Structural isomerism.

1. Isomerism of the structure of the carbon chain.

   Isomerism of the position of the triple bond.

   Interclass isomerism.

Give examples of isomers of each type, name them!

Features of the structure of molecules (for example, acetylene)

In acetylene, carbon is in the statesp - hybridization(hybridization involves onesand 1p-orbital). Each carbon atom in the ethylene molecule has 2 hybridsp - orbitals and two non-hybrid p-orbitals. The axes of hybrid orbitals are located in the same plane, and the angle between them is 180 °. Such orbitals of each carbon atom intersect with those of another carbon atomands-orbitalstwo water conduit atoms, formingσ -C-C and C-H bonds.

Education scheme σ-bonds in a molecule ace tylena

The four non-hybrid p-orbitals of carbon atoms overlap in mutually perpendicular planes that are perpendicular to the planeσ -connections. Thus two are formedπ- connections.

FROM ≡ C = σ + 2 π

Scheme of the formation of π-bonds in a molecule uh tylena

The structure of the acetylene molecule

Physical Properties

Acetylene is a gas, lighter than air, slightly soluble in water, odorless. Forms explosive mixtures with air.

In the alkyne series, the boiling point increases with increasing molecular weight.

Describe the physical properties of acetylene in the form of a table in your notebook!

Receipt

Methods for obtaining acetylene:

Made of calcium carbide. (Laboratory method)

CaS 2 + 2H 2 O → S 2 H 2 + Ca(OH) 2

Obtaining calcium carbide (in industry):

CaO + 3C CaC 2 + CO

calcium oxide coke calcium carbide

CaCO 3 CaO+CO 2

calcium carbonate calcium oxide

Thermal decomposition of methane.

2CH 4 FROM 2 H 2 + 3H 2

Methods for obtaining homologues of acetylene - hydrocarbons of a number of alkynes:

Dehydrohalogenation - elimination of two hydrogen halide molecules from dihaloalkanes, which contain two halogen atoms either on adjacent or on one carbon atom:

The reaction proceeds under the action of an alcoholic solution of alkalis on halogen derivatives.

2 H 5 HE

CH 3 - SWr 2 - CH 3 + 2KOH

CH 3 -C ≡ CH + 2KVr+ 2H 2 O,

2,2 - dibromopropane propyne

Chemical properties

Addition reactions

1. Interaction with halogens

A qualitative reaction to the presence of multiple bonds is the discoloration of bromine water!

The addition reactions proceed in two stages.

acetaldehyde

1. With metals.

The reaction product - acetylenides - poorly soluble, unstable, explosive substances!

The formation of a grayish-white precipitate of silver acetylenide or a red-brown precipitate of copper acetylenide is a qualitative reaction to the terminal triple bond!

Oxidation reactions.

1. Combustion.

Acetylene can polymerize to benzene and vinyl acetylene.

Polymerization of vinyl chloride



Polyvinyl chloride (PVC) is used to produce durable plastic, artificial leather, oilcloth, dielectrics, etc.

Application of acetylene

Raw materials in organic synthesis (production of fibers, dyes, varnishes, medicines, PVC, chloroprene rubber, acetic acid, solvents, etc.)

When cutting and welding metals.

V. Consolidation of knowledge.

Solving problems and exercises

p.54 - exercise 1,3,5,6.

p.55 - exercise 8

p.55 - tasks 1.

V I . Reflection. Summing up the lesson

VI I . Homework

paragraph 13,

With. 55 - tasks 2, 3

Explain the differences between the structure of ethylene and acetylene molecules.

What hydrocarbon is the closest homologue of ethine?

Make up the reaction equations with which you can carry out the following transformations, indicate the conditions for the reactions to occur, name the reaction products: