Drying organic liquids. Preparation of calcium carbide - Chemistry for the curious

The most common dehydrating agent for organic liquids containing small amounts of water is calcined calcium chloride.

Alcohols and amines cannot be dried with calcium chloride.

Calcium chloride CaCl2 must be dehydrated before work by calcining it in an iron frying pan. The salt is poured in a layer no thicker than 1-2 cm and heated with a strong burner flame. First, the salt melts, releasing water of crystallization, and then the latter gradually evaporates. Water vapor breaking through the layer of salt causes it to scatter; Therefore, it is not recommended to pour a thick layer of salt. When all the water has evaporated, calcination is continued for some time, then the baked salt is broken into smaller pieces and, while still warm, placed in a completely dry jar prepared in advance. The jar must be closed hermetically so that air, which always contains a certain amount of water vapor, does not penetrate into it.

If the jar is closed with a cork stopper, then the top should be carefully filled with paraffin or wax.

The laboratory should always have a certain supply of calcined CaCl2.

To dehydrate any organic liquid, one or another amount of CaCl2 is taken depending on the water content in it. You should not take too much salt, as this will inevitably lead to loss of the dehydrated substance. Salt in the required amount is poured into a vessel with the liquid to be dried, the vessel is tightly closed with a stopper and shaken several times. The mixture is then left to stand for at least 12 hours. After this, the liquid is poured into a distillation flask and distilled (see above). Calcium chloride can be used repeatedly if it is reheated after each use. Therefore, in laboratories where you often have to deal with CaCl2, there should be jars into which waste salt should be poured; as it accumulates, it is calcined again. Since this also burns the remains of the liquid that was dried with this salt, the calcination of the used CaCl2 should be carried out somewhat differently than the pure one.

First, the salt is carefully heated until liquid vapors are removed and the heating is gradually increased. Otherwise, a fire may occur, especially if the salt contains residues of ether, acetone or other flammable substances. Calcination should be carried out in a fume hood.

Among other salts, calcined sodium sulfate is used for drying organic liquids. It is calcined in the same way as CaCl2. Sodium sulfate Na2SO4 is not as strong a drying agent as CaCI2.

To dry alcohols, use copper sulfate CuSO4 or calcium oxide CaO. Copper sulfate CuSO4 5H2O in the form of blue crystals contains water of crystallization; If you heat the salt, you get an anhydrous yellowish salt. When humidified, one molecule of salt initially attaches only two molecules of water and turns blue. Knowing the water content in alcohol, you can calculate the amount of CuSO4 required to completely dry it.

After adding CuSO4 to the alcohol, the flask is shaken several times and then heated in a water bath under reflux until the salt turns light blue. After this, having separated the salt by filtration, the alcohol is distilled off.

However, it is very difficult to obtain completely anhydrous, so-called absolute, alcohol. After drying it, CuSO4 alcohol must be distilled two or three more times with pure CaO, and the receiver must be tightly connected to the refrigerator and equipped with a calcium chloride tube with dry calcium chloride.

But even after this, up to 0.5% water remains in the alcohol, the removal of which is the most difficult. Sodium and calcium metals are sometimes used to remove this residue.

The best dehydrating agent for alcohol is magnesium ethoxide, which can be easily obtained by reacting magnesium and ethyl alcohol (the alcohol should contain no more than 1% water) in the presence of a small amount of iodine. Dehydration of alcohol using this method is carried out as follows.

5 g of magnesium shavings are poured into a 1.5 liter flask with a reflux condenser, 65-70 ml of alcohol is poured, 0.5 g of iodine (catalyst) is added and heated until the latter dissolves, after which hydrogen is released:

Mg+ 2C2H5OH -> Mg (OC2H5)2 + H2

When the reaction is over, add 800-900 ml of ordinary absolute alcohol to the solution, i.e., one that contains 0.5-0.7% water, boil for half an hour at reflux and then distill off the absolute alcohol.

Other alcohols, such as methyl and n-propyl, can be dehydrated in the same way.

The alcohol can be dried with calcium metal using a reflux flask. 20 g of dry calcium shavings are added to 1 liter of alcohol and heated in a water bath until boiling, which is maintained for several hours, after which the alcohol is distilled in compliance with all the precautions described above.

Water, benzene and ethyl alcohol form an azeotropic mixture. With the content of ethyl alcohol, water and benzene in the ratio of 18.5: 7.4: 74.1, the mixture boils at 65 0C, which makes it possible to use such a mixture to remove traces of water from alcohol.

To do this, dry benzene is added to ethyl alcohol containing at least 99% C2HsOH. For almost 1 hour of water contained in alcohol, you should take 11 - 12 hours of dry benzene. After this, the mixture is subjected to fractional distillation. The first fraction is distilled at 64.85 ° C and consists of alcohol, water and benzene. The second fraction boils at 68.25° C and consists of excess benzene and alcohol. That part of the ethyl alcohol that remains in the distillation vessel is absolute ethyl alcohol.

Dehydrated alcohol should be very carefully protected from air moisture. Therefore, quickly pour it into a well-dried container and carefully close it. This method can be used to dehydrate all alcohols except methyl alcohol.

The completeness of alcohol dehydration can be determined based on the following qualitative samples:

a) anhydrous alcohol dissolves caustic barite, forming a yellow-colored solution;

b) the paraffin solution does not form turbidity in it;

c) in absolute alcohol, anhydrous copper sulfate does not change its color.

Drying agents are used to dehydrate solid organic compounds (of fructose and especially those substances that can soften, melt or decompose at the temperature required to remove water by direct heating). To do this, the solid is filled with absolute ethyl alcohol, and then benzene is added. Heating is carried out on a water bath. When all the liquid has distilled off, the remaining benzene and alcohol are removed from the flask by blowing dry air

Diethyl ether can be dehydrated with a small amount of sodium metal.

Metallic sodium is stored under a layer of kerosene, petroleum jelly or toluene in jars. The need for such storage of metallic sodium is caused by the following: 1) it oxidizes strongly in air, 2) it must be isolated from water, since if a drop of water gets on it, an explosion may occur. Sodium metal must be handled with care. It is necessary to ensure that there is no water near the work area. Working near a sink or near water taps is completely unacceptable.

Kerosene, petroleum jelly and toluene, in which sodium is stored, must be neutral and, naturally, do not contain water.

This piece is quickly pressed with filter paper and a piece of the required size is cut from it with a clean, dry knife. The remaining portion is immediately put back into the jar.

The cut piece of sodium is pressed again with filter paper so that no kerosene or petroleum jelly remains on it. After this, to remove sodium oxide from the surface of the metal, a thin layer (“crust”) is cut off with a clean, dry knife, and the trimmings are placed in a jar with metallic sodium. The purified piece of sodium is cut with a knife into several smaller pieces about 2 mm3 in size and then quickly placed in ether or other liquid that needs to be dried. The flask must be closed with a stopper and a calcium chloride tube.

After the sodium has been in the liquid to be dried for 12-24 hours, the liquid is distilled off over metallic sodium. When the distillation is complete, the remaining meth< талла переносят в банку с керосином или вазелиновым маслом. Лучше иметь отдельную банку, куда следует класть как обрезки («корочки»), так и металл, уже упо-треблявшийся для работы.

It is also recommended to store sodium metal (and potassium) in plastic wrap. The sodium is placed in a bag of polyethylene film having a thickness of 0.5 mm (this thickness can be achieved by putting several layers of ordinary plastic film together), the open end of the bag is sealed. If you need to take a certain amount of sodium, the bag is opened, the substance is pushed out of it, a piece is cut off with a clean knife and the remaining part is pushed back into the bag, the edges of which are first bent so that no air enters it, and then sealed. The sodium trimmings can be placed in the same or another bag and sealed by sealing.

Scraps and spent pieces of sodium metal can be reused if they are melted down. The melting point of sodium metal is 98°C. Sodium cannot be melted in the open air. Therefore, it is melted in a liquid that is not affected by metallic sodium and which boils at a temperature not lower than 150 ° C. Kerosene can serve as such a substance, but even better, i.e. safer, is Vaseline oil. Having placed the trimmings and pieces of sodium in one of these liquids, the latter is heated to approximately 12O0C. The metallic sodium is melted and at the bottom of the porcelain cup in which the heating takes place, a piece of metal with a clean surface is formed. If melting produces separate balls of metal, they are connected by using a thin glass rod. When all the metal has fused, the liquid is allowed to cool, then it is carefully drained (but not all), and the sodium is grabbed with dry tweezers and placed in kerosene.

Organic liquids can also be dried using calcium carbide CaCr. Calcium carbide decomposes with water to form acetylene and calcium hydroxide:

CaC2 + 2H2O = C2H2 + Ca(OH)2

The use of calcium carbide for drying is possible only in cases where the liquid being dried does not react with CaC2, C2H2, or Ca(OH)2. Since when drying with calcium carbide a gas (acetylene) is released, the flask where the drying is carried out must be closed with a stopper with a calcium chloride tube.

Drying is either carried out directly by pouring pure powdered CaC2 into the liquid to be dried (in an amount of up to 10-15% of the mass of the taken liquid, depending on the water content), or the liquid vapor is dried. *

To dry liquid vapors with calcium carbide, install a device consisting of a flask, a reflux condenser and a bath. Pour the dried substance into the flask and strengthen it in the bath. In a ball refrigerator, a fine metal mesh is placed between the second and third or third and fourth balls; CaC2 pieces of such a size are carefully thrown into the refrigerator that they freely pass through its tube. Having filled two or three balls in this way, strengthen the condenser in the neck of the flask and heat it. Vapors of a substance containing water pass through the CaC2 layer and, upon cooling and condensation, the dehydrated substance flows into the flask. Dehydration is carried out for 2-3 hours, and the end can be judged by the fact that the powder or lumps of carbide begin to blur.

The device can be assembled in another way. The liquid to be dehydrated is placed in a Claisen flask. The neck of the flask, which is connected to the refrigerator, is filled with calcium carbide. The liquid is distilled, and its vapors are dehydrated as they pass through the carbide layer. The dehydrated liquid is collected in a receiver, taking care to ensure that the distilled liquid does not reabsorb water vapor from the environment.

Using CaC2, it is possible not only to dehydrate a liquid, but also to quantify the water content in it; To do this, the acetylene formed is captured with acetone and determined in the form of copper acetylene. The amount of copper acetylene is used to judge the water content in the liquid. This drying method is one of the best. Its disadvantage is that acetylene gets into the dehydrated liquid, which can only be removed by heating.

Another thing worth mentioning is dehydration by freezing; thus, for example; benzene can be dehydrated. The latter turns into a solid state at 4°C. By cooling aqueous benzene to 1 or even 0°C, crystalline benzene is obtained, and the separated water is drained.

The so-called gypsum method * for dehydrating alcohol deserves mention. In addition, the use of magnesium perchlorate (a strong water-removing agent, superior even to phosphorus anhydride) is recommended. The latter substance can be used for drying mainly chemically resistant substances.

If a drying agent is added to liquids with high viscosity, drying continues for a long time and, in addition, a significant amount of liquid remains on the surface of the solid. In these cases, it is recommended to add a suitable dry solvent (for example, ether) to the liquid to be dried and then dry it as described above. During subsequent distillation, the solvent can be easily removed.

In many cases, especially when analyzing organic substances, when determining carbon and hydrogen, anhydrous calcium sulfate (CaSO4) is used as a water absorber. Anhydrous calcium sulfate is obtained by heating dihydrate or hemihydrate calcium sulfate at a temperature of 225±5°C. The temperature at which CaSO4 is dried is very important for obtaining a preparation suitable for the rapid absorption of water vapor. Under no circumstances should heating be allowed above the specified temperature. Before drying, CaSO4 2H2O or CaSO4 0.5H2O is crushed and sifted through a sieve with cells of 1-2 mm. The sifted grains (but not the fines that have passed through the sieve!) are placed in calcium chloride tubes, most often U-shaped, which are heated for 2-3 hours at 225 ± 5 ° C with air previously dried over Pr05 drawn through them. The air flow rate is about 50 ml/min. When CaSO4 reacts with water, the hemihydrate CaSO4 0.5H2O is formed. Anhydrous calcium sulfate can absorb 6.6% of water from the total mass. It can be regenerated many times, it is neutral, chemically inert and does not blur when saturated with water.

* Luhder E., Z. Spirilusinduslrie S., 7, 67 (1934).

Choosing the right drying agent for each case is very important, since if you select the wrong dehydrating agent, you can ruin the whole job. Therefore, it is important to know which drying agents can be used for different substances.

Inorganic substances commonly used for drying can be divided into the following groups:

1. Easily oxidizing metals: Na, Ca.

2. Oxides that easily bind water: CaO, P2O5.

3. Hygroscopic hydroxides: NaOH or KOH.

4. Anhydrous salts: a) alkaline (K2CO3), b) neutral (CaCl2, Na2SO4, CuSO4, CH3COONa).

In table 15 provides instructions for choosing a drying agent when dehydrating various organic liquids.

New methods of dehydration include the use of the principle of water adsorption *. Water is removed from organic solvents by passing them through a glass column with a diameter of 15-40 mm filled with activated Al2O3. According to the completeness of dehydration by this method, solvents are arranged in the following row: benzene > chloroform > diethyl ether > ethyl acetate > acetone. Ethyl alcohol can be dehydrated up to 99.5% with this absorbent.

Together with water, A1203 also sorbs many other contaminants. Spent A1203 is not regenerated and replaced with fresh one.

A very effective way of drying organic liquids and gases is drying with zeolites, the residual moisture is equal to ten thousandths of a percent.

NaA zeolite is suitable for deep drying of transformer oil, various oil fractions, refrigerants, alcohols, as well as many petrochemical synthesis products.

CaA zeolite can be used for selective extraction of polar substances (H2O, H2S1CO2, etc.).

* Angew. Chem., 67, Ki 23, 741 (1955); RZHKhim, 1955, Ki 14, 85, ref. 42799; Lab. Sci., 4, no. 4, 111 (1956); RJHnm. 1957, Ki 8, 95, ref. 26289; Chem. Rund., 11, K." 7, 164 (1958); RZhKhim, 1959, Ka 1, 163, ref. 1120.

Products used for drying organic liquids

Option 5

Alcohols and phenols.

1. For an alcohol of composition C5H12O (I) and (II), the corresponding monochloro derivatives are obtained under the action of PCl5; upon dehydration of the latter, the same alkene 2-methyl-2-butene is obtained. Write the structural formulas of alcohols (I) and (II).

2. For what reason and under what conditions can monohydric alcohols react with each other? What substances are formed?

3. Give an explanation why the first representatives of alcohols are liquid substances.

4. Compose reaction equations in accordance with the diagram. Decipher the unknown substances - give their structural formula and name.

5. To burn 50 ml of methanol (p = 0.80 g/ml), volume of air is required:

a) 150l b) 200l c) 250l d) 180l

6. To completely neutralize a mixture of phenol and acetic acid, 46.8 ml of a 20% by weight KOH solution with a density of 1.2 g/ml is required; when the same mixture reacts with bromine water, 33.1 g of precipitate is formed. Determine the mass fractions of acetic acid and phenol in the initial mixture.

Test 90 min.

Option – 10

1) Make up the structural formulas of isomeric alcohols and ethers corresponding to the formula C3H8O. Name them.

2) To recognize ethanol and glycerol use:

a) Hydrogen chloride

c) Acetic acid

d) Copper(II) hydroxide

Write an equation for the reaction.

3) Write the equation of the chemical reactions that need to be carried out to obtain phenol from calcium carbide and indicate the conditions for their implementation.

4) Write the reaction equations with which you can carry out the following transformations:

Specify reaction conditions.

5) Bromine water was added to 50g of a 2.6% phenol solution until the end of the reaction. Determine what mass of 2% sodium hydroxide solution needs to be added to the reaction mixture to completely neutralize it. Write the reaction equation.

6) What mass of sodium phenolate can be obtained by reacting 4.7 g of phenol with a 4.97 ml sodium hydroxide solution (p = 1.38 g/ml)? The mass fraction of sodium hydroxide in the solution is 35%.

Test for 90 minutes

Option No. 4

1. Write the reaction equations that can be used to convert 1-propanol into 2-propanol.

2. match the formula of the substance and the method of its preparation:

3. Acid properties are most pronounced in:

1) phenol 2) methanol 3) ethanol 4) glycerol

5. When 13.8 g of ethanol was oxidized with copper (II) oxide weighing 28 g, 9.24 g of aldehyde was obtained with a practical yield:

A) 70% B) 75% C) 60% D) 85%

6. Calcium carbide was used to dehydrate ethanol. What is the mass (in grams) of calcium carbide that must be added to 150 ml of calcium alcohol with a density of p = 0.8 g/ml containing 96% ethanol to obtain anhydrous alcohol?

Test 90 min.

Option 12

1. The presence of a functional group in alcohol molecules does not affect:

A) solubility in water B) boiling point

B) structure of the hydrocarbon radical D) characteristic chemical properties

2. What chemical properties does the compound have, the structural formula of which is CH2=CH-CH2OH? Confirm your answer by composing the appropriate reaction equations. Specify the conditions for their holding.

3. Two test tubes contain ethyl alcohol and ethylene glycol. How can you distinguish between these substances?

4. Create reaction equations in accordance with the transformation schemes:

Calcium carbide → acetylene → benzene → chlorobenzene → phenol → trinitrophenol

Specify the reaction conditions.

5. Calculate the mass of ethylene glycol that can be obtained from 200 g of an aqueous solution with a mass fraction of ethanol of 92%.

6. When 9 g of saturated monohydric alcohol was oxidized with copper (II) oxide, 9.6 g of copper was obtained. Determine the molecular formula of alcohol. Calculate the mass of the aldehyde formed if its yield is 90%

LABORATORY WORK No. 1

Experience 1. Production of methane and experiments with it

Equipment and reagents: Round bottom test tube, alcohol lamp, tripod, tripod foot, stopper with gas outlet glass and rubber tube, tube with pulled end, two U-shaped tubes, matches, porcelain mortar and pestle, sodium acetate, bromine solution in water, calcium oxide , sodium hydroxide, potassium permanganate solution, activated carbon, electric stove, glass rod.

Procedure: Sodium acetate is dehydrated before the experiment. Salt CH 3 COONa. 3H 2 O is placed in a porcelain cup and heated, stirring with a glass rod. Sodium acetate first dissolves in the water of crystallization, then, after the water evaporates, it is released in solid form. Once the hardened salt has melted again, it is allowed to cool in a desiccator and crushed in a mortar and pestle.

Calcium oxide is calcined before use, cooled in a desiccator and crushed.

Calcium oxide is added to caustic soda, previously crushed in a porcelain mortar, in a ratio of 2:1 by volume of powders. The resulting mixture is called soda lime. Calcium oxide is necessary to eliminate the hygroscopicity of caustic soda.

A round-bottomed reaction tube is filled 3/4 full with a mixture of sodium acetate and soda lime in a powder volume ratio of 1:3 or 1:2. The mixture is thoroughly mixed in a porcelain mortar. Assemble the device according to Fig. 1.

Rice. 1. Production of methane and experiments with it.

The reaction tube is connected to a system of two U-shaped tubes. The right elbow of the second tube is closed with a stopper with a glass tube having an extended end. The tube is filled with activated carbon. A weak solution of potassium permanganate is poured into one U-shaped tube, and bromine water into the other. The reactor tube is heated. Excessive overheating is avoided, which leads to side reactions and the production of undesirable products - acetone, unsaturated hydrocarbons, carbon dioxide, etc. To capture these substances, use a glass tube with activated carbon, which is connected to the gas outlet tube before the gases enter the first U-shaped handset.

Methane obtained during the reaction passes through solutions of KMnO 4 and Br 2, no discoloration of the solutions is observed (the installation is sealed if gas bubbling occurs synchronously in both solutions). At the end of the experiment, bring the flame of a match or splinter to the hole of the tube with the end pulled out. Methane combustion is observed. Write down the equations of chemical reactions.

Safety precautions: Ignite methane after establishing a stable synchronous bubbling of gas in solutions, but not in the first minutes of methane passage. Follow the heating rules and do not hold the alcohol lamp with your hands.

Disposal. Reuse KMnO 4 solution and bromine water. Transfer the reaction product - sodium carbonate with an admixture of sodium acetate and soda lime - completely into a neutralizer container. Wash U-shaped tubes under a hood with a weak alkaline solution of calcium hydroxide.

Experiment 2. Production of ethylene and experiments with it.

Equipment and reagents: Reaction tube, gas outlet tube, two U-shaped tubes, glass tube with activated carbon (with a pulled end), alcohol lamp, stands with legs, boilers, calcium chloride tube, ethyl alcohol, concentrated sulfuric acid, bromine water, permanganate solution potassium, activated carbon.

Procedure: A pre-prepared and cooled mixture (6 ml) of one part alcohol with three parts concentrated sulfuric acid is poured into a dry test tube-reactor (Fig. 2). Several boilers are placed in the test tube to ensure uniform boiling of the reaction mixture. The test tube is fixed in a stand. Connect the reactor tube to the U-shaped tubes using rubber hoses (see installation figure) containing the KMnO 4 solution and bromine water. The right elbow of the second U-shaped tube is closed with a stopper with an inserted glass tube having an extended end. The tube is filled with pre-activated carbon.

Since in the process of heating alcohol and sulfuric acid, in addition to ethylene, other substances are obtained (SO 2, diethyl ether, CO 2, etc.), some of which can also discolor the KMnO 4 solution and bromine water, then on the way of the gas mixture from the test tube-reactor before the first U-shaped tube, you should

Rice. 2. Production of ethylene and experiments with it.

place a calcium chloride tube with activated carbon.

Heat the reactor tube to a uniform boil. Observe the uniform synchronous bubbling of air and then ethylene through the KMnO 4 solution and bromine water. The color of the solutions gradually disappears. After the solutions have completely discolored, bring the flame of a match or a burning splinter to the tube with the end pulled out and ignite the ethylene. Write reaction equations and explain the observed phenomena.

Safety precautions. Ignite ethylene after complete decolorization of the KMnO 4 solution and bromine water. The device must be sealed, which is determined by the synchronous bubbling of gas through solutions of KMnO 4 and bromine water.

Disposal. Due to the oxidation of alcohol, a charred mixture of uncertain composition remains in the reactor tube, which is completely transferred to a neutralizer container. Add a little strong acidified H 2 SO 4 KMnO 4 solution to the solution remaining after bleaching potassium permanganate and boil it. All existing organic compounds are oxidized to carbon dioxide and water:

C x H y O z + KMnO 4 + H 2 SO 4 → MnSO 4 + K 2 SO 4 + CO 2 + H 2 O.

KMnO 4 solution can be used repeatedly. For utilization of the resulting MnSO 4 (after working off the solution), see: Class VIII, topic “Halogens”. Add a small portion of iron powder and a few drops of medium concentration hydrochloric acid to the solution remaining after bleaching bromine water:

Fe + HCI = FeCI 2 + 2H.

After some time, bromine derivatives will be reduced by atomic hydrogen to hydrocarbons and bromide ions, for example, according to the scheme:

The resulting solution is a yellowish-brown color of bromine water, which can be used to determine unsaturated hydrocarbons and demonstrate the oxidizing properties of bromine. Next, the iron powder is separated by filtration, which is washed, dried and used again.

LABORATORY WORK No. 2

Experiment 1. Production of ethylene by dehydration of ethanol over aluminum oxide

The experience described above in producing ethylene by dehydration of ethanol in the presence of H 2 SO 4 (conc) leads to the formation of large amounts of sulfur oxide (IV) and many other toxic compounds hazardous to the environment. Sulfur (IV) oxide very quickly discolors the KMnO 4 solution and bromine water, which makes the described experiment incorrect for educational demonstration purposes: C 2 H 5 OH + 2H 2 SO 4 = 2C + 2SO 2 + 5H 2 O, then:

C + 2H 2 SO 4 = CO 2 + 2SO 2 + 2H 2 O (when heated)

5SO 2 +2KMnO 4 +2H 2 O = K 2 SO 4 +2MnSO 4 +2H 2 SO 4

SO 2 +Br 2 +2H 2 O = H 2 SO 4 +2HBr

A simpler and more environmentally friendly option for producing ethylene is based on passing alcohol vapor over a heated solid aluminum oxide catalyst.

Equipment and reagents: Demonstration round-bottomed test tube, glass and rubber gas outlet tubes, two U-shaped tubes, test tubes, glass tube with an extended end, tripod, tripod foot, alcohol lamp, splinter, ethanol, washed and calcined sand, clay catalyst mixed with aluminum oxide, distilled water.

Work progress: Prepare the catalyst. To do this, the day before class, mix clay with aluminum oxide in a 2:1 ratio, moisten it with water, mix well and roll out peas, which are air-dried.

Dry sand (3-4 cm high) is poured into the demonstration tube (1) and soaked in alcohol. The catalyst is placed on top of the sand almost to the edge of the test tube. The reactor tube is fixed in the leg of the tripod with a slight slope (the bottom is higher than the hole) and connected to two U-shaped tubes (Fig. 3). The catalyst is thoroughly heated, then the sand soaked in alcohol is heated with another alcohol lamp so that there is always alcohol vapor in the container (do not overheat!). Under these conditions, in addition to ethylene, butadiene can also be produced, which casts doubt on the correctness of the experiment. To absorb butadiene, ethanol is poured into the first U-shaped tube (2). The solubility of butadiene in alcohol is 15 ml per 100 ml of solvent. All butadiene remains in alcohol, since the gas mixture leaving the first U-shaped tube does not give a pink color with a solution of a high-quality reagent for butadiene - quinone.

Rice. 3. Production of ethylene by dehydration of ethanol over a solid catalyst.

Another U-shaped tube (3) is filled with alcohol or water to produce an ethylene solution. The solubility of ethylene in water and alcohol is 25.6 and 360 ml per 100 ml of solvent, respectively. Thus, it is possible to obtain a solution of ethylene in water and alcohol, which is used for the determination of unsaturated organic substances.

The extension of the last U-shaped tube is connected to a gas outlet tube, which is placed in a test tube (4) first with bromine water and then with a solution of potassium permanganate. Discoloration of the solutions is observed. Before the end of the experiment, a glass tube with an extended end is attached to the gas outlet tube. Ethylene is set on fire with a splinter flame. Observe the combustion of ethylene with a luminous flame. Write the reaction equations.

Safety precautions. 1. The demonstration reactor tube is heated evenly to prevent cracking and combustion of gaseous substances formed in the test tube. 2. Place a baking sheet with sand under the heated test tube. 3. The installation must be sealed.

Disposal. A solution of butadiene and ethylene in alcohol should be used in alcohol lamps, as well as to demonstrate their unsaturated nature. Dispose of the decolorized solution of KMnO 4 and bromine water according to the instructions in the previous experiment.

Experience 2. Preparation of acetylene and experiments with it

Equipment and reagents: Wurtz demonstration tube, glass and rubber gas tubes, two U-shaped tubes, a tube with an extended end filled with activated carbon, stands, tripod arms, syringe, syringe needle, rubber stoppers, tweezers, splinter, matches, calcium carbide , saturated sodium chloride solution, KMnO 4 solution, bromine water.

Procedure: Carefully place several pieces of calcium carbide into the Wurtz tube (4). The opening of the test tube is closed with a stopper (5). Next, connect the reactor tube with U-shaped tubes according to Fig. 4.

The work is carried out on a demonstration table, since the by-products of the reaction of technical calcium carbide with water are completely absorbed by the adsorbent - activated carbon. It is important to ensure the tightness of the installation, which is achieved by tightly fitting the plugs and rubber tubes to the glass test tubes and glass tubes.

Rice. 4. Preparation of acetylene and experiments with it.

The right elbow of the second U-shaped tube is closed with a stopper containing a glass tube filled with activated carbon. A diluted solution of KMnO 4 and bromine water is poured into U-shaped tubes. Using a long syringe needle, pierce the rubber hose connecting the reactor to the first U-shaped tube, and slowly introduce a saturated solution of sodium chloride into the reactor tube with calcium carbide, adjusting the amount of added solution and the intensity of acetylene release.

Discoloration of solutions of KMnO 4 and bromine water is observed. After the solutions have decolorized, bring the flame of a splinter to a tube with activated carbon and observe the smoky flame of burning acetylene. Write equations of chemical processes and explain the observed phenomena.

Safety precautions. Do not pick up pieces of calcium carbide with your hands. Add an aqueous solution of sodium chloride to calcium carbide in small portions. Use up all the calcium carbide. Check the tightness of the installation: there should be synchronous bubbling of gas bubbles through both solutions in the U-shaped tubes.

Disposal. Pour a strong KMnO 4 solution from a syringe into the reactor tube and mix the contents. Acetylene and other hydrolysis products (H 2 S, PH 3, etc.) are oxidized, the air remains clean. After some time, open the test tube and pour the resulting suspension of complex composition into a neutralizer container with an alkaline solution.

Disposal of the bleached KMnO 4 solution and bromine water is carried out according to the instructions in experiment No. 2.