Test "Nitrogen and its compounds"

Option 1 1. Strongest Molecule: a) H 2; b) F 2; c) O 2; d) N 2. 2. Coloring of phenolphthalein in ammonia solution: a) crimson; b) green; c) yellow; d) blue. 3. The oxidation state is +3 at the nitrogen atom in the compound: a) NH 4 NO 3; b) NaNO 3; c) NO 2; d) KNO 2. 4. Thermal decomposition of copper (II) nitrate produces:a) copper (II) nitrite and O 2 ; b) nitric oxide (IV) and О 2 ; c) copper (II) oxide, brown gas NO 2 and O 2; d) copper (II) hydroxide, N 2 and O 2. 5. What ion is formed by the donor-acceptor mechanism? a) NH 4 +; b) NO 3 -; c) Cl -; d) SO 4 2–. 6. Indicate strong electrolytes: a) nitric acid; b) nitrous acid; c) an aqueous solution of ammonia; d) ammonium nitrate. 7. Hydrogen is released during the interaction: a) Zn + HNO 3 (dil.); b) Cu + HCl (solution); c) Al + NaOH + H 2 O; d) Zn + H 2 SO 4 (dil.); e) Fe + HNO 3 (conc.). 8. Write the equation for the reaction of zinc with very dilute nitric acid if one of the reaction products is ammonium nitrate. Indicate the coefficient in front of the oxidizing agent. 9.

Give names to substances A, B, C. Option 2 1. By displacing water it is impossible to collect: a) nitrogen; b) hydrogen; c) oxygen; d) ammonia. 2. The reagent for the ammonium ion is a solution of: a) potassium sulfate; b) silver nitrate; c) sodium hydroxide; d) barium chloride. 3. With the interaction of НNО 3 (conc.) gas is formed with copper shavings: a) N 2 O; b) NH 3; c) NO 2; d) H 2. 4. Thermal decomposition of sodium nitrate forms: a) sodium oxide, brown gas NO 2, O 2; b) sodium nitrite and O 2; c) sodium, brown gas NO 2, O 2; d) sodium hydroxide, N 2, O 2. 5. Oxidation degree of nitrogen in ammonium sulfate: a) –3; b) –1; c) +1; d) +3. 6. Which of these substances does concentrated HNO react with? 3 under normal conditions? a) NaOH; b) AgCl; c) Al; d) Fe; e) Cu. 7. Specify the number of ions in the abbreviated ionic equation for the interaction of sodium sulfate and silver nitrate: a) 1; b) 2; at 3; d) 4. 8. Write the equation for the interaction of magnesium with dilute nitric acid if one of the reaction products is a simple substance. Indicate the coefficient in front of the oxidizer in the equation. 9. Write the reaction equations for the following transformations:

Give names to substances A, B, C, D.

Answers

Option 1 1 - G; 2 - a; 3 - G; 4 - v; 5 - a; 6 - a, d; 7 - c, d; 8 – 10,

9.A - NH 3, B - NH 4 NO 3, C - NO,

Option 2 1 - d; 2 - c; 3 - c; 4 - b; 5 - a; 6 - a, d; 7 - c,

2Ag + + SO 4 2– = Ag 2 SO 4;

8 – 12, 9.A - NO, B - NO 2, C - HNO 3, D - NH 4 NO 3,

PRACTICAL WORK (1 h) 8 CLASS

The work is carried out by students independently under the supervision of a teacher.
I propose the result of my many years of work on the preparation and conduct of practical work in a secondary school in chemistry lessons in grades 8-9:

• "Obtaining and properties of oxygen",
• "Preparation of solutions of salts with a certain mass fraction of a solute",
• "Generalization of information about the most important classes of inorganic compounds",
• "Electrolytic dissociation"
• "Oxygen subgroup" (see the next issue of the newspaper "Chemistry").

All of them have been tested by me in the classroom. They can be used in the study of the school chemistry course both according to the new program of O.S. Gabrielyan, and according to the program of G.E. Rudzitis, F.G. Feldman.
A student experiment is a kind of independent work. The experiment not only enriches students with new concepts, abilities, skills, but is also a way to test the truth of the knowledge they have acquired, contributes to a deeper understanding of the material, the assimilation of knowledge. It allows you to more fully implement the principle of variability of perception of the surrounding world, since the main essence of this principle is the connection with life, with the future practical activities of students.

Goals... To be able to obtain oxygen in the laboratory and collect it by two methods: displacement of air and displacement of water; to confirm empirically the properties of oxygen; know the safety rules.
Equipment... A metal stand with a foot, an alcohol lamp, matches, a test tube with a gas outlet tube, a test tube, a cotton ball, a pipette, a beaker, a splinter, a dissecting needle (or wire), a crystallizer with water, two conical flasks with stoppers.
Reagents... KMnO 4 crystalline (5-6 g), lime water Ca (OH) 2, charcoal,
Fe (steel wire or paper clip).

Safety rules.
Handle chemical equipment with care!
Remember! The test tube is warmed up, holding it in an inclined position, along its entire length, with two or three movements in the flame of an alcohol lamp. When heating, direct the opening of the tube away from yourself and your neighbors.

Previously, students receive homework related to the study of the content of the upcoming work according to the instructions, at the same time using materials from the 8th grade textbooks by O.S. Gabrielyan (§ 14, 40) or G.E. Rudzitis, F.G. Feldman (§ 19 , twenty). In notebooks for practical work, they write down the name of the topic, the purpose, list the equipment and reagents, draw up a table for the report.

DURING THE CLASSES

I put one experience higher
than a thousand opinions
born only
imagination.

M.V. Lomonosov

Oxygen production
air displacement

(10 min)

1. Place potassium permanganate (KMnO 4) into a dry test tube. Place a loose cotton ball at the opening of the test tube.
2. Close the test tube with a stopper with a gas outlet tube, check for leaks (Fig. 1).

Rice. one. Checking the device for tightness

(Explanations of the teacher on how to test the device for leaks.) Mount the device in the tripod leg.

3. Lower the gas outlet tube into the glass, without touching the bottom, at a distance of 2-3 mm (Fig. 2).

4. Heat the substance in the test tube. (Remember the safety rules.)
5. Check for gas with a smoldering speck (coal). What are you watching? Why can oxygen be collected by air displacement?
6. Collect the resulting oxygen in two flasks for the following experiments. Cap the flasks.
7. Prepare the report using the table. 1, which you place on the spread of your notebook.

Oxygen production
water displacement

(10 min)

1. Fill the tube with water. Close the tube with your thumb and turn it upside down. In this position, lower your hand with the test tube into the crystallizer with water. Bring the test tube to the end of the gas outlet tube without removing it from the water (Fig. 3).

2. When oxygen has displaced water from the tube, close it with your thumb and remove it from the water. Why can oxygen be collected by displacing water?
Attention! Remove the gas outlet tube from the crystallizer, without stopping heating the tube with KMnO 4. If this is not done, then the water will be transferred to a hot test tube. Why?

Combustion of coal in oxygen

(5 minutes)

1. Attach the ember to a metal wire (dissecting needle) and bring it into the flame of an alcohol lamp.
2. Dip a red-hot coal into a flask with oxygen. What are you watching? Give an explanation (fig. 4).

3. After removing unburned coal from the flask, pour 5-6 drops of lime water into it
Ca (OH) 2. What are you watching? Give an explanation.
4. Fill out a report on the work in table. one.

Burning steel (iron) wire
in oxygen

(5 minutes)

1. Attach a piece of a match to one end of the steel wire. Light a match. Dip the wire with a burning match into a flask with oxygen. What are you watching? Give an explanation (fig. 5).

2. Fill out a report on the work in table. one.

Table 1

Operations performed (what they were doing)	Figures with the designation of the starting and obtained substances	Observations. Conditions carrying out reactions. Reaction equations	Explanations of observations. conclusions
Assembling the device for obtaining oxygen. Checking the device for leaks
Oxygen production from KMnO 4 when heated
Proof of oxygen production with smoldering splinter
Characteristics of the physical properties of O 2. Collection of O 2 by two methods: air displacement, water displacement
Characteristic chemical properties of O 2. Interaction with simple substances: burning coal, burning iron (steel wire, paper clip)

Make a written summary of the work done (5 min).

CONCLUSION... One of the ways to obtain oxygen in the laboratory is to decompose KMnO 4. Oxygen is a colorless and odorless gas, 1.103 times heavier than air ( M r(O 2) = 32, M r(air) = 29, from which it follows 32/29 1.103), slightly soluble in water. Reacts with simple substances to form oxides.

Tidy up the workplace (3 minutes): disassemble the appliance, arrange the dishes and accessories in their places.

Submit your notebooks for review.

Homework.

Task... Determine which of the iron compounds - Fe 2 O 3 or Fe 3 O 4 - is richer in iron?

Given:	Find:
Fe 2 O 3, Fe 3 O 4.	(Fe) in Fe 2 O 3, "(Fe) in Fe 3 O 4

Solution

(X) = n A r(X) / M r, where n- the number of atoms of element X in the formula of a substance.

M r(Fe 2 O 3) = 56 2 + 16 3 = 160,

(Fe) = 56 2/160 = 0.7,
(Fe) = 70%,

M r(Fe 3 O 4) = 56 3 + 16 4 = 232,
"(Fe) = 56 3/232 = 0.724,
"(Fe) = 72.4%.

Answer... Fe 3 O 4 is richer in iron than Fe 2 O 3.

The teacher, during practical work, observes the correctness of the implementation of techniques and operations by students and notes in the card of the account of skills (Table 2).

table 2

Skill record card

Practical work operations	Surnames of students
	A	B	V	G	D	E
Oxygen production device assembly
Checking the device for leaks
Strengthening the tube in the tripod leg
Handling an alcohol lamp
Heating a test tube with KMnO 4
O 2 emission check
Collecting O 2 into a vessel by two methods: air displacement, water displacement
Burning coal
Combustion Fe (steel wire)
Experiment culture
Registration of work in a notebook

Sample report on the done practical work (table. 1)

О 2 is obtained in the laboratory by decomposition of KMnO 4 by heating Proof of oxygen production with
smoldering splinter Smoldering splinter
(coal) lights up brightly
in O 2 The resulting O 2 gas supports combustion Characteristic
physical properties of О 2. Collection of O 2 by two methods:
air displacement (a),
water displacement (b)

Oxygen displaces air and water from vessels Oxygen is a colorless and odorless gas,
slightly heavier than air, therefore
it is collected in a vessel placed on the bottom. Oxygen is slightly soluble in water Characterization of the chemical properties of O 2. Interaction with simple substances: coal combustion (a), iron combustion (steel wire, paper clip, shavings) (b)

A red-hot ember burns brightly in O 2:

Lime water becomes cloudy, because a water-insoluble precipitate CaCO 3 is formed:
CO 2 + Ca (OH) 2 CaCO 3 + H 2 O. Iron burns with a bright flame in oxygen:

O 2 interacts
with simple
substances - metals and non-metals. The formation of a white precipitate confirms the presence of CO 2 in the flask.

Gaseous substances from the course of inorganic and organic chemistry

In preparation for the upcoming exams, graduates of the 9th and 11th grades need to study the issue of gaseous substances (physical properties, methods and methods of production, their recognition and application). Having studied the topics of the specification of the OGE and USE exams (on the websitewww. fipi. ru ), we can say that there is practically no separate question on gaseous substances (see table):

Unified State Exam

№14 (Typical chemical properties of hydrocarbons: alkanes, cycloalkanes, alkenes, dienes, alkynes, aromatic hydrocarbons (benzene and toluene). The main methods of obtaining hydrocarbons (in the laboratory);№26 (Rules for working in a laboratory. Laboratory glassware and equipment. Safety rules for working with caustic, flammable and toxic substances, household chemicals. Scientific methods for the study of chemicals and transformations. Methods for separating mixtures and purifying substances. Concept of metallurgy: general methods of obtaining metals General scientific principles of chemical production (on the example of industrial production of ammonia, sulfuric acid, methanol) Chemical pollution of the environment and its consequences Natural sources of hydrocarbons, their processing High molecular weight compounds Polymerization and polycondensation reactions Polymers Plastics, fibers, rubbers)

So, in option number 3 (Chemistry. Preparation for the OGE-2017. 30 training materials for the demo version of 2017. 9th grade: teaching aid / edited by V.N. Doronkin. - Rostov n / a: Legion, 2016. - 288 p.) Students are asked to answer the following question (No. 13):

Are the following judgments about the methods of obtaining substances correct?

A. Ammonia cannot be collected by displacing water.

B. Oxygen cannot be collected by displacing water.

1) only A is true

2) only B is true

3) both statements are true

4) both judgments are wrong

To answer the question, the guys should know the physical and chemical properties of ammonia and oxygen. Ammonia interacts very well with water; therefore, it cannot be obtained by displacing water. Oxygen dissolves in water, but does not interact with it. Therefore, it can be obtained by displacing water.

In option number 4 (Chemistry. Preparation for the exam-2017. 30 training options for the demo version for 2017: study guide / edited by V.N. Doronkin. - Rostov n / a: Legion, 2016. - 544 p. ) students were asked to answer the following question (No. 14):

From the proposed list, select two substances that are formed when a mixture of solid potassium acetate and potassium hydroxide is heated:

1) hydrogen;

2) methane;

3) ethane;

4) carbon dioxide;

5) potassium carbonate

Answer: 2 (decarboxylation reaction)

Moreover, in order to pass the exam, children need to know what is the raw material for obtaining a particular gaseous substance. For example, in the same book edited by Doronkin, question # 26 (option 8) reads like this:

Establish a correspondence between the substance obtained in the industry and the raw materials used to obtain it: for each position marked with a letter, select the corresponding position marked with a number:

Write down the selected numbers in the table under the corresponding letters:

Answer:

In option number 12, students are asked to recall the field of application of some gaseous substances:

Establish a correspondence between the substance and its area of ​​application: for each position indicated by a letter, select the corresponding position indicated by a number:

Answer:

With the children taking the chemistry exam in the 9th grade, in the preparation for the exam, we fill in the following table (in the 11th grade we repeat and expand it):

Hydrogen

The lightest gas, 14.5 times lighter than air, with air in the ratio of two volumes of hydrogen to one volume of oxygen forms "detonating gas"

1. By interaction of alkali and alkaline earth metals with water:

2 Na + 2 H 2 O = 2 NaOH + H 2

2. Interaction of metals (up to hydrogen) with hydrochloric acid (any concentration) and dilute sulfuric acid:

Zn + 2 HCl = ZnCl 2 + H 2

3. Interaction of transition (amphoteric) metals with a concentrated alkali solution when heated:

2Al + 2NaOH ( end ) + 6H 2 O = 2Na + 3H 2

4. Decomposition of water by electric current:

2H 2 O = 2H 2 + O 2

By the characteristic sound of an explosion: a vessel with hydrogen is brought to the flame (a dull clap - pure hydrogen, a "barking" sound - hydrogen with an admixture of air):

2H 2 + O 2 2H 2 O

Hydrogen burner, production of margarine, rocket fuel, production of various substances (ammonia, metals such as tungsten, hydrochloric acid, organic substances)

Oxygen

Colorless gas, odorless; in the liquid state it has a light blue color, in the solid state it is blue; soluble in water better than nitrogen and hydrogen

1. By decomposition of potassium permanganate:

2 KMnO 4 = K 2 MnO 4 + MnO 2 + O 2

2. By decomposition of hydrogen peroxide:

2 H 2 O 2 2 H 2 + O 2

3. Decomposition of berthollet's salt (potassium chlorate):

2KClO 3 = 2KCl + 3O 2

4. Decomposition of nitrates

5. Decomposition of water under the influence of electric current:

2 H 2 O = 2 H 2 + O 2

6. The process of photosynthesis:

6 CO 2 + 6 H 2 O = C 6 H 12 O 6 + 6O 2

Flashing of a smoldering splinter in a container with oxygen

In metallurgy, as an oxidizer for rocket fuel, in aviation for breathing, in medicine for breathing, in blasting operations, for gas cutting and welding of metals

Carbon dioxide

Colorless gas, odorless, 1.5 times heavier than air. Under normal conditions, one volume of carbon dioxide dissolves in one volume of water. At a pressure of 60 atm, it turns into a colorless liquid. When liquid carbon dioxide evaporates, part of it turns into a solid snow-like mass, which is pressed in industry - "dry ice" is obtained.

1. In the industry by calcining limestone:

CaCO 3 CaO + CO 2

2. The action of hydrochloric acid on chalk or marble:

CaCO 3 + 2HCl = CaCl 2 + H 2 O + CO 2

With the help of a burning splinter that goes out in an atmosphere of carbon dioxide, or by the cloudiness of lime water:

CO 2 + Ca(OH) 2 = CaCO 3 ↓ + H 2 O

For creating "smoke" on stage, storing ice cream, in fizzy drinks, in foam fire extinguishers

Ammonia

A colorless gas with a pungent odor, almost 2 times lighter than air. Do not inhale for a long time, because it is poisonous. Easily liquefies at normal pressure and temperature -33.4 O C. When liquid ammonia evaporates from the environment, a lot of heat is absorbed; therefore, ammonia is used in refrigeration units. Let's well dissolve in water: at 20 o C about 710 volumes of ammonia are dissolved in 1 volume of water.

1. In industry: at high temperatures, pressures and in the presence of a catalyst, nitrogen reacts with hydrogen, forming ammonia:

N 2 +3 H 2 2 NH 3 + Q

2. In the laboratory, ammonia is obtained by the action of slaked lime on ammonium salts (most often ammonium chloride):

Ca (OH) 2 + 2NH 4 Cl CaCl 2 + 2NH 3 + 2H 2 O

1) by smell;

2) on a change in the color of wet phenolphthalein paper (became crimson);

3) by the appearance of smoke when bringing a glass rod moistened with hydrochloric acid

1) in refrigeration units; 2) production of mineral fertilizers;

3) production of nitric acid;

4) for soldering; 5) obtaining explosives; 6) in medicine and in everyday life (ammonia)

Ethylene

Under normal conditions, it is a colorless gas with a faint odor, partially soluble in water and ethanol. Let's well dissolve in diethyl ether and hydrocarbons. It is a phytohormone. Possesses narcotic properties. The most produced organic matter in the world.

1) In industry by dehydrogenation of ethane:

CH 3 -CH 3 CH 2 = CH 2 + H 2

2) In the laboratory, ethylene is obtained in two ways:

a) depolymerization of polyethylene:

(-CH 2 -CH 2 -) n nCH 2 = CH 2

b) catalytic dehydration of ethyl alcohol (white clay or pure aluminum oxide and concentrated sulfuric acid are used as a catalyst):

C 2 H 5 OHCH 2 = CH 2 + H 2 O

Oxygen

+

Downside down

+

Upside down

Carbon dioxide

+

Downside down

-

Ammonia

+

Upside down

-

Ethylene

+

Upside down and oblique

-

Thus, in order to successfully pass the OGE and the Unified State Exam, students need to know the ways and methods of obtaining gaseous substances. The most common of these are oxygen, hydrogen, carbon dioxide, and ammonia. In the 11th grade textbook, the children are offered practical work No. 1, which is called “Receiving, collecting and recognizing gases”. It offers five options - obtaining five different gaseous substances: hydrogen, oxygen, carbon dioxide, ammonia and ethylene. Of course, in a lesson lasting 45 minutes, it is simply unrealistic to complete all 5 options. Therefore, before starting this work, students at home fill out the above table. Thus, the children at home, when filling out the table, repeat the methods and methods of obtaining gaseous substances (chemistry course of grades 8, 9 and 10) and come to the lesson already theoretically knowledgeable. Graduates receive two marks for one topic. The work is big in terms of volume, but the guys are happy to do it. And the incentive is - a good mark in the certificate.

Collection of gases

Methods for collecting gases are determined by their properties: solubility and interaction with water, air, gas toxicity. There are two main ways of collecting gas: air displacement and water displacement. Air displacement collect gases that do not interact with air.

Based on the relative density of the gas in the air, a conclusion is made on how to position the vessel for collecting the gas (Fig. 3, a and b).

In fig. 3, a shows the collection of gas with an air density of more than unity, for example, nitrogen oxide (IV), the air density of which is 1.58. In fig. 3, b shows the collection of gas with an air density of less than unity, for example, hydrogen, ammonia, etc.

By displacing water, gases are collected that do not interact with water and dissolve poorly in it. This method is called collecting gas above water , which is carried out as follows (Fig. 3, c). The cylinder or jar is filled with water and covered with a glass plate so that no air bubbles remain in the cylinder. The plate is held by hand, the cylinder is turned over and lowered into a glass bath of water. Under water, the plate is removed, a gas outlet tube is brought into the open hole of the cylinder. The gas gradually displaces water from the cylinder and fills it, after which the opening of the cylinder under water is closed with a glass plate and the cylinder filled with gas is removed. If the gas is heavier than air, then the cylinder is placed upside down on the table, and if it is lighter, then upside down on the plate. Gases above water can be collected in test tubes, which, like the cylinder, are filled with water, closed with a finger and dropped into a glass or glass bath with water.

Poisonous gases are usually collected by displacement of water, since it is easy to note the moment when the gas completely fills the vessel. If there is a need to collect gas by displacing air, then proceed as follows (Fig. 3, d).

A stopper with two gas outlet tubes is inserted into the flask (jar or cylinder). Through one, which reaches almost to the bottom, gas is admitted, the end of the other is lowered into a glass (jar) with a solution that absorbs gas. So, for example, to absorb sulfur (IV) oxide, an alkali solution is poured into a glass, and to absorb hydrogen chloride - water. After filling the flask (jar) with gas, remove the stopper with gas tubes from it and quickly close the vessel with a stopper or glass plate, and place the stopper with gas tubes in a getter solution.

Experience 1. Receiving and collecting oxygen

Assemble the installation according to fig. 4. Place 3-4 g of potassium permanganate in a large dry test tube, close the stopper with a gas outlet tube. Support the tube in a rack with the hole slightly upward. Place a crystallizer with water next to the stand on which the test tube is fixed. Fill an empty test tube with water, cover the opening with a glass plate and quickly turn it upside down into the crystallizer. Then, in water, take out the glass plate. There should be no air in the test tube. Heat potassium permanganate in a burner flame. Immerse the end of the flue gas tube in water. Observe the appearance of gas bubbles.

A few seconds after the beginning of the bubbling, place the end of the gas outlet tube into the opening of the tube filled with water. Oxygen displaces water from the tube. After filling the tube with oxygen, cover the opening with a glass plate and invert.

Rice. 4. A device for obtaining oxygen In a test tube with oxygen, lower the smoldering

1. What laboratory methods of obtaining oxygen do you know? Write down the corresponding reaction equations.

2. Describe the observations. Explain the location of the test tube during the experiment.

3. Write the equation of the chemical reaction for the decomposition of potassium permanganate when heated.

4. Why does a smoldering splinter flash in a test tube with oxygen?

Experience 2. Hydrogen production - the action of a metal on an acid

Assemble the instrument, consisting of a test tube with a stopper, through which a glass tube with a drawn-out end passes (Fig. 5). Place a few pieces of zinc in a test tube and add a dilute sulfuric acid solution. Insert the stopper tightly with the tubing pulled out, fix the tube vertically in the tripod clamp. Observe gas evolution.

Rice. 5. Device for producing hydrogen Hydrogen escaping through the tube must be free of air impurities. Put a test tube turned upside down on the gas outlet tube, after half a minute remove it and, without turning it over, bring it to the burner flame. If pure hydrogen enters the test tube, it ignites quietly (a faint sound is heard during ignition).

If there is an air impurity in a test tube with hydrogen, a small explosion occurs, accompanied by a sharp sound. In this case, the gas purity test should be repeated. After making sure that pure hydrogen is coming out of the device, ignite it at the hole of the drawn tube.

Control questions and tasks:

1. Specify the methods of obtaining and collecting hydrogen in the laboratory. Write down the corresponding reaction equations.

2. Make the equation of the chemical reaction of obtaining hydrogen under the conditions of the experiment.

3. Hold a dry test tube over a hydrogen flame. What substance is formed as a result of the combustion of hydrogen? Write the equation for the reaction of burning hydrogen.

4. How to check the purity of hydrogen obtained during the experiment?

Experience 3. Ammonia production

Rice. 6. Device for obtaining ammonia Place a mixture of ammonium chloride and calcium hydroxide, previously ground in a mortar, into a test tube with a gas outlet tube (Fig. 6). Note the smell of the mixture. Fix the test tube with the mixture in a tripod so that the bottom of it is slightly higher than the hole. Close the tube with a stopper with a gas outlet tube, on the bent end of which put the tube upside down. Heat the mixture vial slightly. Bring a litmus paper moistened with water to the opening of an inverted test tube. Note the color change of the litmus test.

Control questions and tasks:

1. What hydrogen nitrogen compounds do you know? Write their formulas and names.

2. Describe what is happening. Explain the location of the test tube during the experiment.

3. Make the equation of the reaction between ammonium chloride and calcium hydroxide.

Experience 4. Obtaining nitric oxide (IV)

Assemble the device according to fig. 7. Put some copper shavings into a flask, pour 5-10 ml of concentrated nitric acid into a funnel. Pour the acid into the flask in small portions. Collect the evolved gas in a test tube.

Rice. 7. Device for producing nitrogen oxide (IV)

Control questions and tasks:

1. Describe what is happening. What is the color of the gas emitted?

2. Make the equation for the reaction between copper and concentrated nitric acid.

3. What properties does nitric acid have? What factors determine the composition of the substances to which it is reduced? Give examples of reactions between metals and nitric acid, as a result of which the reduction products of HNO 3 are NO 2, NO, N 2 O, NH 3.

Experience 5. Obtaining hydrogen chloride

Place 15-20 g of sodium chloride in a Wurtz flask; into the dropping funnel - a concentrated solution of sulfuric acid (Fig. 8). Insert the end of the gas outlet tube into a dry container for collecting hydrogen chloride so that the tube reaches almost to the bottom. Close the opening of the vessel with a loose cotton ball.

Place a crystallizer with water next to the device. Pour the sulfuric acid solution from the dropping funnel.

Heat the flask slightly to speed up the reaction. When over

with cotton wool, which closes the opening of the vessel, fog will appear,

Rice. 8. Device for obtaining hydrogen chloride stop heating the flask, and lower the end of the gas outlet tube into the flask with water (keep the tube close above the water, without immersing it in water). After taking out the cotton wool, immediately close the opening of the vessel with hydrogen chloride with a glass plate. Turning the vessel upside down, immerse it in a crystallizer with water and remove the plate.

Control questions and tasks:

1. Explain the observed phenomena. What is the reason for the formation of fog?

2. What is the solubility of hydrogen chloride in water?

3. Test the resulting solution with litmus test. What is the pH value?

4. Write the equation for the chemical reaction of the interaction of solid sodium chloride with concentrated sulfuric acid.

Experience 6. Receiving and collecting carbon monoxide (IV)

The installation consists of a Kipp apparatus 1 charged with pieces of marble and hydrochloric acid, two Tishchenko flasks connected in series 2 and 3 (bottle 2 filled with water to clean the passing carbon monoxide (IV) from hydrogen chloride and mechanical impurities, flask 3 - sulfuric acid for gas drying) and flasks 4 with a capacity of 250 ml to collect carbon monoxide (IV) (Fig. 9).

Rice. 9. Device for obtaining carbon monoxide (IV)

Control questions and tasks:

1. Dip the lighted torch into a flask with carbon monoxide (IV) and explain why the flame goes out.

2. Make the equation of the reaction of formation of carbon monoxide (IV).

3. Can a concentrated sulfuric acid solution be used to obtain carbon monoxide (IV)?

4. Pass the gas released from the Kipp apparatus into a test tube with water tinted with a neutral litmus solution. What is being observed? Write down the equations for the reaction that occurs when a gas is dissolved in water.

Control questions:

1. List the main characteristics of the gaseous state of matter.

2. Suggest a classification of gases according to 4-5 essential criteria.

3. How is Avogadro's law read? What is its mathematical expression?

4. Explain the physical meaning of the average molar mass of the mixture.

5. Calculate the average molar mass of the reference air, in which the mass fraction of oxygen is 23%, and nitrogen - 77%.

6. Which of the following gases is lighter than air: carbon monoxide (II), carbon monoxide (IV), fluorine, neon, acetylene C 2 H 2, phosphine PH 3?

7. Determine the hydrogen density of a gas mixture consisting of 56 l argon and 28 l nitrogen. Gas volumes are normalized.

8. An open vessel is heated at a constant pressure from 17 ° C to 307 ° C. What part of the air (by mass) in the vessel is displaced?

9. Determine the mass of 3 liters of nitrogen at 15 ° C and a pressure of 90 kPa.

10. Mass of 982.2 ml of gas at 100 ° C and pressure of 986 Pa is equal to 10 g. Determine the molar mass of the gas.

Analysis of the distribution of physical forces
when using chemical devices

The demonstration experiment and many practical works are based on the use of simple chemical devices. In addition to getting acquainted with the chemical transformations of substances, students should understand the physical essence of what is happening, and be able to explain the essence of what is happening by the drawing of the device: what is going where and what is happening where.

One of the instruments in the chemistry room is a gas meter. In fig. 1 shows a gas meter filled with gas. It can be oxygen, as shown in the figure, carbon dioxide, or just air. Cranes 1 and 2 at this moment are closed. Gas, in accordance with Pascal's law, exerts pressure on the walls of the vessel and on the water. Opening the tap 1 , the column of water from the funnel puts pressure on the gas, pressing it, but since internal gas pressure and water pressure are balanced, nothing happens. Opening the tap 2 , the gas rushes into the outlet (the flow rate is regulated by a careful turning of the valve). The pressure inside the vessel drops - and water from the funnel enters the gasometer. After closing the tap 2 gas extraction stops, the water level is set at a higher mark, because there is a new balance of power. The tap is closed to stop the water pressure. 1 .

The second device, similar to a gas meter, is the Kipp apparatus (Fig. 2). This device can produce hydrogen from zinc and hydrochloric acid (see Fig. 2), hydrogen sulfide from iron sulfide, carbon dioxide from marble. In position a the device is in working order, the tap is open. A strong solution of hydrochloric acid rushes to the bottom of the device, fills it and wets the metallic zinc lying on the copper grid. Zinc dissolves in acid, reacts with it, the resulting hydrogen rushes into the middle sphere of the device, displaces the air, mixing with it. Therefore, the escaping gas must be checked for cleanliness. The distribution of physical forces in the device is shown in Fig. 2 using the arrows.

We close the tap. Hydrogen continues to form, and its amount increases. Since the gas outlet is blocked, pressure increases inside the sphere. It squeezes the acid out of the middle sphere until the acid stops coating the zinc surface. The chemical reaction stops (zinc wetted with acid continues to react with it for some time). The internal pressure in the device, generated by hydrogen, and the pressure created by the hydraulic seal, are balanced.

Consider methods for collecting gases. In fig. 3 shows how to collect gas using the air displacement method. If the gas is toxic, this operation is carried out in a fume hood. Gases that are heavier than air - CO 2, O 2, HCl, SO 2, entering a jar or beaker, displace the air.

In the study of carbon dioxide: its physical properties and inability to support the combustion of organic substances - an entertaining experience of extinguishing a paraffin candle burning in air is demonstrated (Fig. 4). Carbon dioxide, as a heavier gas, goes down under the force of gravity. It fills the container and displaces the air it contains. The candle goes out in an atmosphere of carbon dioxide.

The device shown in Fig. 5, students collect on practical work "Obtaining oxygen and studying its properties." This device illustrates the method of collecting gas by air displacement (the physical basis for relative density).

Another method of collecting gases is associated with the displacement of water from the vessel. In this way, it is possible to collect gases that are slightly soluble in water, in particular nitric oxide (II) (Fig. 6). Reactor gas 1 enters the gas outlet pipe 2 placed under the upside-down cylinder 3 ... Passing through the water column, the gas collects in the area of ​​the cylinder bottom. Under gas pressure, water is pushed out of the cylinder.

If the gas is poorly soluble in water, then this gas can

but saturate the water as shown in fig. 7. In such a device, you can get chlorine (see Fig. 7) or sulfur dioxide by adding concentrated sulfuric acid to sodium sulfite crystals. The gas obtained in the Würz flask enters the gas outlet tube, which is immersed in water at the end. The gas partially dissolves in water, partially fills the space above the water, displacing the air.

If the gas is highly soluble in water, then it cannot be collected by water displacement. In fig. Figures 8 and 9 show how the hydrogen chloride and ammonia are collected by the air displacement method. The same fig. 8 and 9
(see p. 22) shows the dissolution of gases when immersed tubes with HCl and NH 3 hole in water.

If you saturate with hydrogen chloride from a test tube (with reagents) with a gas outlet tube dipped in water (Fig. 10), then the first portions of gas instantly dissolve in water. About 500 liters of hydrogen chloride is dissolved in 1 liter of water, therefore, the incoming gas does not create excessive pressure. In fig. 10 a consistent change in gas pressure is noted p internally in a reaction tube in relation to atmospheric pressure p atm. The pressure inside the device becomes less than the external pressure, and water rapidly fills the gas outlet pipe and the device itself. In addition to spoiling the experiment, the test tube may crack.

When studying the chemical properties of metallic sodium (Fig. 11), it is important not only to observe its behavior in reaction with water, but also to explain the observed phenomena. The first observation is that sodium remains on the surface of the water, therefore, its density is less than one (the density of water). The second observation is that sodium "rushes" through the water due to the repulsive effect of the released gas. The third observation is that sodium melts and turns into a ball. Sodium react with water is exothermic. The released heat is enough to melt sodium, therefore, it is a low-melting metal. The fourth observation is that the reaction is accompanied by outbreaks; therefore, the heat of reaction is sufficient both for the spontaneous combustion of sodium and for the microexplosion of hydrogen. If the reaction is carried out in a narrow space (in a test tube), and even with a large piece of sodium, then the explosion of hydrogen cannot be avoided. To avoid an explosion, the reaction is carried out in a crystallizer or in a large-diameter beaker and using a small piece of sodium.

It is necessary to pay great attention to the rule of dissolving concentrated sulfuric acid in water (Fig. 12). The acid, as a heavier liquid, rushes to the bottom of the round-bottomed flask. Everything else is shown in fig. 12.

The formation of physicochemical thinking is facilitated by the study of oxygen (both in the initial course of chemistry and in the course of organic chemistry). We are talking about the use of oxygen and acetylene in welding and autogenous metal cutting (Fig. 13). When welding, a high-temperature flame of acetylene burning in oxygen (up to 2500 ° C) is directed to the metal wire and the place to be welded. The metal melts, you get a seam. In autogenous cutting, the flame melts the metal, and the excess oxygen burns it out.

Not every chemistry classroom contains silicon as a simple substance. Let's check it for electrical conductivity using a simple device: a probe with elastic elongated iron ends, a light bulb (mounted on a stand), and an electric wire with a plug (Fig. 14). The lamp glows, but not brightly - it is clear that silicon conducts an electric current, but provides significant resistance to it.

The chemical element silicon is an analogue of carbon, but the radius of its atoms is greater than the radius of carbon atoms. Silicon, as a simple substance, has the same (as diamond) crystal lattice (atomic) with a tetrahedral orientation of chemical bonds. In a diamond, covalent bonds are strong; it does not conduct an electric current. In silicon, as even a rough experiment shows, some part of the electron pairs is vaporized, which causes some electrical conductivity of the substance. In addition, silicon heats up (some students have the opportunity to verify this), which also indicates the resistance of the substance to electric current.

Students observe with great interest the study of the physical and chemical properties of benzene (Fig. 15). Add a layer of benzene ~ 2 mm thick to a small amount of water (see Fig. 15, a). It can be seen that the two colorless liquids do not mix. Mix this stratified mixture with vigorous shaking, we get a "gray" emulsion. We fix the tube in an upright position. Students observe a gradual separation of benzene and water, and at first the lower level of the content becomes transparent, and after a short time we obtain the initial distribution. Water molecules are lighter than benzene molecules, but their density is somewhat higher. The interaction between non-polar benzene molecules and polar water molecules is insignificant, very weak, so most of the benzene is pushed out to the water surface (see Fig. 15, b).

Now add benzene to a few milliliters of bromine water (low color intensity) (see Fig. 15, b). The fluids are immiscible. Mix vigorously the contents of the test tube and let the system settle. Bromine, previously dissolved in water, is extracted into the benzene layer, which is evident from the color change and an increase in its intensity.

Add a few milliliters of a weak alkali solution to the contents of the test tube.
(see fig. 15, b). Bromine reacts with alkali. The benzene layer is discolored, and the formed inorganic substances and water pass into the lower (water) layer.

In this article, we limited ourselves to examples that illustrate not just the connection between teaching chemistry and physics, but compensate for the lack of textbooks in which the named physical phenomena, as a rule, are not reflected.