Test "Nitrogen and its compounds"

Option 1 1. The strongest molecule a) H 2; b) F 2 ; c) O 2; d) N 2 . 2. Phenolphthalein color 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. During thermal decomposition of copper (II) nitrate, the following are formed:a) copper (II) nitrite and O 2 ;b) nitric oxide(IV) and O 2 ;c) copper(II) oxide, brown gas NO 2 and O 2 ; d) copper (II) hydroxide, N 2 and O 2. 5. Which ion is formed by the donor-acceptor mechanism? a) NH 4 + ; b) NO 3 - ; c) Cl - ; d) SO 4 2–. 6. Specify 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 (razb.); b) Cu + HCl (solution); c) Al + NaOH + H 2 O; d) Zn + H 2 SO 4 (razb.); e) Fe + HNO 3 (conc.). 8. Write an equation for the reaction of zinc with very dilute nitric acid if one of the reaction products is ammonium nitrate. Specify the coefficient in front of the oxidizing agent. 9.

Name the substances A, B, C. Option 2 1. It is impossible to collect by the method of displacement of water: 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. When interacting with HNO 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 produces: 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. The degree of nitrogen oxidation in ammonium sulfate: a) -3; b) -1; c) +1; d) +3. 6. With which of the following substances does concentrated HNO react? 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 an equation for the interaction of magnesium with dilute nitric acid if one of the reaction products is a simple substance. Specify the coefficient in the equation in front of the oxidizing agent. 9. Write reaction equations for the following transformations:

Name the substances A, B, C, D.

Answers

Option 1 1 - G; 2 - a; 3 - G; 4 - in; 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 - in; 3 - in; 4 - b; 5 - a; 6 – a, e; 7 - in,

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) Grade 8

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

• Obtaining and properties of oxygen,
• "Preparation of salt solutions with a certain mass fraction of the dissolved substance",
• "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 are tested by me in the classroom. They can be used in the study of the school course of chemistry 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 type of independent work. The experiment not only enriches students with new concepts, skills, skills, but also is a way to verify 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 in the 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. Be able to receive oxygen in the laboratory and collect it by two methods: air displacement and water displacement; confirm experimentally the properties of oxygen; know the safety rules.
Equipment. A metal stand with a foot, a spirit lamp, matches, a test tube with a gas outlet tube, a test tube, a ball of cotton wool, 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), Ca (OH) 2 lime water, charcoal,
Fe (steel wire or paper clip).

Safety regulations.
Handle chemical equipment with care!
Remember! The test tube is heated, holding it in an inclined position, along its entire length with two or three movements in the flame of an alcohol lamp. When heating, point the opening of the test 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, while simultaneously using the materials of 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 goal, list the equipment and reagents, draw up a table for the report.

DURING THE CLASSES

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

M.V. Lomonosov

Obtaining oxygen
air displacement method

(10 min)

1. Potassium permanganate (KMnO 4) place in a dry test tube. Place a loose ball of cotton wool at the opening of the test tube.
2. Close the test tube with a stopper with a gas outlet tube, check for tightness (Fig. 1).

Rice. one. Instrument check for tightness

(Teacher's explanations on how to check the device for leaks.) Fix 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. Warm up the substance in the test tube. (Remember safety regulations.)
5. Check for the presence of gas with a smoldering splinter (charcoal). What are you watching? Why can oxygen be collected by air displacement?
6. Collect the resulting oxygen in two flasks for the following experiments. Close the flasks with stoppers.
7. Prepare a report using the table. 1, which you place on the spread of your notebook.

Obtaining oxygen
water displacement method

(10 min)

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

2. When the oxygen has forced the water out of 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, continuing to heat the tube with KMnO 4 . If this is not done, then the water will be thrown into a hot test tube. Why?

Combustion of coal in oxygen

(5 minutes)

1. Fix the coal on a metal wire (dissecting needle) and bring it into the flame of an alcohol lamp.
2. Lower the red-hot coal into the flask with oxygen. What are you watching? Give an explanation (Figure 4).

3. After removing the 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. Issue a report on the work in the 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. Immerse the wire with the burning match into the flask with oxygen. What are you watching? Give an explanation (Figure 5).

2. Issue a report on the work in the table. one.

Table 1

Operations in progress (what they were doing)	Figures with designations of initial and received substances	Observations. Terms carrying out reactions. Reaction equations	Explanations of observations. conclusions
Assembly of the device for obtaining oxygen. Checking the device for leaks
Obtaining oxygen from KMnO 4 when heated
Proof of oxygen production with smoldering splinter
Characteristics of the physical properties of O 2. Collecting 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 general conclusion about the work done (5 min).

CONCLUSION. One of the ways to obtain oxygen in the laboratory is the decomposition of KMnO 4 . Oxygen is a colorless and odorless gas, 1.103 times heavier than air ( M r(O 2) \u003d 32, M r(air) \u003d 29, from which follows 32/29 1.103), slightly soluble in water. It reacts with simple substances, forming oxides.

Put the workplace in order (3 min): disassemble the appliance, arrange the dishes and accessories in their places.

Submit your notebooks for review.

Homework.

A 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) to Fe 3 O 4

Solution

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

M r(Fe 2 O 3) \u003d 56 2 + 16 3 \u003d 160,

(Fe) \u003d 56 2/160 \u003d 0.7,
(Fe) = 70%,

M r(Fe 3 O 4) \u003d 56 3 + 16 4 \u003d 232,
"(Fe) \u003d 56 3/232 \u003d 0.724,
"(Fe) = 72.4%.

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

During practical work, the teacher monitors the correctness of the performance of techniques and operations by students and notes in the skill record card (Table 2).

table 2

Skill record card

Operations of practical work	Surnames of students
	BUT	B	AT	G	D	E
Assembly of the device for obtaining oxygen
Checking the device for leaks
Fixing the test tube in the leg of the tripod
Alcohol lamp handling
Heating a test tube with KMnO 4
Checking the release of O 2
Collecting O 2 in a vessel by two methods: air displacement, water displacement
coal burning
Combustion of Fe (steel wire)
Experimental culture
Making work in a notebook

Sample report on the practical work done (Table 1)

O 2 is obtained in the laboratory by decomposition of KMnO 4 when heated Proof of obtaining oxygen by means of
smoldering splinter smoldering splinter
(charcoal) lights up brightly
in O 2 The resulting gas O 2 supports combustion Characteristic
physical properties of O 2. Collecting 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, so
it is collected in a vessel placed on the bottom. Oxygen is slightly soluble in water Characteristics of the chemical properties of O 2. Interaction with simple substances: combustion of coal (a), combustion of iron (steel wire, paper clip, shavings) (b)

A red-hot coal burns brightly in O 2:

Lime water becomes cloudy, because a water-insoluble precipitate of 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

When preparing 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 obtaining, their recognition and application). Having studied the topics of the specification of the exams of the OGE and the USE (on the websitewww. fipi. en ), we can say that there is practically no separate issue on gaseous substances (see table):

USE

№14 (Characteristic chemical properties of hydrocarbons: alkanes, cycloalkanes, alkenes, dienes, alkynes, aromatic hydrocarbons (benzene and toluene). Main methods for obtaining hydrocarbons (in the laboratory);№26 (Rules for working in the laboratory. Laboratory glassware and equipment. Safety rules for working with caustic, combustible and toxic substances, household chemicals. Scientific methods for studying chemicals and transformations. Methods for separating mixtures and purifying substances. The concept of metallurgy: general methods for 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 compounds Polymerization and polycondensation reactions Polymers Plastics, fibers, rubbers)

So, in option No. 3 (Chemistry. Preparation for the OGE-2017. 30 training materials according to the demo version of 2017. Grade 9: teaching aid / edited by V.N. Doronkin. - Rostov n / D: Legion, 2016. - 288 p.), students were 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 correct

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 the method of water displacement. Oxygen dissolves in water, but does not interact with it. Therefore, it can be obtained by the method of water displacement.

In option No. 4 (Chemistry. Preparation for the Unified State Examination-2017. 30 training options for the demo version for 2017: educational and methodological manual / edited by V.N. Doronkin. - Rostov n / D: Legion, 2016. - 544 p. ) students are 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, the guys need to know what is the raw material for obtaining one or another gaseous substance. For example, in the same book, edited by Doronkin, question No. 26 (option 8) sounds like this:

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

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

Answer:

In option No. 12, students are asked to recall the scope of some gaseous substances:

Establish a correspondence between the substance and its scope: for each position indicated by a letter, select the corresponding position indicated by a number:

Answer:

With the guys taking the exam in chemistry in the 9th grade, in the preparation for the exam, we fill out the following table (in the 11th grade we repeat it 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 "explosive gas"

1. By the 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 ( conc ) + 6H 2 O = 2Na + 3H 2

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

2H 2 O=2H 2 + O 2

According to the characteristic sound of the explosion: a vessel with hydrogen is brought to the flame (deaf clap - pure hydrogen, "barking" sound - hydrogen mixed with air):

2H 2 + O 2 2H 2 O

Hydrogen burner, margarine production, rocket fuel, production of various substances (ammonia, metals, e.g. 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; more soluble in water 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 Bertolet 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. Photosynthesis process:

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

The flash of a smoldering splinter in a container of oxygen

In metallurgy, as an oxidizer for rocket fuel, in aviation for breathing, in medicine for breathing, in blasting, 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. Limestone calcination industry:

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 clouding 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. You can not inhale for a long time, because. he is poisonous. Easily liquefies at normal pressure and temperature -33.4 about C. When liquid ammonia evaporates from the environment, a lot of heat is absorbed, so ammonia is used in refrigeration. Highly soluble in water: at 20 about C About 710 volumes of ammonia dissolve in 1 volume of water.

1. In industry: at high temperatures, pressure 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) by changing the color of wet phenolphthalein paper (turned 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) receiving explosives; 6) in medicine and in everyday life (ammonia)

Ethylene

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

1) In the ethane dehydrogenation industry:

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

2) Ethylene is produced in the laboratory 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 alumina and concentrated sulfuric acid are used as a catalyst):

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

Oxygen

+

upside down

+

Bottom up

Carbon dioxide

+

upside down

-

Ammonia

+

Bottom up

-

Ethylene

+

Upside down and slanted

-

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

Gathering gases

The methods of collecting gases are determined by their properties: solubility and interaction with water, air, poisonousness of the gas. There are two main methods of gas collection: air displacement and water displacement. Air displacement collect gases that do not interact with air.

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

On fig. 3a shows the collection of a gas with an air density greater than unity, such as nitric oxide (IV), whose air density is 1.58. On fig. 3b shows the collection of gas with an air density of less than unity, such as hydrogen, ammonia, etc.

By displacing water, gases are collected that do not interact with water and are poorly soluble in it. This method is called collecting gas above the 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 hole 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 the water can be collected in test tubes, which, like the cylinder, are filled with water, closed with a finger and overturned into a glass or glass bath with water.

Toxic gases are usually collected by displacing 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 the method of air displacement, then for this proceed as follows (Fig. 3, d).

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

Experience 1. Obtaining and collecting oxygen

Assemble the installation according to fig. 4. Place 3-4 g of potassium permanganate into a large dry test tube, close with a stopper with a gas outlet tube. Fix the test tube in the rack obliquely with the hole slightly up. Next to the tripod on which the test tube is mounted, place the crystallizer with water. Fill an empty test tube with water, close the hole with a glass plate and quickly turn it upside down into the crystallizer. Then in the water, take out the glass plate. There should be no air in the test tube. Heat potassium permanganate in a burner flame. Dip the end of the gas outlet tube into the water. Observe the appearance of gas bubbles.

A few seconds after the start of bubbles, put the end of the gas outlet tube into the hole of the test tube filled with water. Oxygen displaces water from the tube. After filling the test tube with oxygen, cover its opening with a glass plate and turn it upside down.

Rice. 4. Device for obtaining oxygen Put a smoldering flame into a test tube with oxygen.

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

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

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

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

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

Assemble the apparatus, consisting of a test tube with a stopper, through which a glass tube with a retracted end passes (Fig. 5). Place a few pieces of zinc in a test tube and add a dilute solution of sulfuric acid. Firmly insert the stopper with the tube pulled back, fix the test tube vertically in the tripod clamp. Observe gas evolution.

Rice. 5. Device for producing hydrogen The hydrogen escaping through the tube must not contain air impurities. Put a test tube turned upside down on the gas outlet tube, remove it after half a minute 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 when tanning).

If air is present 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 comes out of the device, light 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 the corresponding reaction equations.

2. Write an equation for the chemical reaction to produce hydrogen under experimental conditions.

3. Hold a dry tube over the hydrogen flame. What substance is produced by burning hydrogen? Write the equation for the hydrogen combustion reaction.

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

Experience 3. Getting ammonia

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 its bottom is slightly higher than the hole. Close the test tube with a cork with a gas outlet tube, on the curved end of which put the test tube upside down. Gently heat the test tube with the mixture. Place a piece of litmus paper soaked in water to the opening of the inverted test tube. Note the color change on the litmus paper.

Control questions and tasks:

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

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

3. Write an equation for 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 the flask, pour 5-10 ml of concentrated nitric acid into the funnel. Pour acid into the flask in small portions. Collect the escaping gas in a test tube.

Rice. 7. Device for obtaining nitric oxide (IV)

Control questions and tasks:

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

2. Write an equation for the reaction of the interaction of copper with 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 products of HNO 3 reduction are NO 2 , NO, N 2 O, NH 3 .

Experience 5. Getting hydrogen chloride

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

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

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

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

Rice. 8. Device for producing hydrogen chloride stop heating the flask, and lower the end of the gas outlet tube into a flask with water (keep the tube close above the water, without lowering it into the water). After removing 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 paper. 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. Obtaining 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 purify passing carbon monoxide (IV) from hydrogen chloride and mechanical impurities, bottle 3 - sulfuric acid for gas drying) and flasks 4 with a capacity of 250 ml for collecting carbon monoxide (IV) (Fig. 9).

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

Control questions and tasks:

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

2. Write an equation for the formation of carbon monoxide (IV).

3. Is it possible to use a concentrated solution of sulfuric acid to obtain carbon monoxide (IV)?

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

Test questions:

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

2. Propose a classification of gases according to 4-5 essential features.

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 conditional air, in which the mass fraction of oxygen is 23%, and nitrogen is 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 argon with a volume of 56 liters and nitrogen with a volume of 28 liters. The volumes of gases are given to n.o.s.

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

Analysis of the distribution of physical forces
when using chemicals

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 using the drawing of the device: what is moving where and what is happening where.

One of the instruments in the chemistry lab is a gasometer. On fig. 1 shows a gasometer filled with gas. It can be oxygen, as indicated in the figure, carbon dioxide, or simply air. Cranes 1 and 2 closed at this moment. Gas in accordance with Pascal's law exerts pressure on the walls of the vessel and water. Opening the faucet 1 , the column of water from the funnel puts pressure on the gas, squeezing it, but since internal gas pressure and water pressure are balanced, nothing happens. Opening the faucet 2 , the gas rushes into the outlet (the flow rate is adjusted by carefully turning the cock). The pressure inside the vessel drops - and water from the funnel enters the gasometer. After the faucet is closed 2 gas extraction is stopped, the water level is set at a higher level, because. there is a new balance of power. Turn off the tap to stop the water pressure 1 .

The second device, similar to a gasometer, 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 condition, the tap is open. A strong solution of hydrochloric acid rushes into the lower part of the device, fills it and wets the zinc metal lying on the copper grid. Zinc dissolves in acid, reacts with it, the resulting hydrogen rushes into the middle sphere of the device, displaces air, mixing with it. Therefore, the outgoing gas must be checked for purity. The distribution of physical forces in the device is shown in fig. 2 with arrows.

We close the tap. Hydrogen continues to form, its quantity increases. Since the gas outlet is blocked, the pressure inside the sphere increases. It squeezes the acid out of the middle sphere until the acid no longer covers the surface of the zinc. The chemical reaction stops (zinc wetted with acid continues to react with it for some time). The internal pressure in the device, created by hydrogen, and the pressure created by the hydraulic seal, are balanced.

Consider the methods of collecting gases. On fig. 3 shows how to collect gas by 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 the jar or beaker, displace the air.

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

The device shown in fig. 5, students collect on the practical work "Obtaining oxygen and studying its properties." This instrument illustrates the method of collecting gas by displacing air (a physical justification for the concept of "relative density").

Another way 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). Gas from the reactor 1 enters the gas pipe 2 placed under an upside down cylinder 3 . Passing through the water column, the gas is collected in the area of ​​the bottom of the cylinder. The pressure of the gas pushes the water out of the cylinder.

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

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

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

If you saturate with hydrogen chloride from a test tube (with reagents) with a gas outlet pipe lowered into water (Fig. 10), then the first portions of the gas instantly dissolve in water. About 500 liters of hydrogen chloride are dissolved in 1 liter of water, therefore, the incoming gas does not create excess pressure. On fig. 10 marked sequential change in gas pressure p internal in the reaction tube relative to atmospheric pressure p atm. The pressure inside the device becomes less than the external pressure, and water rapidly fills the gas outlet tube and the device itself. In addition to the fact that the experiment is ruined, the test tube can also crack.

When studying the chemical properties of metallic sodium (Fig. 11), it is important not only to observe its behavior in the 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 unity (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. The reaction of interaction of sodium with water is exothermic. The heat released is enough to melt sodium, therefore, it is a fusible metal. The fourth observation is that the reaction is accompanied by flashes, therefore, the heat of reaction is sufficient for spontaneous combustion of sodium and for a 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 a hydrogen explosion cannot be avoided. To avoid an explosion, the reaction is carried out in a crystallizer or in a beaker with a large diameter 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 bottom flask. Everything else is shown in Fig. 12.

The formation of physical and chemical 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, a seam is obtained. In autogenous cutting, the flame melts the metal, and excess oxygen burns it out.

Not every chemistry classroom has silicon as a simple substance. Let's check it for electrical conductivity using the simplest device: a probe with elastic elongated iron ends, a light bulb (mounted on a stand), and an electrical wire with a plug (Fig. 14). The light bulb glows, but not brightly - it is clear that silicon conducts 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 (like diamond) crystal lattice (atomic) with a tetrahedral orientation of chemical bonds. In diamond, covalent bonds are strong; it does not conduct electricity. In silicon, as even a rough experiment shows, some part of the electron pairs is depaired, which causes some electrical conductivity of the substance. In addition, silicon is heated (some students have the opportunity to verify this), which also indicates the resistance of the substance to electric current.

With great interest, students observe 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. We mix this stratified mixture with intensive shaking, we get a "gray" emulsion. Fix the test tube in a vertical position. Students observe the gradual stratification of benzene and water, and at first the lower level of the content becomes transparent, and after a short time we get the initial distribution. Water molecules are lighter than benzene molecules, but its density is slightly higher. The interaction between non-polar benzene molecules and polar water molecules is negligible, very weak, so most of the benzene is pushed to the surface of the water (see Fig. 15, b).

Now we add benzene to a few milliliters of bromine water (small intensity of staining) (see Fig. 15, b). Liquids do not mix. Intensively mix the contents of the test tube and allow the system to settle. Bromine, previously dissolved in water, is extracted into the benzene layer, as can be seen from the change in color and 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 becomes discolored, and the formed inorganic substances and water pass into the lower (aqueous) layer.

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