PRACTICAL WORK (1 hour) 8TH GRADE
The work is carried out by students independently under the supervision of the teacher.
I present the result of my many years of work on preparing and conducting practical work in a secondary school during chemistry lessons in grades 8–9:
- “Preparation and properties of oxygen”,
- “Preparation of salt solutions with a certain mass fraction of 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 were tested by me in the classroom. They can be used when studying a 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 type of independent work. The experiment not only enriches students with new concepts, skills, and abilities, but is also a way to test the truth of the knowledge they have acquired, contributes to a deeper understanding of the material, and 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 obtain oxygen in the laboratory and collect it using two methods: air displacement and water displacement; confirm experimentally the properties of oxygen; know 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 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), lime water Ca(OH) 2, charcoal,
Fe (steel wire or paper clip).
Safety regulations.
Handle chemical equipment with care!
Remember! The test tube is heated by 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 studying the content of the upcoming work according to instructions, while simultaneously using materials from 8th grade textbooks by O.S. Gabrielyan (§ 14, 40) or G.E. Rudzitis, F.G. Feldman (§ 19 , 20). In notebooks for practical work, write down the name of the topic, the purpose, list the equipment and reagents, and draw up a table for the report.
DURING THE CLASSES
I put one experience above
than a thousand opinions
born only
imagination.
M.V. Lomonosov
Obtaining oxygen
air displacement method
(10 min)
1. Place potassium permanganate (KMnO4) 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 and check for leaks (Fig. 1).
|
Rice. 1.
|
(Explanations from the teacher on how to check the device for leaks.) Secure 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 safety rules.)
5. Check for the presence of gas with a smoldering splinter (charcoal). What are you observing? Why can oxygen be collected by air displacement?
6. Collect the resulting oxygen in two flasks for the following experiments. Seal the flasks with stoppers.
7. Complete the report using the table. 1, which you place on the spread of your notebook.
Obtaining oxygen
water displacement method
(10 min)
1. Fill the test tube with water. Close the test tube with your thumb and turn it upside down. In this position, lower your hand with the test tube into the crystallizer with water. Place a test tube at the end of the gas outlet tube without removing it from the water (Fig. 3).
2. When oxygen displaces the water from the test 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 while continuing to heat the test tube with KMnO4. If this is not done, the water will transfer into the hot test tube. Why?
Combustion of coal in oxygen
(5 minutes)
1. Attach a coal to a metal wire (dissecting needle) and place it into the flame of an alcohol lamp.
2. Place a hot coal into a flask with oxygen. What are you observing? 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 observing? Give an explanation.
4. Prepare a work report in the table. 1.
Burning steel (iron) wire
in oxygen
(5 minutes)
1. Attach a piece of match to one end of the steel wire. Light a match. Place a wire with a burning match into a flask with oxygen. What are you observing? Give an explanation (Figure 5).
2. Prepare a work report in the table. 1.
Table 1
| Operations Performed (what they were doing) |
Drawings with designations of starting and obtained substances | Observations. Conditions carrying out reactions. Reaction equations |
Explanations of observations. conclusions |
|---|---|---|---|
| Assembling a device for producing oxygen. Checking the device for leaks | |||
| Obtaining oxygen from KMnO 4 when heated |
|||
| Proof of obtaining oxygen using smoldering splinter |
|||
| Characteristics of the physical properties of O 2. Collection of O 2 using two methods: by displacing air, by displacing water |
|||
| 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 ( Mr(O 2) = 32, Mr(air) = 29, which implies 32/29 1.103), slightly soluble in water. Reacts with simple substances, forming oxides.
Put your workplace in order (3 min): disassemble the device, put dishes and accessories in their places.
Submit your notebooks for checking.
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)/ Mr, Where n– the number of atoms of element X in the formula of the substance.
Mr(Fe 2 O 3) = 56 2 + 16 3 = 160,
(Fe) = 56 2/160 = 0.7,
(Fe) = 70%,
Mr(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.
During practical work, the teacher observes the correct execution of techniques and operations by students and notes them on the skill card (Table 2).
table 2
Skill card
| Practical operations | Student names | |||||
|---|---|---|---|---|---|---|
| A | B | IN | G | D | E | |
| Assembling a device for producing oxygen | ||||||
| Checking the device for leaks | ||||||
| Strengthening the test tube in the stand leg | ||||||
| Handling an alcohol lamp | ||||||
| Heating a test tube with KMnO 4 | ||||||
| Checking O2 release | ||||||
| Collecting O2 into a vessel using two methods: by displacing air, by displacing water |
||||||
| Coal burning | ||||||
| Burning Fe (steel wire) | ||||||
| Experimentation culture | ||||||
| Preparation of work in a notebook | ||||||
Sample report on practical work done (Table 1)
smoldering splinter
(coal) lights up brightly
in O 2
physical properties of O 2. Collection of O 2 using two methods:
displacement of air(s),
by displacing water (b)
a little heavier than air, so
it is collected in a vessel placed at the bottom. Oxygen is slightly soluble in water
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:
with simple
substances - metals and non-metals. The formation of a white precipitate confirms the presence of CO 2 in the flask
Test "Nitrogen and its compounds"
Option 1 1. Strongest molecule: a) H 2; b) F 2; c) O 2; d) N 2. 2. Color of phenolphthalein in ammonia solution: a) crimson; b) green; c) yellow; d) blue. 3. Oxidation state +3 at the nitrogen atom in the compound: a) NH 4 NO 3; b) NaNO 3; c) NO 2; d) KNO 2. 4. The thermal decomposition of copper(II) nitrate produces: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) aqueous ammonia solution; d) ammonium nitrate. 7. Hydrogen is released during the interaction: a) Zn + HNO 3 (diluted); b) Cu + HCl (solution); c) Al + NaOH + H 2 O; d) Zn + H 2 SO 4 (diluted); 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. Indicate the coefficient before the oxidizing agent. 9.Give names to substances A, B, C. Option 2 1. The following cannot be collected by displacing water: a) nitrogen; b) hydrogen; c) oxygen; d) ammonia. 2. The reagent for 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. The 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. Oxidation degree of nitrogen in ammonium sulfate: a) –3; b) –1; c) +1; d) +3. 6. Which of the following substances does concentrated HNO react with? 3 under normal conditions? a) NaOH; b) AgCl; c) Al; d) Fe; e) Cu. 7. Indicate 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. Indicate the coefficient before the oxidizing agent 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, g; 7 – c, d; 8 – 10,
2Ag + + SO 4 2– = Ag 2 SO 4 ;
8 – 12, 9. A – NO, B – NO 2, C – HNO 3, D – NH 4 NO 3,
Collecting gases
Methods for collecting gases are determined by their properties: solubility and interaction with water, air, and toxicity 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.
Based on the relative density of the gas in the air, a conclusion is made on how to position the vessel for collecting gas (Fig. 3, a and b).
In Fig. 3, a shows the collection of gas with an air density of more than one, for example, nitrogen oxide (IV), whose air density is 1.58. In Fig. Figure 3b shows the collection of gas with an air density of less than one, for example 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 over 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 there are no air bubbles left in the cylinder. The plate is held by hand, the cylinder is turned over and lowered into a glass bath of water. The plate is removed under water, and a gas outlet tube is inserted into the open hole of the cylinder. The gas gradually displaces water from the cylinder and fills it, after which the hole in 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 the cylinder is placed 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 tipped into a glass or glass bath of water.
Poisonous gases are usually collected by displacing water, since in this case 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 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(IV) oxide, 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 stopper with gas outlet tubes is removed from it and the vessel is quickly closed with a stopper or glass plate, and the stopper 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 in a large dry test tube and close with a stopper with a gas outlet tube. Secure the test tube in a rack at an angle with the opening slightly upward. Place a crystallizer with water next to the stand on which the test tube is mounted. Fill the empty test tube with water, cover the hole with a glass plate and quickly turn it upside down into the crystallizer. Then take out the glass plate in the water. There should be no air in the test tube. Heat potassium permanganate in a burner flame. Place the end of the gas outlet tube in water. Observe the appearance of gas bubbles.
A few seconds after the bubbles begin to flow, place the end of the gas outlet tube into the hole of a test tube filled with water. Oxygen displaces water from the test tube. After filling the test tube with oxygen, cover its opening with a glass plate and invert it.
1. What laboratory methods for producing oxygen do you know? Write the corresponding reaction equations.
2. Describe the 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 flash in a test tube with oxygen?
Experience 2. Production of hydrogen by the action of a metal on an acid
Assemble a device consisting of a test tube with a stopper through which a glass tube with an extended end passes (Fig. 5). Place a few pieces of zinc in a test tube and add a dilute solution of sulfuric acid. Insert the stopper tightly with the tube pulled out, secure the test tube vertically in the stand clamp. Observe gas evolution.
If there is an admixture of air 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 from the device, light it at the opening of the drawn tube.
Test questions and assignments:
1. Indicate methods for producing and collecting hydrogen in the laboratory. Write the corresponding reaction equations.
2. Create an equation for the chemical reaction of producing hydrogen under experimental conditions.
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 combustion reaction of hydrogen.
4. How to check the purity of the hydrogen obtained during the experiment?
Experience 3. Ammonia production
Test questions and assignments:
1. What hydrogen compounds of nitrogen do you know? Write their formulas and names.
2. Describe the phenomena occurring. 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. Production of nitric oxide (IV)
Assemble the device according to Fig. 7. Place some copper shavings in the flask and pour 5-10 ml of concentrated nitric acid into the funnel. Pour the acid into the flask in small portions. Collect the released gas in a test tube.
Test questions and assignments:
1. Describe the phenomena occurring. What is the color of the gas released?
2. Write an 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 products of the reduction 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 a dropping funnel - a concentrated solution of sulfuric acid (Fig. 8). Insert the end of the gas outlet tube into a dry vessel to collect hydrogen chloride so that the tube reaches almost to the bottom. Cover 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.
To speed up the reaction, warm the flask slightly. When over
with the cotton wool that covers the opening of the vessel, fog will appear,
Test questions and assignments:
1. Explain the observed phenomena. What is the cause of fog formation?
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 chemical reaction equation for the interaction of solid sodium chloride with concentrated sulfuric acid.
Experience 6. Production and collection of 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, flask 3 - sulfuric acid for gas drying) and flask 4 with a capacity of 250 ml for collecting carbon monoxide (IV) (Fig. 9).
Rice. 9. Device for producing carbon monoxide (IV)
Test questions and assignments:
1. Place a lit splinter into a flask with carbon monoxide (IV) and explain why the flame goes out.
2. Write an equation for the reaction of the formation of carbon monoxide (IV).
3. Is it possible to use a concentrated solution of sulfuric acid to produce carbon monoxide?
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 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 a substance.
2. Propose a classification of gases according to 4-5 essential characteristics.
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 - 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. Gas volumes are given at standard values.
8. An open vessel is heated at a constant pressure from 17 o C to 307 o C. What fraction of the air (by mass) in the vessel is displaced?
9. Determine the mass of 3 liters of nitrogen at 15 o C and a pressure of 90 kPa.
10. The mass of 982.2 ml of gas at 100 o C and a pressure of 986 Pa is equal to 10 g. Determine the molar mass of the gas.
PRACTICAL WORK (1 hour) 8TH GRADE
The work is carried out by students independently under the supervision of the teacher.
I present the result of my many years of work on preparing and conducting practical work in a secondary school during chemistry lessons in grades 8–9:
- “Preparation and properties of oxygen”,
- “Preparation of salt solutions with a certain mass fraction of 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 were tested by me in the classroom. They can be used when studying a 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 type of independent work. The experiment not only enriches students with new concepts, skills, and abilities, but is also a way to test the truth of the knowledge they have acquired, contributes to a deeper understanding of the material, and 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 obtain oxygen in the laboratory and collect it using two methods: air displacement and water displacement; confirm experimentally the properties of oxygen; know 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 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), lime water Ca(OH) 2, charcoal,
Fe (steel wire or paper clip).
Safety regulations.
Handle chemical equipment with care!
Remember! The test tube is heated by 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 studying the content of the upcoming work according to instructions, while simultaneously using materials from 8th grade textbooks by O.S. Gabrielyan (§ 14, 40) or G.E. Rudzitis, F.G. Feldman (§ 19 , 20). In notebooks for practical work, write down the name of the topic, the purpose, list the equipment and reagents, and draw up a table for the report.
DURING THE CLASSES
I put one experience above
than a thousand opinions
born only
imagination.
M.V. Lomonosov
Obtaining oxygen
air displacement method
(10 min)
1. Place potassium permanganate (KMnO4) 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 and check for leaks (Fig. 1).
|
Rice. 1.
|
(Explanations from the teacher on how to check the device for leaks.) Secure 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 safety rules.)
5. Check for the presence of gas with a smoldering splinter (charcoal). What are you observing? Why can oxygen be collected by air displacement?
6. Collect the resulting oxygen in two flasks for the following experiments. Seal the flasks with stoppers.
7. Complete the report using the table. 1, which you place on the spread of your notebook.
Obtaining oxygen
water displacement method
(10 min)
1. Fill the test tube with water. Close the test tube with your thumb and turn it upside down. In this position, lower your hand with the test tube into the crystallizer with water. Place a test tube at the end of the gas outlet tube without removing it from the water (Fig. 3).
2. When oxygen displaces the water from the test 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 while continuing to heat the test tube with KMnO4. If this is not done, the water will transfer into the hot test tube. Why?
Combustion of coal in oxygen
(5 minutes)
1. Attach a coal to a metal wire (dissecting needle) and place it into the flame of an alcohol lamp.
2. Place a hot coal into a flask with oxygen. What are you observing? 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 observing? Give an explanation.
4. Prepare a work report in the table. 1.
Burning steel (iron) wire
in oxygen
(5 minutes)
1. Attach a piece of match to one end of the steel wire. Light a match. Place a wire with a burning match into a flask with oxygen. What are you observing? Give an explanation (Figure 5).
2. Prepare a work report in the table. 1.
Table 1
| Operations Performed (what they were doing) |
Drawings with designations of starting and obtained substances | Observations. Conditions carrying out reactions. Reaction equations |
Explanations of observations. conclusions |
|---|---|---|---|
| Assembling a device for producing oxygen. Checking the device for leaks | |||
| Obtaining oxygen from KMnO 4 when heated |
|||
| Proof of obtaining oxygen using smoldering splinter |
|||
| Characteristics of the physical properties of O 2. Collection of O 2 using two methods: by displacing air, by displacing water |
|||
| 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 ( Mr(O 2) = 32, Mr(air) = 29, which implies 32/29 1.103), slightly soluble in water. Reacts with simple substances, forming oxides.
Put your workplace in order (3 min): disassemble the device, put dishes and accessories in their places.
Submit your notebooks for checking.
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)/ Mr, Where n– the number of atoms of element X in the formula of the substance.
Mr(Fe 2 O 3) = 56 2 + 16 3 = 160,
(Fe) = 56 2/160 = 0.7,
(Fe) = 70%,
Mr(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.
During practical work, the teacher observes the correct execution of techniques and operations by students and notes them on the skill card (Table 2).
table 2
Skill card
| Practical operations | Student names | |||||
|---|---|---|---|---|---|---|
| A | B | IN | G | D | E | |
| Assembling a device for producing oxygen | ||||||
| Checking the device for leaks | ||||||
| Strengthening the test tube in the stand leg | ||||||
| Handling an alcohol lamp | ||||||
| Heating a test tube with KMnO 4 | ||||||
| Checking O2 release | ||||||
| Collecting O2 into a vessel using two methods: by displacing air, by displacing water |
||||||
| Coal burning | ||||||
| Burning Fe (steel wire) | ||||||
| Experimentation culture | ||||||
| Preparation of work in a notebook | ||||||
Sample report on practical work done (Table 1)
smoldering splinter
(coal) lights up brightly
in O 2
physical properties of O 2. Collection of O 2 using two methods:
displacement of air(s),
by displacing water (b)
a little heavier than air, so
it is collected in a vessel placed at the bottom. Oxygen is slightly soluble in water
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:
with simple
substances - metals and non-metals. The formation of a white precipitate confirms the presence of CO 2 in the flask
Kipp apparatus used to produce hydrogen, carbon dioxide and hydrogen sulfide. The solid reagent is placed in the middle spherical reservoir of the apparatus on a plastic ring liner, which prevents the solid reagent from entering the lower reservoir. Zinc granules are used as a solid reagent to produce hydrogen, carbon dioxide - pieces of marble, hydrogen sulfide - pieces of iron sulfide. The pieces of the poured solid should be about 1 cm 3 in size. It is not recommended to use powder, as the gas current will be very strong. After loading the solid reagent into the apparatus, a liquid reagent is poured through the upper neck (for example, a dilute solution of hydrochloric acid when producing hydrogen, carbon dioxide and hydrogen sulfide). The liquid is poured in such a quantity that its level (with the gas valve open) reaches half of the upper spherical expansion of the lower part. The gas is passed through for 5-10 minutes to displace the air from the apparatus, after which the gas outlet valve is closed and a safety funnel is inserted into the upper neck. The gas outlet tube is connected to the device where the gas needs to be passed.
When the tap is closed, the released gas displaces the liquid from the spherical expansion of the device, and it stops working. When the tap is opened, the acid again enters the tank with the solid reagent, and the apparatus begins to operate. This is one of the most convenient and safe methods for obtaining gases in the laboratory.
Collect gas in a vessel possible using various methods. The two most common methods are the water displacement method and the air displacement method. The choice of method is determined by the properties of the gas to be collected.
Air displacement method. Almost any gas can be collected using this method. Before sampling the gas, it is necessary to determine whether it is lighter than air or heavier. If the relative density of the gas in air is greater than unity, then the receiver vessel should be kept with the opening upward, since the gas is heavier than air and will sink to the bottom of the vessel (for example, carbon dioxide, hydrogen sulfide, oxygen, chlorine, etc.). If the relative density of the gas in air is less than unity, then the receiver vessel should be kept with the opening downward, since the gas is lighter than air and will rise to the top of the vessel (for example, hydrogen, etc.). The filling of the vessel can be controlled in different ways, depending on the properties of the gas. For example, to determine oxygen, a smoldering splinter is used, which, when brought to the edge of the vessel (but not inside!) flares up; When determining carbon dioxide, the hot torch goes out.
Water displacement method. This method can only collect gases that are insoluble in water (or only slightly soluble) and do not react with it. To collect gas, you need a crystallizer filled 1/3 with water. The receiving vessel (most often a test tube) is filled to the top with water, closed with a finger and lowered into the crystallizer. When the hole of the vessel is under water, it is opened and a gas outlet tube is inserted into the vessel. After all the water has been displaced from the vessel by gas, the hole is closed under water with a stopper and the vessel is removed from the crystallizer.
Checking gas purity. Many gases burn in air. If you ignite a mixture of flammable gas and air, an explosion will occur, so the gas must be checked for purity. The test involves burning a small portion of gas (about 15 ml) in a test tube. To do this, the gas is collected in a test tube and ignited from the flame of an alcohol lamp. If the gas does not contain air impurities, then combustion is accompanied by a slight pop. If a sharp barking sound is heard, then the gas is contaminated with air and needs to be cleaned.
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