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 , 20). 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 minutes)

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 foot.

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 minutes)

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. Conditions carrying out reactions. Reaction equations	Explanations of observations. findings
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.

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

Given:	To find:
Fe 2 O 3, Fe 3 O 4 .	(Fe) in Fe 2 O 3, "(Fe) to Fe 3 O 4

Decision

(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

8 cells OBTAINING AND PROPERTIES OF OXYGEN

(practical work No. 3)

Goals: consolidate knowledge about the methods of obtaining and properties of oxygen; to form new skills in the use of laboratory equipment in students, to teach them to collect oxygen by the method of air displacement and the method of water displacement, to recognize it and prove its properties, to conduct observations; perform drawings of devices, draw up reaction equations, draw conclusions, follow safety rules.

Equipment and reagents: KMPO 4, coal, cotton wool, dry fuel, lime water, test tubes, cork with a gas outlet tube.

movelesson

I. Preparation for practical work.

Safety briefing when working with dry fuel.

Technical briefing on practical work.

IIKnowledge update

Name the reagents for obtaining 0 2 . (potassium permanganate, orpermanganate K.)

Describe the scheme for obtaining O 2

How to check that pure oxygen is received? (burningsplint.)

Students work according to the instructionsnickname (p. 70, work 3).

III. Carrying out practical work (according to options).

OptionI

1) Assemble the device according to fig. 24, p. 54.

Get oxygen.

Collect it by air displacement method. Completeness of filling the vessel with oxygen

check with a smoldering splinter.

OptionII

Assemble the device according to fig. 25, p. 54.

Check it for tightness.

Get oxygen.

Collect it by water displacement method. Completeness of filling the vessel with oxygen

check with a smoldering splinter.

Burn charcoal in oxygen.

III. Consolidation of knowledge, skills, abilities.

After the work, draw a conclusion, write down all the results in a notebook, enter the report on the work in the table:

	What have you been doing,	What was observed, the equations

Homework:§ 21; answer questions 11, 12 (p. 60); prepare a report on the protection of atmospheric air.