PRACTICAL WORK (1 hour) 8TH GRADE

The work is carried out by students independently under the supervision of the teacher.
I offer the result of my many years of work on preparing and conducting practical work in secondary school in 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 new program O.S. Gabrielyan, and according to the program of G.E. Rudzitis, F.G. Feldman.
Student experiment is a type 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 empirically 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, associated with 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).

(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 unburnt 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

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?

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

Sample report on practical work done (Table 1)

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:

8th grade PRODUCTION AND PROPERTIES OF OXYGEN

(practical work No. 3)

Goals: consolidate knowledge about methods of production and properties of oxygen; to develop in students new skills in the use of laboratory equipment, to teach how to collect oxygen using the air displacement method and the water displacement method, to recognize it and prove its properties, and to make observations; draw instrument drawings, draw up reaction equations, draw conclusions, follow safety rules.

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

Movelesson

I. Preparation for practical work.

Safety instructions when working with dry fuel.

Technical briefing on practical work.

IIUpdating knowledge

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

Describe the scheme for obtaining ABOUT 2

How to check that pure oxygen is obtained? (Burningsplinter.)

Students do the work using the instruction manualNika (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.

Assemble it using the 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 leaks.

Get oxygen.

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

check with a smoldering splinter.

Burn charcoal in oxygen.

III. Consolidation of knowledge, skills and abilities.

After completing the work, draw a conclusion, write down all the results in a notebook, and record the work report in the table:

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

Practical work No. 3

Production and properties of oxygen.

Goal of the work: learn to use laboratory equipment and glassware to obtain, collect and prove the presence of oxygen, learn how to obtain and collect oxygen in the laboratory, and Chemical properties oxygen.

Equipment and reagents: laboratory stand, foot, alcohol lamp, matches, test tube, stopper with gas outlet tube, splinter, spoon for burning substances, cylinder, beaker, crystallizer with water, cotton wool, potassium permanganate (solid) KMnO 4, coal, sulfur, lime water Ca (OH) 2

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.

Progress:

Experiment 1. Obtaining and collecting oxygen

a) Collection of oxygen by air displacement method

1. Assemble the device as shown in the figure:

1 - glass wool, 2 - air

To do this, secure the test tube with potassium permanganate KMnO 4 in the leg of the tripod, close it with a stopper with a gas outlet tube, the end of which is lowered into an empty beaker.

1. Check that the glass is completely filled with oxygen using a smoldering splinter.
2. In your notebook for practical work, make a drawing of the device. Write down the observations and equation for the reaction producing oxygen.

b) Collection of oxygen by water displacement method

1. Assemble the device for producing oxygen as shown in the figure:

1 - glass wool, 2 - water

To do this, secure the test tube with potassium permanganate KMnO 4 in the claw, close it with a stopper with a gas outlet tube, the end of which is lowered into an inverted measuring cylinder placed in a crystallizer with water.

1. Warm the entire test tube with the flame of an alcohol lamp, then continue heating the bottom of the test tube for 5-6 minutes.
2. In your notebook for practical work, make a drawing of the device. Record your observations. Conclude in what ways oxygen can be collected in the laboratory.

Experiment 2. Study of the properties of oxygen

a) Combustion of carbon in oxygen

Place a piece of charcoal in a spoon for burning substances and heat it in the flame of an alcohol lamp. Then place a spoonful of smoldering coal into a vessel with oxygen and watch what happens. Write down your observations in your notebook. When the burning stops, pour a little lime water into the vessel and shake. Record your observations in your notebook. Write down the equation for the combustion reaction of coal.

b) Combustion of sulfur in oxygen (The experiment is carried out in a fume hood!)

Place a piece of sulfur in an iron spoon and set it on fire in the flame of an alcohol lamp. Observe how sulfur burns in air. Then place the burning sulfur in a vessel with oxygen. Write down the observations and equation for the sulfur combustion reaction.

Write a report about the work done using the table.

Make it common conclusion at work, based on the purpose of the work.

Tidy it up your workplace.

Practical work

“Oxygen production and study of its properties”

Safety precautions: Follow the rules for working with glassware and an alcohol lamp.

General conclusion: Oxygen is a gas, without color, taste, smell, __________________________________________________________

Practical work

Observations

Conclusions and answers

Considered the mixture

It contains salt crystals of ___________ color and particles of river sand of ____________ color.

Is it a homogeneous or heterogeneous mixture?

Part of the given mixture was placed in a glass, water was poured in and stirred with a stick.

A cloudy solution formed. Over time _____________________________________

___________________________________.

In water ___________ dissolves, ______ _______________ does not. Why do you need to change

sew the solution?

Prepared filter

The filter was made from ____________ paper

We filtered the solution

Particles __________ remained on the filter. The filtrate collects in the glass

In the filtrate __________________.

Part of the filtrate was evaporated

As it evaporates on the walls of the cup, ______________________________.

Evaporation is one of the ways to separate which mixtures?

General conclusion: Using the following methods for separating mixtures: ____________________________________ purified table salt from river sand.

Practical work No.

Main classes of inorganic compounds

Practical work

"Determination of solution environment"

Safety precautions. Exercise caution when working with glassware and reagents. Do not allow reagents to come into contact with hands, clothes, or tables.

Instructions.

1. Before you begin, think carefully about your actions.
2. Read the instructions carefully:

• The test tubes provided contain water, acid and alkali;
• Using universal indicator paper, determine which medium is in which tube;
• Confirm your conclusion using the indicator phenolphthalein and methyl orange.
• Prepare the report in the form of a table.

Conclusion: test tube No. 1 contains ____________, because Wednesday __________, ...