how to plan an experiment to confirm that air is a mixture;
what the symbols of chemical elements are and how to use them;
how to write the chemical reactions equations;
how to recognize basic laboratory equipment and how to use it, how to apply the safety rules in practice in the school chemical laboratory.
You will learn
to indicate the place of oxygen in the periodic table;
to give examples of the use of oxygen and oxides in everyday life;
to plan and perform an experiment to obtain oxygen and oxides.
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Oxygen
Task 1
Indicate the place of oxygen in the periodic table. What is the structure of its atom?
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Around 300 years ago air was still thought to be a chemical element or compound and not, as we know today, a gas mixture. Although nitrogen represents as much as 78% of the air volume, its exclusive presence in the atmosphere would mean total lack of life on Earth.
Oxygen is the most common element in nature. It accounts for almost half of the weight of the earth’s crust. It is a part of water, rocks, metal ores, sand.
Oxygen is essential for the life of most organisms, without it, animals and plants die. Decreasing its content in the air from 21 to 15% causes disruption of the body's work, and a drop below 10% may lead to death. Interestingly, in 2010, European scientists discovered the first larger multicellular organisms that do not need oxygen to live. Previously unknown species were found in sediments located in the seabed of the Mediterranean Sea.
Oxygen – obtaining
Oxygen was discovered around 1774 by an Englishman Joseph Priestley and, independently, also by the Swede Karl Scheele. As a result of heating the mercury(II) oxide, gas was emitted and droplets of mercury were deposited on the walls of the vessel. The resulting combustion sustaining gas was oxygen. Watch the film from the e‑textbook, note the origin of the name “oxygen”.
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In the laboratory, oxygen is obtained in a slightly different way.
Task 2
Watch the film. Note how oxygen can be obtained.
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Obtaining oxygen from potassium manganate(VII)1
Experiment 1
Research problem
Can oxygen be produced using potassium manganate(VII)()? How can it be identified?
Hypothesis
Oxygen can be obtained by heating potassium manganate(VII)(), as it is obtained from the thermal decomposition of mercury(II) oxide. The gas produced can be identified by means of a burning wooden skewer.
Oxygen is obtained during thermal decomposition of potassium manganate(VII), hydrogen peroxide decomposition (in the presence of a catalyst) or water decomposition due to an electric current (water electrolysis). The industrial method of obtaining oxygen is to distil liquid air.
You will need
stand,
metal holder,
2 test tubes,
plug with an integrated discharge pipe,
crystallizer,
burner,
potassium manganate(VII).
Instruction
Place a few potassium manganate(VII) crystals in the test tube. Close the test tube using the plug with the discharge tube.
Fill the second test tube with water, close its mouth with your finger and place it, upside down, in the crystallizer filled with water.
Heat the test tube with potassium manganate(VII) in the burner’s flame.
When gas is released, insert the discharge tube into a water‑filled test tube.
Once the gas has been collected in the test tube placed upside‑down, close the tube with the plug and remove it.
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Summary
When potassium manganate(VII) is heated, a gas is released that displaces water from the tube. The gas collected in the test tube is colorless. It is a decomposition reaction. This reaction resulted in a colorless and odorless gas.
Obtaining oxygen from hydrogen peroxide in the presence of yeast1
Experiment 2
Research problem
Does the food yeast allow the decomposition of hydrogen peroxide? How can you identify the gaseous product?
Hypothesis
Yeast causes the decomposition of the hydrogen peroxide solution, allowing identification of the collected oxygen with a burning wooden skewer.
Pour hydrogen peroxide to the flask, add a teaspoon of yeast or diced raw potato.
After a while place a burning wooden skewer in the flask.
Observe the changes that occur.
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Summary
As a result of decomposition of hydrogen peroxide(), under the influence of the enzymes contained in the yeast/ potato, a colorless and odorless gas is produced which can be identified by means of a burning wooden skewer.
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Exercise 1
Conclusion
Oxygen is the most common element in nature.
Oxygen is a colorless, odorless, slightly soluble in water, chemically active gas.
Oxygen can be obtained during thermal decomposition of potassium manganate(VII), hydrogen peroxide decomposition (in the presence of a catalyst) or water decomposition due to an electric current (water electrolysis).
The industrial method of obtaining oxygen is to distil liquid air.
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Homework
Task 3.1
Omów fizyczne i chemiczne właściwości tlenu i azotu
Omów fizyczne i chemiczne właściwości tlenu i azotu
Present the physical and chemical properties of oxygen and nitrogen in a table.
Keywords
oxygen, obtaining oxygen, air
Glossary
oxide
oxide
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tlenek – związek, w którym tlen jest związany z innym pierwiastkiem chemicznym, np.: , , , ,
combustion
combustion
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spalanie – reakcja chemiczna przebiegająca między materiałem palnym lub paliwem a utleniaczem, z wydzieleniem ciepła i światła
hydrogen peroxide
hydrogen peroxide
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nadtlenek wodoru (HIndeks dolny 22OIndeks dolny 22, woda utleniona) – najprostszy nadtlenek (związek z pojedynczym wiązaniem tlen‑tlen); jest stosowany jako utleniacz, środek wybielający i antyseptyczny