USES OF OXYGEN

SECOND TERM E-LEARNING NOTES

SUBJECT: CHEMISTRY

CLASS: SS 2

SCHEME OF WORK

PERIOD 4: COMPOUNDS OF OXYGEN

Binary Compounds of Oxygen- Classification of Oxides

Based on their acid –base properties, there are four classes of oxides of elements in Periods 2 and 3: acidic, basic, amphoteric and neutral.

Acid oxides: These are of non-metals which dissolve in water to form acidic solution. And react with base to form salt and water. Examples of acid oxides are P₅O₁₀, NO₂, SO₂, SiO₂ etc. They are called acid anhydride. E.g.

CO₂ +NaOH Na₂CO₃ + H₂O

SO₃ + 2KOH K₂SO₄ + H₂O

NOTE: SiO₂ is insoluble in water

Basic oxides: They are metallic oxides that are basic in nature because they react with acids to form salt and water only. Examples are K₂O, MgO, CaO, Li₂O etc. Soluble basic oxides are called alkali. E.g.

Na₂O_(g) + H₂O_(l) 2NaOH_(aq)

Na₂O_(s) + 2HCl_(aq) 2NaCl_(aq) + H₂O_(l)

Amphoteric oxides: These are oxides that behave both like acidic and basic oxides. They react with both acid and base E.g. ZnO, Al₂O₃, PbO etc

ZnO(s) + H₂SO_4(aq) ZnSO₄ + H₂O_(l)

ZnO + 2NaOH + H₂O Na₂Zn(OH)₄

Neutral oxides: They are neither acidic nor basic in character. E.g. water, CO, N₂O

Peroxide oxides: These are higher oxides where O-O bond is present. They give hydrogen peroxide when reacted with a dilute acid. E.g. Barium peroxide BaO₂, Calcium peroxide CaO₂, Sodium peroxide Na₂O_2, Hydrogen peroxide H₂O₂ (most common).

USES OF OXYGEN

1. It is used in oxy-hydrogen for welding and cutting of metals. A mixture of hydrogen and oxygen can burn to produce a temperature of 2,500
2. In oxy- ethyne [oxy-acetylene] flame for welding and cutting of steel. The reaction is highly exothermic.
3. In respiration by plants and animals.
4. As breathing aids in hospitals, high altitude flying and sea- dividing.
5. In steel production by Linz- Donawitz [L-D] process.
6. Liquefied oxygen is used in explosives, and as a rocket fuel

The Ozone Layer and Green House Effect

The ozone layer or ozone shield is a region of Earth’s stratosphere that absorbs most of the Sun’s ultraviolet (UV) radiation. It contains high concentrations of ozone (O₃) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth’s atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometres (12 to 19 mi) above Earth, although its thickness varies seasonally and geographically. It has been ascertained through observation from satellites, that the ozone layer has been depleted more over the Antartic and there is now the creation of ‘ozone hole’. This depletion or reduction in the levels of ozone in the ozone layer has caused worldwide changes in climate and sea levels caused by an increases warming of the atmosphere due to release of gases, principally, carbon(IV) oxide, CO₂, in what is termed ‘Green house effect’. Green house gases e.g. CO₂, water vapour, chlorofluorocarbons are transparent to short wave radiation, but absorb radiation at certain long wavelengths. Thus, the gases form a blanket, trapping out-going heat, much as the glass or plastic does in a green house, thereby leading to rising sea levels and general atmospheric warming, as well as melting of ice and changes in vegetation. This has led to the problems of desertification and flooding.

EVALUATION

1. State three uses of oxygen.
2. Define four types of oxide with one example each.

GENERAL EVALUATION

OBJECTIVE TEST:

1. In which group is oxygen in the periodic table? (a) IV (b) VI (c) VII (d) IV
2. Which of the following is an allotrope form of oxygen? (a) oxide (b) Ozone (c) diamond (d) graphite
3. Oxygen is prepared by heating. (a) Na₂CO₃ (b) KClO₃(c) K₂SO₄ (d) H₂S
4. The existence of two or more forms of the same element in the same physical state is known as. (a) Isotopic (b) allotropy (c) oxides (d) homologous.
5. Amphoteric oxides are oxides which (a) react with neither acids nor alkalis (b) react with both acids and alkalis (c) react with acid only (d) react base only.

ESSAY QUESTIONS

1. What is allotropy? Name an allotrope of oxygen.
2. Name the four classes of oxygen and give example of each class.
3. Describe the commercial preparation of oxygen.
4. Describe simple test to distinguish between oxygen and nitrogen(I)oxide
5. Name the product formed when the following are burnt in oxygen:
6. Carbon (ii) sulphur (iii) phosphorous (iv) magnesium.

PRE READING ASSIGNMENT

Read about halogens.

WEEKEND ACTIVITY:

Describe the manufacturing of chlorine by the electrolysis of brine. State clearly the products liberated at the various electrodes and why these products were preferred.