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OXYGEN

Oxygen is a colourless, odourless and a gaseous element belonging to the VI^th group of the periodic table. In the natural state it occurs in the atmosphere, about 21% by volume. It is an essential component of all living matter. It is the most abundant element and forms about one-half of the earth’s crust ( 49.2%) . It is charecterised by

1. Atomic number 8
2. Relative atomic mass 15.9994
3. Density 1.429 g/dm³ (slightly heavier than air)
4. Melting point -214.4^OC
5. Boiling point -183^OC
6. It is soluble in water.
7. It is a supporter of combustion.
8. It is paramagnetic in nature.

PREPARATION

1. By the action of concentrated H₂SO₄ on MnO₂

2H₂SO₄ + 2MnO_{2 è} 2MnSO₄ + 2H₂O + O₂

2. In the laboratory it can be obtained by the thermal decomposition of the oxides of metals

2HgO è 2Hg + O₂

3MnO_{2 è} Mn₃O₄ + O₂

3. Commercially oxygen may be obtained by the electrolysis of acidulated water using platinum electrodes, or electrolysis of alkaline water using nickel electrodes.

CHEMICAL PROPERTIES

1. When metals and non-metals are burned in air, they form their corresponding oxides

4Na + O₂ è 2Na₂O

2Ca + O₂ è 2CaO

S + O₂ è SO₂

C + O₂ è CO₂

2. Organic compounds get oxidised when heated in the presence of oxygen

2CH₃OH + O₂ è 2HCHO + 2H₂O

USES

1. Oxy-acetylene flame is used for industrial purposes
2. It is used as an oxidising agent in several reactions.
3. Oxygen in the liquid form is an important constituent in the fuels used in rockets.

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