OXYGEN (PREPARATION, PROPERTIES AND ITS USES)

OXYGEN

Oxygen is the most abundant element in the earth and its outer crust. Oxygen was discovered by Scheede in 1772 and Priestly in 1774 rediscovered it. Oxygen occurs in nature in both free and combined states, much combined oxygen are found in minerals like clay, limestone and sand. This also occurs in form of water, many metallic and non-metallic oxides.

PREPARATION OF OXYGEN
There are many ways of preparing oxygen both in the laboratory and industrially.
Laboratory Preparation of Oxygen
There are two ways of preparing oxygen in the laboratory:
1. Thermal decomposition of pottassium trioxochlorate (V). This is done by heating pottassium trioxochlorate (V), which decomposes to release all its oxygen. Manganese (IV) oxide acts as catalyst which makes the reaction to occur at a lower temperature and at much faster rate;

2KClO_3(S) → KCl_(S) + 3O_{2 (g)}

2. Decomposition of hydrogen peroxide: this is the most convenient method for the preparation of oxygen. It requires no heat. Hydrogen peroxide decomposes readily in the presence of manganese (IV) oxide as catalyst to liberate oxygen;

2H₂O_2(aq)  → 2H₂O_(l)  + O_{2 (g)}

Hydrogen peroxide also reacts with acidified pottassium tetraoxomaganate (VII) solution in cold water to produce oxygen. This is an oxidation-reduction  reaction;

5H₂O_2(aq) + 2KMnO_{4 (aq)} + 3H₂SO₄ → K₂SO₄ (aq) + 2MnSO₄ (aq) +8H₂O(l) + 5O₂(g)

This method is highly recommended for use in school laboratories because it is safe and efficient. Other methods include, thermal decomposition of oxides such as mercury, silver, lead and reaction of sodium peroxide with water;

2HgO(s) → 2Hg(l) + O₂(g)

2Ag₂O(s) → 4Ag(s) + O₂(g)

PbO₂(s) → Pb(s) + O₂(g)

2Na₂O₂(s) + 2H₂O(l) → 4NaOH(aq) + O₂(g)

Physical Properties of Oxygen
1. Pure oxygen is a colorless, odorless and tasteless gas.
2. It is neutral to litmus paper.
3. It is slightly soluble in water.
4. Its density is about the same as that of air. 

Chemical Properties of Oxygen

Oxygen gas supports combustion of many substances. Metals, except mercury, silver and gold react with oxygen to form basic oxides. Examples:

4Na(s) + O₂(g) → 2Na₂O(s)

4K(s) + O₂(g) → 2K₂O(s)

2Ca(s) + O₂(g) → 2CaO

Non-metals like sulphur, carbon and phosphorous burn in oxygen to form acidic oxides which are also known as acid anhydrides, as they dissolve in water to form acids. Examples;

S(s) → O₂(g) → SO₂(g) → H₂SO₂(aq)

P₄(s) + 3O₂(g) → P₄O₄(s) → 4H₃PO₃(aq)

C(s) + O₂(s) → H₂CO₃(aq)

Hydrocarbons burn in oxygen to form carbon(IV) oxide and water

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

The oxygen we breathe in, oxidizes the carbonhydrate we eat to release energy

C₆H₁₂O₆(s) → 6CO₂(g) + 6H₂O(g) + Energy

Uses of Oxygen

1. Oxygen from air is breathed in by animals. In hospitals, pure oxygen is given to patients suffering from respiratory complaints.

2. Oxygen is used in industries for the production of oxygen-hydrogen blow pipe and oxy-ethyne flame.

3. Oxygen is also used in the manufacture of important chemical compounds like  tetraoxosulphate (VI) acid,  trioxonitrate (V) acid and ethanoic acid.

4. Oxygen is used in making steel for the removal of carbon, sulphur and phosphorous impurities.

5. Liquid oxygen and fuel are used as propellant for space rockets.