CHEMISTRY O LEVEL(FORM TWO) NOTES – HYDROGEN

HYDROGEN

Hydrogen is the lightest and most abundant element in the universe. It is the primary element from which the sun and stars are made.

LABORATORY PREPARATION OF HYDROGEN

Hydrogen can be prepared in the laboratory by the following method:

The reaction of dilute hydrochloric acid with zinc metal. When zinc reacts with dilute hydrochloric acid, zinc chloride and hydrogen gas are produced.

Reaction:

Zn(s) + 2HCl(l) → ZnCl₂(aq) + H₂(g)

Zinc + Hydrochloric acid → Zinc chloride + Hydrogen gas

Hydrogen is a good reducing agent.

Reducing agent – A substance that removes oxygen from a substance, e.g., metal oxides.

Reduction: The removal of oxygen from a substance.

Or

Reduction: The addition of hydrogen to a substance.

Reaction:

Oxidation: The removal of hydrogen from a substance.

Or

Oxidation: The addition of oxygen to a substance.

Industrial Manufacturing of Hydrogen

In industry, hydrogen gas is manufactured by electrolysis.

Electrolysis of Water

Electrolysis is a process in which a compound decomposes into its elements.

Reaction: Water → Oxygen + Hydrogen

2H₂O(l) → O₂(g) + 2H₂(g)

Physical Properties of Hydrogen

1. It is tasteless, colourless, and odorless.
2. It is lighter than air; therefore, it is found in the atmosphere.
3. It is only slightly soluble in water.
4. It does not support combustion.

Chemical Properties of Hydrogen

1. It combines easily with other chemical substances at high temperature.
2. It does not usually react with other elements at room temperature.
3. It is highly flammable and burns with a blue flame.
4. It reacts slowly with oxygen to produce water.
5. It is neither acidic nor basic.

Uses of Hydrogen

1. Manufacture of ammonia: Hydrogen is used in the synthesis of ammonia by reacting it with nitrogen in the presence of iron. This is done on a large scale through the Haber process.
2. Manufacture of margarine: Hydrogen is used in the manufacture of margarine.
3. Oxy-hydrogen flame: Hydrogen is used to produce an oxy-hydrogen flame. This flame can be used for welding and cutting metal.
4. Fuel: Since hydrogen is highly flammable, especially when mixed with pure oxygen, it is used as a fuel in rockets. Usually, liquid hydrogen is combined with liquid oxygen to make an explosive mixture.

REVIEW QUESTION

1 (a) By the aid of the diagram, explain the preparation of hydrogen using zinc and dilute hydrochloric acid.

(b) Give the properties and uses of hydrogen.