Give reason for the following. Hydrogen is used as a fuel in space rockets.

Hydrogen is used as a fuel in space rockets because a mixture of liquid oxygen and hydrogen produces a tremendous amount of energy. Hydrogen is light and burns with very high intensity thus becomes an excellent rocket propellant.

Give reason for the following. Hydrogen is used to weld metals.

Hydrogen prevents oxidation and contamination by carbon or oxygen and nitrogen and thus makes a protective layer around the metal. Contamination by nitrogen, oxygen or carbon may lead to loss of several properties of metals. Therefore, hydrogen is used to weld metals.

Give reason for the following. Hydrogen is added to vegetable oils.

Hydrogen converts vegetable oil into vegetable ghee by hydrogenation. Thus, unsaturated fat is converted to saturated fat by the conversion of double bonds to single bonds. Therefore, hydrogen is added to vegetable oils.

What happens when: An electric current is passed through acidified water?

When an electric current is passed through acidified water, it decomposes to give hydrogen and oxygen gas. The hydrogen gas is obtained at the cathode and the oxygen gas is obtained at the anode. 2 H 2 O → 2 H 2 + O 2

What happens when: Hydrogen combines with calcium.

Hydrogen can easily combine with calcium to form the corresponding hydride i.e. calcium hydride. This reaction takes place at a temperature of 500 ° C - 700 ° C . This is an example of combination reaction. Ca + H 2 → CaH 2