Q.Give the uses of hydrogen.

Hydrogen's key uses span fertiliser and fuel manufacture, edible-oil hydrogenation, welding, metallurgy, and fuel cells.

Hydrogen is used across a wide range of industrial and everyday applications:

1. Manufacture of ammonia: hydrogen reacts with nitrogen under the Haber process (N2 + 3H2 <=> 2NH3, high pressure, Fe catalyst) to produce ammonia, the basis of the nitrogenous fertiliser industry (urea, ammonium sulphate, etc.).

2. Hydrogenation of vegetable oils: hydrogen is added catalytically (Ni catalyst) to unsaturated vegetable oils to convert them into solid/semi-solid fats, producing vanaspati ghee and margarine.

3. Manufacture of chemicals: hydrogen is a key feedstock for manufacturing methanol (from synthesis gas/water gas), and also used in the manufacture of hydrochloric acid (by burning with chlorine).

4. Rocket and fuel applications: liquid hydrogen, burnt with liquid oxygen, is used as a high-energy rocket fuel; hydrogen is also explored as a clean-burning fuel for internal combustion and fuel-cell vehicles.

5. Oxy-hydrogen flame: burning hydrogen in oxygen produces a very high-temperature flame used for welding and cutting metals.

6. Reducing agent: hydrogen gas is used metallurgically to reduce metal oxides to the free metal (e.g. reduction of tungsten or molybdenum oxides in extracting these metals).

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