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Hydrogen

At room temperature and pressure, hydrogen gas exists as a diatomic molecule, H2

Occurrence

Hydrogen occurs in water, oils and natural gas

Preparation of hydrogen gas

1 Laboratory preparation of hydrogen

In the laboratory, hydrogen gas can be prepared by reacting:

  • a reactive metal with a dilute acid
  • a reactive metal with water

Reaction of reactive metal with a dilute acid

Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

hydrogen gas preparation

The gas is collected over water

Drying agent: Concentrated Sulphuric acid

Method of collection: Down ward displacement of air or upward delivery since it is less dense

2. Industrial preparation of hydrogen

On the scale, hydrogen gas is manufactured by the reaction of methane and steam

CH4(g) + H2O(g) → CO(g) + 3H2(g)

Conditions

Catalyst: Nickel metal

Temperature: 1000 degree Celsius

Pressure: 50 atmosphere

More steam is then added and the gases are passed over a catalyst iron (III) oxide to remove the carbon monoxide. Carbon dioxide is removed by dissolving it in water under pressure

3. Hydrogen can also be produced by cracking of alkanes

Test for hydrogen

Hydrogen gas burns with a pop sound when a burning splint is introduced to it

Physical properties of hydrogen

  1. It is colourless
  2. It is odorless
  3. It is less dense than air
  4. It has a boiling point of -253 degree Celsius
  5. It is not poisonous and does not support life

Chemical properties of hydrogen

  1. It has no effect on litmus paper
  2. It burns in oxygen with a blue flame producing a pop sound
  3. It is a reducing agent. It reduces the oxides of metals below it in the reactivity series. When hydrogen is passed over black copper (II) oxide in the apparatus above, the black powder turns pink
  4. When hydrogen is passed over black copper (II) oxide in the apparatus above, the black powder turns pink. A mixture of hydrogen and chlorine is explosive in sun light

Uses of hydrogen gas

  1. It is used in the manufacture of ammonia in haber process
  2. It is used in the manufacture of margarine from vegetable oil in the process called catalytic hydrogenation
  3. Liquid hydrogen is used as a fuel in rockets
  4. It is used as a reducing agent