Hydrogen is the lightest and most abundant element in the universe. It plays a crucial role in the formation of stars through nuclear fusion. On Earth, hydrogen is commonly found in water molecules (H₂O) and various organic compounds

Hydrogen has a single electron in the outermost shell. Hence it is placed in group 1. However, the properties of hydrogen varies from those of other group 1 elements. Hydrogen can also fit into group 7 due to its need for one electron to complete duplet configuration.

Hydrogen is however placed in group 1 for convenience.

The following are chemical processes used in preparing hydrogen in the laboratory.

1. Action of dilute acid on zinc: The action of diute acid like hydrochloric acid or tetraoxosulphate (VI) acid on zinc granules leads to the liberation of hydrogen gas.

   The gas is collected over water in a gas jar and can be dried using fused calcium chloride or conc. H₂SO₄ and then collected by downward displacement of air (Lighter than air).

   $$ Zn + HCl \rightarrow ZnCl_2 + H_2 $$ $$ Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2 $$
   Note: Trioxonitrate (V) acid will not liberate hydrogen with zinc because of its strong oxidizing nature. It will oxidize any hydrogen to water.

2. Action of cold water on active metals : Sodium and potassium reacts explosively with cold water, liberating hydrogen gas. This reaction is very vigorous and spontaneous.
$$ 2Na + 2H_2O \rightarrow 2NaOH + H_2 $$ $$ 2K + 2H_2O \rightarrow 2KOH + H_2 $$

3. Action of steam on iron: Iron reacts with steam at red heat to liberate hydrogen gas. A black residue of tri-iron tetraoxide is formed in the test tube. $$ 3Fe + 4H_2O \rightleftharpoons Fe_3O_4 + 4H_2 $$

1. From water gas: The industrial process of producing hydrogen from water gas is called Bosch process. Hydrogen is prepared on a large scale using this method.
   
   

   The process involves the passing of steam over red hot coke in a furnace at about 1100°C, water gas is formed (a mixture of carbon (II) oxide and hydrogen gas).

   $$ C + H_2O \rightarrow CO + H_2 $$

   Excess steam is passed into the water gas in the presence of iron (III) oxide or chromium (II) oxide as catalyst at 450°C. The CO is converted to CO_2 producing more hydrogen.

   $$ CO + H_2 + H_2O \rightleftharpoons CO_2 + 2H_2 $$ The carbon (IV) oxide formed is removed by passing the mixture through caustic alkali $$ NaOH + CO_2 \rightarrow Na_2CO_3 + H_2O $$ Any carbon (II) oxide is absorbed by using ammoniacal solution of copper (I) ethanoate.

2. From hydrocarbon (Methane) : Methane reacts with steam in the presence of nickel as catalyst at 800°C and 30 atm to produce a mixture of carbon (II) oxide and hydrogen called synthetic gas. $$ CH_4 + H_2O \rightarrow CO + 3H_2 $$

   The synthetic gas is dissolved in excess steam in the presence of iron (III) oxide as catalyst. The corresponding carbon (II) oxide formed is converted to carbon (IV) oxide which is absorbed by caustic alkali

   $$ CO + 3H_2 + H_2O \rightarrow CO_2 + 4H_2 $$
3. By electrolytic method: Hydrogen can be produced by electrolysis, a process that involves the decomposition of water into hydrogen and oxygen using an electric current. It is obtained as a bye-product in the electrolysis of brine.