Discovered by Cavendish and named by Lavoisier. Hydrogen means “water provider” (former). Hydrogen is the first element of the periodic table. It has the symbol H and exists as a diatomic element (H₂).

Occurrence

Hydrogen occurs in water, oil, natural gas and in all living things. Hydrogen gas does not occur as single atoms but as a molecule (H₂).

Physical Properties of H₂

• It is a colorless and odorless gas.
• It is lighter than air and it is the lightest substance.
• It is not very soluble in water.
• It is poisonous but does not support life.
• It is neutral to litmus.
• It has a very low boiling point (-25°C).
• It is inflammable. I.e.: It quickly explodes.

Chemical Properties of H₂

• It burns with a blue flame producing water.

2H2 (g)+O2 (g)→2H2O(g)

The water can be tested using white anhydrous copper II sulphate which turns blue.

• Hydrogen is a reducing agent. It reduces the oxide of metals that are found below it in the reactivity series. Eg; PbO, CuO etc…

If the hydrogen is passed through heated black copper II oxide, it reduces it to reddish brown copper.

H2 (g)+CuO(s)→Cu(s)+H2O(g)

H2 (g)+PbO(s)→Pb(s)+H2O(g)

Laboratory Preparation of Hydrogen (H₂)

• Aim: It can be prepared in the laboratory by reacting granulated zinc with HCL.
• Requirements: Dilute HCL, zinc, thistle funnel water, delivery tube, flat bottomed flask, gas jar stand, trough and water.
• Procedure: It can be prepared in the laboratory by reacting granulated zinc with dilute HCL.

Zn(s)+2H(g)→Zn(aq)++H2 (g)

Zn(s)+2HCL(l)→ZnCl2 (aq)+H2 (g)

Dilute sulphuric acid can be used in the place of HCL.

Zn(s)+H2SO4(aq)→ZnSO4 (aq)+H2 (g)

If the gas is required dry, it can be passed over concentrated sulphuric acid and is collected by upward delivery because it is lighter than air.