Question

iN ELECTROLYSIS of water why is the volume of gas collected overnone electrode double that of gas collected over the other electrode

Answer 1

In electrolysis of pure water, reaction at anode

2H2O→ O₂ (g) + 4 H⁺ (aq) + 4e^−

At cathode,

2 H⁺ (aq) + 2e^− → H₂ (g)

Half reaction can be balanced using base. To add half reactions they must both be balanced with either acid or base. So,

At Anode, 4 OH^- (aq) → O₂ (g) + 2 H₂O (l) + 4 e^− (oxidation)

At Cathode, 2 H₂O (l) + 2e^− → H₂ (g) + 2 OH^-(aq) (Reduction)

Combining either half reaction pair yields the same overall decomposition of water into oxygen and hydrogen:

Overall reaction: 2 H₂O (l) → 2 H₂ (g) + O₂ (g)

The number of hydrogen molecules produced is thus twice the number of oxygen molecules.