When electrolysis of water is done then :
(a) Identify the gases evolved at cathode and anode. (Write equations also)
(b) Why is amount of gas evolved collected in one of the testtube doubles the amount in the other? Name this gas. 

Asked by pdcavita | 21st Dec, 2017, 06:46: PM

Expert Answer:

 Electrolysis of Acidified Water

Electrolyte: Acidified water


Anode: Platinum

Cathode: Platinum

Ionisation of acidified water: H2O  → H+ + OH

                                              H2SO4  → 2H+ + SO42–

Ions present: H+, SO42–, OH

Electrode reactions: 

Reaction at the cathode: H+ + e → H

                                         H + H H2 (hydrogen molecule)

Reaction at the anode: OH − e  → OH × 4

OH– ion discharge in preference to SO42–

                  4OH → 2H2O + O2 (oxygen molecule) 

At the cathode, Hydrogen gas is evolved and at the anode, oxygen gas is liberated.


The water molecule has two atoms of hydrogen and one atom of oxygen, that means in the no. of hydrogens are double than that of oxygen,

hence the amount of hydrogen gas evolved collected in one of the test tubes doubles the amount in the other gas i.e., oxygen.

Answered by Ramandeep | 22nd Dec, 2017, 10:25: AM