Question

During the electrolysis of acidified water, where would oxygen and hydrogen gas be liberated?

• A. Oxygen is liberated at anode, hydrogen is liberated at cathode
• B. Oxygen is liberated at cathode, hydrogen is liberated at anode
• C. Both are liberated at cathode
• D. Both are liberated at anode

Answer 1

The correct option is A Oxygen is liberated at anode, hydrogen is liberated at cathode

During the electrolysis of acidified water, $H^{+}$ ions are obtained when sulphuric acid ionizes. The $H^{+}$ ions combines with water and forms $H_3{O}^{+}$ ions. Following reaction takes place between the water and sulphuric acid: $H_{2}S{O}_4\left(aq\right)+2H_{2}O\left(l\right)\to 2H_3{O}^{+}\left(aq\right)+S{O}_4^{2-}\left(aq\right)$

Therefore, the reaction which occurs at cathode is:
$2H_3{O}^{+}\left(aq\right)+2e^{-}\to H_2\left(g\right)+2H_{2}O\left(l\right)$

Though the ion which moves towards anode is $S{O}_4^{2-}$, the actual reaction which occurs at anode is:
$2H_{2}O\left(l\right)\to O_2\left(g\right)+4H^{+}\left(aq\right)+4e^{-}$

This is because water has a high tendency to get oxidised than $S{O}_4^{2-}$.

Hence, oxygen gas gets liberated at anode and hydrogen gas gets liberated at cathode.