Question

Choose the correct statement regarding electrolysis of acidified water from the options given below.

• A. Pure water ionises to a small extent.
• B. Hydrogen is obtained at the cathode.
• C. Oxygen is obtained at the anode.
• D. Water has a lesser tendency to get oxidized.

Answer 1

Answer: (A), (B), (C)

The correct options are
A

Pure water ionises to a small extent.

B

Hydrogen is obtained at the cathode.

C

Oxygen is obtained at the anode.

The number of ions is very less in pure water. So, it ionizes to a very small extent. A little of dilute sulphuric acid is mixed with water, which when ionizes gives

$H^{+}$ ions. These $H^{+}$ ions combine with water and form $H_3{O}^{+}$ ions.

$H_{2}S{O}_4\left(l\right)+H_{2}O\left(l\right)\to 2H_3{O}^{+}\left(aq\right)+S{O}_4^{2-}\left(aq\right)$

The reaction occurring at the cathode is:

$2H_3{O}^{+}\left(aq\right)+2e^{-}\to H_2\left(g\right)+2H_{2}O\left(l\right)$

The ions moving towards positive electrode is $S{O}_4^{2-}$. On comparing $S{O}_4^{2-}$ with water, water has a higher tendency to get oxidised.

The reaction occurring at the anode is:

$2H_{2}O\left(l\right)\to O_2\left(g\right)+4H^{+}\left(aq\right)+4e^{-}$

Hydrogen gas is obtained at the cathode and oxygen gas is obtained at the anode.