Question

Which one of the following statements is correct for electrolysis of brine solution?

• A. $OH ^{-}$is formed at cathode
• B. $Cl _2$ is formed at cathode
• C. $O _2$ is formed at cathode
• D. $H _2$ is formed at anode

Hint:

In the electrolysis of brine, chloride ions are oxidized at the anode to produce chlorine gas, and water molecules are reduced at the cathode to produce hydrogen gas and hydroxide ions.

Answer 1

The Correct Option is A

The electrolysis of brine (aqueous sodium chloride) produces several chemical species at the anode and cathode. Let's analyze what happens at each electrode:

1. Cathode Reaction: At the cathode, reduction occurs. In an aqueous solution of brine, water is reduced rather than sodium ions because water has a less negative electrode potential. The reaction is: \(2H_2O + 2e^- \rightarrow H_2 + 2OH^−\) 
   The product at the cathode is hydrogen gas (\(H_2\)) and hydroxide ions (\(OH^−\)).
2. Anode Reaction: At the anode, oxidation occurs. Chloride ions are oxidized to chlorine gas since they have a more favorable electrode potential compared to water. The reaction is: \(2Cl^− \rightarrow Cl_2 + 2e^−\) 
   The product at the anode is chlorine gas (\(Cl_2\)).

With this understanding, let's evaluate the given options:

• \(OH ^−\) is formed at cathode - This statement is correct since hydroxide ions are indeed produced at the cathode.
• \(Cl _2\) is formed at cathode - This is incorrect, as chlorine gas is formed at the anode, not the cathode.
• \(O _2\) is formed at cathode - This is incorrect, as oxygen gas is not formed at either electrode in the electrolysis of brine.
• \(H _2\) is formed at anode - This is incorrect, as hydrogen gas is formed at the cathode, not the anode.

Conclusion: The correct statement is that \(OH^−\) is formed at the cathode.