Question

216. Sodium chloride was used as an important symbol in our freedom struggle. Mahatma Gandhi and his followers did Dandi march in order to stop the British government from increasing the price of common salt used daily by Indian people.

(e) How is sodium hydroxide prepared from common salt?

Answer 1

• Sodium hydroxide can be prepared by the electrolysis of an aqueous solution of Sodium chloride.
• When electricity is transmitted through an aqueous Sodium chloride solution (called brine), Sodium hydroxide or Caustic Soda $\left(\mathrm{NaOH}\right)$is formed.
• Sodium hydroxide is deposited at the cathode during electrolysis, while water is converted to hydroxide ions and hydrogen gas.
• Due to the formation of Chlorine and alkali (Sodium hydroxide), this process is called the chloralkali process.
• The chemical equation for the reaction is :

$\underset{\mathrm{Sodium}\mathrm{Chloride}}{2\mathrm{NaCl}\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Sodium}\mathrm{hydroxide}}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}+\underset{\mathrm{Chlorine}\mathrm{gas}}{{\mathrm{Cl}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Hydrogen}\mathrm{gas}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$