Question

(a) What happens when a concentrated solution of sodium chloride (brine) is electrolysed? Write the equation of the reaction involved.
(b) Why is the electrolysis of a concentrated solution of sodium chloride known as chlor-alkali process?
(c) Name three products of the chlor-alkali process. State two uses of each of these products.

Answer 1

(a) When electricity is passed through a concentrated solution of sodium chloride called brine, the solution decomposes to form sodium hydroxide, chlorine and hydrogen.

$2\mathrm{NaCl}\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\underset{\mathrm{electrolysis}}{\overset{\mathrm{electrolyte}}{\to }}2\mathrm{NaOH}\left(\mathrm{aq}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

(b) The process of electrolysis of sodium chloride solution is called the chlor-alkali process because 'chlor' (chlorine) and alkali (sodium hydroxide, NaOH) are formed as products.

(c) The three main products of the chlor-alkali process are H₂, Cl₂ and NaOH.

Uses of sodium hydroxide:

(i) It is used for making soaps and detergents.
(ii) It is used for making synthetic textile fibre (such as rayon).

Uses of chlorine:

(i) It is used in the production of bleaching powder.
(ii) It is used to sterilise drinking water supply and the water in swimming pools, because it is a disinfectant.

Uses of hydrogen:

(i) It is used in the hydrogenation of oils to obtain solid fats called vegetable ghee.
(ii) Liquid hydrogen is used as a fuel for rockets.