Question

(a) Name the process by which sodium hydroxide is prepared from sodium chloride? Why it is called so process and write down the balanced chemical equation.

(b) What will be the pH of the following salts?

1. Salt made of strong acid and strong base.
2. Salt made of strong acid and weak base.

Answer 1

Part -(a)

Chlor-alkali process is used to prepare sodium hydroxide using sodium chloride.

1. When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide.
2. The process is called the chlor-alkali process because of the products formed- chlor for chlorine and alkali for sodium hydroxide. The balanced chemical equation is given below:

$\underset{\left(\mathrm{sodium}\mathrm{chloride}\right)}{2\mathrm{NaCl}\left(\mathrm{aq}\right)}+\underset{\left(\mathrm{water}\right)}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{(\mathrm{sodium}\mathrm{hydroxide})}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}+\underset{\left(\mathrm{Chlorine}\right)}{{\mathrm{Cl}}_2\left(\mathrm{g}\right)}+\underset{\left(\mathrm{Hydrogen}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

Part -(b)

Be pH scale is a scale for measuring acids and bases. This scale ranges from $0-14$. Litmus paper is used as an indicator of pH. Litmus paper is used to tell whether a substance is an acid or a base.

The pH of the following salts:

1. pH of salt made of strong acid and strong base is always 7.
2. pH of salt made of strong acid and weak base is less than 7.