Question

On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, white precipitate is obtained.

(a) Write a balanced chemical equation of the reaction involved.

(b) What other name can be given to this precipitation reaction?

(c) On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why?

Answer 1

a) Balanced chemical equation:

$\begin{array}{ccccccc}{\text{Na}}_2{\text{SO}}_3\text{(aq)}& +& {\text{BaCl}}_2\text{(aq)}& \to & {\text{BaSO}}_3\text{(s)}& +& 2\text{NaCl (aq)}\\ \text{Sodium}& & \text{Barium}& & \text{Barium}& & \text{Sodium}\\ \text{sulphite}& & \text{chloride}& & \text{sulphite}& & \text{chloride}\end{array}$

(b) This reaction is also known as double displacement reaction.

(c) ${\text{BaSO}}_3$ when treated with dilute $\text{HCl}$ forms barium chloride and liberates sulphur dioxide gas which has a characteristic odour of burning sulphur. The reaction occurs as follows:

${\text{BaSO}}_3\text{(s)}+2\text{HCl (aq)}\to {\text{BaCl}}_2\text{(aq)}+{\text{H}}_2\text{O(l)}+{\text{SO}}_2\text{(g)}$
(White)

Since, ${\text{BaCl}}_2$ is water- soluble, the white precipitate disappears.