Question

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

1. Write a balanced chemical equation of the reactions involved.
2. What other name can be given to this precipitation reaction?
3. On adding dilute hydrochloric acid to the reaction mixture, white precipitation disappears, why?

Answer 1

Step 1: Balanced chemical equation of the reactions

• On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, barium sulphite is obtained which is a white colour precipitate.
• Barium Chloride + Sodium sulphite = Barium sulphite + Sodium chloride

${\mathrm{BaCl}}_2\left(\mathrm{aq}\right)+{\mathrm{Na}}_2{\mathrm{SO}}_3\left(\mathrm{aq}\right)\to {\mathrm{BaSO}}_3+2\mathrm{NaCl}$

Step2: Another name for this reaction

• The precipitation reaction is a double displacement.

Step 3: The reason for white precipitation disappears while adding dilute hydrochloric acid to the reaction mixture

• When we add dilute HCl to this reaction mixture barium chloride, sulphur dioxide, and water are formed.
• Barium chloride is a soluble substance that will make the white precipitate disappear.
• Barium sulphite+ dil.Hydrochloric acid = Barium chloride+ Sulphur dioxide+ water

${\mathrm{BaSO}}_3\left(\mathrm{s}\right)+\mathrm{HCl}\left(\mathrm{l}\right)\to {\mathrm{BaCl}}_3\left(\mathrm{aq}\right)+{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$