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 names 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 

Na₂SO₃(aq) + BaCl₂(aq) → BaSO₃(s) + 2NaCl (aq)

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

(c) BaSO₃ is a salt of a weak acid (H₂SO₃), therefore dilute acid such as HCl decomposes barium sulphite to produce sulphur dioxide gas which has the smell of burning sulphur.

 BaSO₃ (s) + 2HCl (aq) → BaCl₂ + H₂O + SO₂ (g) White ppt.

 BaCl₂ is soluble in water, hence white precipitate disappears