Question

Identify the substances P, Q, and R in each case based on the information given below:
(i) The deliquescent salt P, turns yellow on dissolving in water, and gives a reddish brown precipitate with sodium hydroxide solution.
(ii) The white crystalline solid Q is soluble in water. It liberates a pungent smelling gas when heated with sodium hydroxide solution.
(iii) The pale green solid R turns reddish brown on heating. Its aqueous solution gives a white precipitate with barium chloride solution. The precipitate is insoluble in mineral acids.

Answer 1

(i) P is ferric chloride. It is a deliquescent salt that gives yellow solution when dissolved in water. On reaction with sodium hydroxide, it forms reddish-brown precipitate of ferric hydroxide.
${\mathrm{FeCl}}_3+3\mathrm{NaOH}\to \mathrm{Fe}{\left(\mathrm{OH}\right)}_3+3\mathrm{NaCl}$

(ii) Q is ammonium chloride. It is a white crystalline solid. It is soluble in water. When heated with sodium hydroxide, it liberates pungent-smelling ammonia gas.
${\mathrm{NH}}_4\mathrm{Cl}+\mathrm{NaOH}\to {\mathrm{NH}}_3+\mathrm{NaCl}+{\mathrm{H}}_2\mathrm{O}$

(iii) R is ferrous sulphate. On heating, it turns reddish brown, forming ferric oxide. Aqueous ferrous sulphate reacts with barium chloride to form a white precipitate of barium sulphate, which is insoluble in mineral acids.
${\mathrm{FeSO}}_4+{\mathrm{BaCl}}_2\to {\mathrm{BaSO}}_4+{\mathrm{FeCl}}_2$