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.

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Solution

## (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. ${\mathrm{FeSO}}_{4}+{\mathrm{BaCl}}_{2}\to {\mathrm{BaSO}}_{4}+{\mathrm{FeCl}}_{2}$

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