Question

Give a reason to support that sulphuric acid is a dehydrating agent.

A double salt which contains fourth period alkali metal (A) on heating at 500K gives (B). Aqueous solution of (B) gives white precipitate with BaCl₂ and gives a red colour compound with alizarin. Identify A and B.

Answer 1

(i) A double salt which contains fourth period alkali metal (A) is potash alum

K₂SO₄Al₂(SO₄)₃ . 24H₂O

(ii) On heating potash alum (A) 500 K give anhydrous potash alum (or) burnt alum (B).

(iii) Aqueous solution of burnt alum, has sulphates ion, potassium ion and aluminium ion. 

Sulphate ion reacts with BaCl₂ to form white precipitate of Barium Sulphate: 

(SO₄)^2- + BaCl₂ → BaSO₄ + 2Cl^- 

Aluminium ion reacts with alizarin solution to give a red colour compound.