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 BaCl_(2) and gives a red colour compound with alizarin. Identify A and B.

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

1.	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 BaCl_(2) and gives a red colour compound with alizarin. Identify A and B.
Answer» SOLUTION :(i) A double salt which contains fourth period alkali metal (A) is potash a alum `"K"_(2)"SO"_(4)cdot"Al"_(2)(SO_(4))_(3)cdot24"H"_(2)O` (ii) On heating potash alum (A) 500 K give anhydrous potash alum (or) burnt alum (B). `underset((A))underset(("Potash alum"))("K"_(2)"SO"_(4)cdotAl_(2)(SO_(4))_(3)cdot24"H"_(2)"O")overset(500K)to underset((B))underset(("Burnt alum"))("K"_(2)"SO"_(4)cdotAl_(2))(SO_(4))_(3)+24H_(2)"O"` (iii) Aqueous solution of burnt alum, has sulphates ion, potassium ion and aluminium ion. SULPHATE ion reacts with `BaCl_(2)` to form white precipitate of Barium Sulphate: `(SO_(4))^(2-)+BaCl_(2)to BaSO_(4)+2CL^(-)` Aluminium ion reacts with ALIZARIN solution to give a red colour compound.