(I) Alumina is nature occurs as a colourless mineral corundum. Being amphoteric it reacts with acids as well as alkalis. It is used to prepare anhydrous aluminium chloride by passing chlorine gas over heated mixture of alumina and carbon. Write the balanced chemical equation for the same.
(II) Double salts of the type M2SO4, M’2 (SO4)3, 24H2O are called alums.Here M is univalent ion such as Na+, K+ etc. Whereas M’ is a trivalent ion like Al3+ , Fe3+ etc. Potash alum [K2SO4, Al2(SO4)3 . 24H2O] the common alum is manufactured from alum shale which contains iron disulphide and aluminium silicate (Al2O3. xSiO2) and that is roasted in excess air to yield aluminium sulphate and ferrous sulphate. Ferrous sulphate is removed by fractional crystallisation and calculated quantity of K2SO4 is added to the mother liquor which is concentrated to give crystals of alum. Write balanced chemical equation for roasting of alum shale.
