ALPHA-AL2O3 + GAMMA-ALUMINA

For a good quality cement,the ratio of silica ( SiO_2 ) to alumina ( Al_2O_3 ) is between :-

Explain the following (i) Excess of carbon is added to zinc metallurgy. (ii) In the elctrolysis of alumina, cryolite is added to alumina. (iii) Coke does not cause reduction of Al_(2)O_(3) . (iv) Gold is soluble in aquaregia, silver is not.

Calculate Delta H for the reaction Al + Cr_2O_3 rarr Cr +Al_2O_3 When enthalpy of formation of Al_2O_3 and Cr_2O_3 , are -1596 kJ and -1133 kJ respectively.

The Gibbs energy for the decomposition of Al_2 O_3 at 2/3 Al_2O_3 rarr 4/3 Al = O_2 Delta_r G = + 966 k J "mol"^(-1) The potential differnce needed for electrolytic reduction of Al_2 O_3 at 500^@C is at least.

Aluminium is extracted from alumina ( Al_2O_3 ) by electrolysis.

Anhydrous alumina (Al_(2)O_(3)) is known as