Answer to Question #239570 in General Chemistry for nugget

Question

Al3 O3 + Na OH form Al2NaO2 (for this I understand but why one of the O from Al3O3 did not match with OH to form HO2 instead it form H2O)and water? I understand that from the question that water is formed but how do I explain that one of the O from Al3O3 goes with OH form one H(hydrogen) and 2 O(oxygen), please enlighten.

If O with 2- in valency electron is criss-cross with H is 1+ in valency electron to get H2O why then Al3 that has 3+ in valency electron was not criss-cross with Na which has 1+ in valency electron in the equation? I am lost. Please help.

Answer 1

Simple non-ignited Al2O3 or Al(OH)3 is soluble in common acids or aqueous NaOH forming Al+3 salt (in case of acid) or NaAlO2 (with aq. NaOH). But ignited alumina is insoluble in common acids. However ignited Al2O3 thoug insoluble in conc. acids like HCl or HNO3 is soluble in NaOH on heating. In fact ignited alumina on fusion with NaOH forms NaAlO2 and H2O (2NaOH + Al2O3 = 2NaAlO2 + H2O). The mixture when treated with water forms a clear solution of Sodium aluminate