Q. Show the properties of Aluminium Oxide ?
Aluminium oxide, Al203 is a highly ionic compound of aluminium. It is also known as alumina. As you have studied earlier, it occurs in nature not only as bauxite and colourless corundum, but also as coloured gem stones like ruby, emerald, sapphire and topaz, etc. Colours of these gem stones are due to the presence of transition metal ions. Anhydrous aluminium oxide can exist in two forms both of which are white. These are a-Al203 and 7-AI2O3. The 7-AI2O3 is formed by dehydrating AI (OH) 3 below 750 K:
2AI (OH)3--------------------------------------> 7-Al2O3 + 3H20
The 7-Al203 is quite reactive. It dissolves readily in both acids and bases. If the 7-AI2O3 is heated to 1500 K, it changes to the a-AI2O3, which is called corundum. Corundum has a very high melting point (about 2328 K). It is very hard and inert,-especially towards acids.