The method of preparation of the colloidal sol of AI(OH)3 is exactly similar to that of Fe(OH)3 sol except that instead of FeCl3, 2% AlCl3 solution is used.

The hydrolysis takes place as follows:

AlCl3 + 3H2O → Al(OH)3 + 3HCl

The HCl produced is removed by dialysis. The sol formed in this case is colourless.