You need to calculate the correct volume of 3 M sulfuric acid which will need to be added to neutralize the base. Consider that there are two sources of OH-in this procedure. Also, an excess of 3 mL will need to be added to your calculated value in order to suppress the hydrolysis of Al 3+.
Procedure:
Weigh out on a platform balance 4.0 g of the Al(OH)3-Fe2o3 mixture (75% al(OH)3 by weight). Place in a 250 mL beaker, and add 15 mL of water followed by 25 mL of 2 M KOH. Heat nearly to boiling, while stirring constantly, keeping the mixture hot for 5 min so that the Al (OH)3 dissolves.