I think it's ionically bonded, Al has a 3+ charge, SO4 has a 2- charge, we need the charge to add up to 0, so 2 Al gives 2x3=6 and 3SO4 gives 3x-2=-6, giving an overall charge of 0. Now that we have Al2(SO4)3, we know we have (SO4)3 on the right hand side, so we need 3 SO4 on the left, so we get 3H2SO4 on the left, similarly it's Al2 on the right, so we need 2Al on the left. Finally we have 3H2SO4 on the left, so we need 3H2 on the right.
Hey there! Aluminium Sulphate is an ionic compound. The charge on an Aluminium ion is +3, and the Sulphate ion is S042-. You have to make sure that each component's total charge adds to 0. Therefore, the negative ion needs to have an overall of -6 and the positive as +6 as they cancel out.
Al+3 - you need 2 of these
SO42-- you need 3 of these.