Calculate the concentration of sulfate ions in a 0.905 M aluminum sulfate solution?

Question

Please help! The only help the instructions offer is to try writing out the equation for the ionization of aluminum sulfate. It doesn't help. I've tried everything I could think of involving the molar ratio of aluminum sulfate. I can't begin solve this with so little info.

Answer 1

Aluminum sulfate combines Al3+ and SO4 2-

So aluminum sulfate is Al2(SO4)3 (charge balance)

So 0.905 M aluminum sulfate is 1.810 M in Al and ...