How many moles of al2 (so4) 3 can form under these conditions?

A. Since you are starting with equal moles of the two reactants, you can see from the balanced equation that you need 3 moles of H2SO4 for every 2 moles of Al (OH) 3. So, H2SO4 is the limiting reactant.

B. 0.420 mol H2SO4 X (1 mol Al2 (SO4) 3 / 3 mol H2SO4) = 0.140 mol Al2 (SO4) 3

C. Moles of Al (OH) 3 used:

0.420 mol H2SO4 X (2 mol Al (OH) 3/3 mol H2SO4)

= 0.280 mol Al (OH) 3 used Moles remaining

= 0.420 - 0.280

= 0.140 mol Al (OH) 3 remaining.