this is how you do it
For something monoprotic:
HCl\to H^+ +Cl^{-}
$mole ratio$
1: 1: 1
For something Diprotic as H_2 SO_4
$mole ratio$
H_2 SO_4 \to 2H^+ +SO_4 ^{-2}
1: 2: 1
Hence, with something triprotic, you divide the moles of the triprotic acid by 3 to get the moles of the H ions. so that...