Italian IMAT 2019 Q 47

Tooth enamel consists mostly of hydroxyapatite, the formula unit of which is
Ca5 (PO4) 3 (OH). In an acid medium for sulfuric acid, it can be decomposed according to thefollowing reaction:
Ca5 (PO4) 3 (OH) + 4H + → 5Ca2 + + 3HPO42− + H2O
How many moles of H2SO4 are needed to produce 0.3 moles of HPO4 ions2- ?
A) 0.4
B) 0.3
C) 0.1
D) 0.2
E) 0.5

Hi everyone!
Answer is D), what are the steps here i’m a bit confused

1 Like

Hi! We can use molar ratio. so 4 H+ ions from sulphuric acid give 3 HPO4 ions.
4/3 = x/0.3
0.4 mols of H+. Now we know sulphuric acid is diprotic so we divide that by 2 = 0.2 mol. Hope this helps!