Phosphoric acid is a tribasic acid. What is the mass of Ba(OH)2\text{Ba(OH)}_2Ba(OH)2 that completely neutralises 250 cm3 of 0.120 mol dm-3 phosphoric acid?
3.43 g3.43\text{ g}3.43 g
5.14 g5.14\text{ g}5.14 g
7.71 g7.71\text{ g}7.71 g
15.42 g15.42\text{ g}15.42 g