Question

What mass (nearest integer) of phosphoric acid, $H_{3}P{O}_4$ is required to prepare $550$ mL of $0.40N$ solution? (assuming complete neutralisation of acid)

Answer 1

The complete neutralization of $H_{3}P{O}_4$ means it will act as a tribasic acid.

$0.40N{H}_{3}P{O}_4$ corresponds to $\frac{0.40}{3}M{H}_{3}P{O}_4$.

$1L$ of solution will contain $\frac{0.40}{3}$ moles.
$550$ mL of solution will contain $\frac{0.40\times 550}{3\times 1000}$ moles.

This corresponds to $H_{3}P{O}_4=\frac{0.40\times 550\times 98}{3\times 1000}=7.187$ g.

The nearest integer is $7$.