Concentrated nitric acid oxidises phosphorus to phosphoric acid according to the following equation:

P + 5HNO₃ ⟶ H₃PO₄ + 5NO₂ + H₂O

(a) What mass of phosphoric acid can be prepared from 3.1 g of phosphorus?

(b) What mass of nitric acid will be consumed at the same time?

$\begin{matrix} \text{P} & + & 5\text{HNO}$3 & \longrightarrow & \text{H}3\text{PO}4 & + & \text{H}2\text{O} & + & 5\text{NO}_2 \ 31 \text{ g} & & 5[(1)+14+3(16)] & & 3(1) + 31 \ & &= 5[63] & & + 4(16) \ & & = 315 g & & = 98 \text{ g} \ \end{matrix}

(a) 31 g of P forms 98 g of phosphoric acid

∴ 3.1 g will form $\dfrac{ 98}{31}$ x 3.1 = 9.8 g.

Hence, 9.8 g of phosphoric acid is formed

(b) 31 g of P consumes 315 g of nitric acid.

∴ 3.1 g will consume = $\dfrac{315}{31}$ x 3.1 = 31.5 g