Question

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

\[\ce{P + 5HNO3 -> H3PO4 + H2O + 5NO2}\]

1. What mass of phosphoric acid can be prepared from 6.2 g of phosphorus?
2. What mass of nitric acid will be consumed at the same time?
3. What will be the volume of steam at the same time measured at 760 mm Hg pressure and 373°C?
   (H = 1; N = 14; O = 16; P = 31∴ )

Answer 1

\[\ce{\underset{31 g}{P} + 5HNO3 -> \underset{(98 g)}{H3PO4} + H2O + 5NO2}\]

i. 31 g of P = 1 mole

∴ 9.3 g of P = `1/31 xx 9.3`

= 0.3 moles

Hence, 0.3 moles of phosphorus were taken for the reaction.

ii. 31 g of P forms 98 g of phosphoric acid.

∴ 9.3 g of P = `98/31 xx 9.3`

= 29.4 g

Hence, 29.4 g of phosphoric acid is formed.

iii. 31 g of P produces 5 vol = 5 × 22.4 lit.

∴ 9.3 g will produce = `(5 xx 22.4)/31`

= 33.6 lit.