Question

Calculate the volume of air at STP, required to convert 300 mL of sulphur dioxide to sulphur trioxide. Air contains 21% of oxygen by volume.

Answer 1

Conversion of sulphur dioxide to sulphur trioxide follows the following balanced equation :
4SO₂ + 2O₂ → 4SO₃
According to Gay -lussac's law:
4 vol. 2 vol. 4 vol.
Volume of SO2 = 4 vol. =300 ml
Volume of 0 2 = 2 vol. =300 x 2 / 4 = 150 ml
Volume of oxygen required = 21 °/o = 150 ml
Volume of air required at STP = 100°/o = 100 x 150 / 21 = 714.28 ml
So, the volume of air at STP, required to convert300 ml of sulphur dioxide to
sulphur trioxide is 714.28 ml