Answers section

Questions 5.2.1

How does the density of sulphur (IV) oxide compare with that of air? (S = 32; O =16; N = 14)
Draw a diagram of the set-up you would use to prepare a dry sample of sulphur (IV) oxide.
Explain the methods of drying and collecting the gas as represented in your set-up.
Write an equation for the reaction that takes place.
Explain why, although the burning of sulphur in air (or oxygen) produces sulphur (IV) oxide, it is not suitable for preparing the gas.

Answers to Questions 5.2.1

RMM of SO₂ = 32 + (16x2) = 64, which is greater than the average for air (28 to 32). So the gas is denser than air.
Drawing
The gas is dried using concentrated sulphuric acid because the two are acidic; so they do not react with each other. It is collected by downward delivery because it is denser than air.
Na₂SO₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + SO₂(g)
It is difficult to collect a pure or fairly pure sample of the gas in that arrangement. It is contaminated with unreacted air.