A contact sulphuric acid plant burns pure sulphur with air. The products of combustion pass to a converter where some of the SO₂ is converted to SO₃ at a fast rate owing to the high temperature of the gas. However, because of an unfavourable equilibrium in high temperatures, the gas is cooled and sent to a final converter where the oxidation can be carried out further. The lower temperatures favours a greater conversion of SO₂ and SO₃. The gas from the first converter was found to contain 4.5 vol% SO₂. The gas from the final converter contained 0.1% SO₂ and 8% O₂.

(a) What percentage of the total SO₂ was converted to SO₃ in the first and second converter?

(b) What was the excess air used to burn the sulphur?