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?