The diagram shows the stages during the manufacture of sulphuric acid by the Contact Process.

1. aGive one source of sulphur. [1]
2. bWrite a balanced equation for the reversible reaction between sulphur dioxide and oxygen to form sulphur trioxide. [2]
3. cName the catalyst used in the Contact Process. [1]
4. dExplain why a temperature of 450 °C is preferred to higher temperatures like 1000 °C. [1]
5. eExplain why sulphur trioxide is not dissolved directly in water to make oleum. [1]

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