Question

Which of these is the key compound used in the Contact process?

• A. Sulphur dioxide
• B. Sulphur trioxide
• C. Nitric oxide
• D. Sulphur monoxide

Answer 1

The correct option is A

Sulphur dioxide

Sulphur dioxide is the key compound for the laboratory preparation of sulphuric acid.

$2S{O}_2\left(g\right)+O_2\left(g\right)\to 2S{O}_3$

$S{O}_3+H_{2}O\to H_{2}S{O}_4$

Nitric acid is another compound used for the laboratory preparation of sulphuric acid.

$S+6HN{O}_3\to 6N{O}_2+2H_{2}O+H_{2}S{O}_4$

Sulphur dioxide can directly be oxidized to sulphuric acid using nitric acid. So getting to sulphur trioxide is not a mandatory step in laboratory synthesis. Converting sulphur or pyrites into sulphur trioxide is not direct/easy.