Which of these is the key compound for the laboratory preparation of sulphuric acid?
Sulphur dioxide
Sulphur dioxide is the key compound for the laboratory preparation of sulphuric acid.
2SO2(g)+O2(g)→2SO3
SO3+H2O→H2SO4
Nitric acid is another compound used for the laboratory preparation of sulphuric acid. S+6HNO3→6NO2+2H2O+H2SO4
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.