Describe the manufacture of

Sulphuric acid is manufactured by the contact process. It involves the following steps:

Step (i):

Sulphur or sulphide ores are burnt in air to form SO2.

Step (ii):

By a reaction with oxygen, SO2 is converted into SO3 in the presence of V2O5 as a catalyst.

$2 \mathrm{SO}_{2(g)}+\mathrm{O}_{2(g)} \stackrel{\mathrm{v}_{3} \mathrm{O}_{3}}{\longrightarrow} 2 \mathrm{SO}_{3(g)}$

Step (iii):

SO3 produced is absorbed on H2SO4 to give H2S2O7 (oleum).

$\mathrm{SO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}$

This oleum is then diluted to obtain H2SO4 of the desired concentration.

In practice, the plant is operated at 2 bar (pressure) and 720 K (temperature). The sulphuric acid thus obtained is 96-98% pure.