Question

In the preparation of $H_{2}S{O}_4$ by contact process, why is $S{O}_3$ not absorbed directly in water to form $H_{2}S{O}_4$?

Answer 1

Contact process

* Contact process is an industrial process of producing sulphuric acid.

* $S{O}_3$ obtained in this process is added to sulphuric acid to form oleum $\left(H_2{S}_2{O}_7\right)$

$S{O}_3\left(g\right)+H_{2}S{O}_4\left(l\right)\to H_2{S}_2{O}_7\left(l\right)$

* $S{O}_3$ is not directly dissolved in water to form sulphuric acid because it resluts in the formation of dense fog of sulphuric acid which is difficult to condense.

* Also, addition of sulphur trioxide to water is highly exothermic in nature, which also increases the challenges in handling the process.