JAMB - Chemistry (2019 - No. 16)
SO\(_3\) is not directly dissolved in water in the industrial preparation of H\(_2\)SO\(_4\) by the contact process because
SO\(_3\) is an acidic gas
Acid is usually added to water and not water to acid
The reaction between SO\(_3\) and water is violently exothermic
SO\(_3\) does not dissolve readily in water
Explanation
Sulphur trioxide (SO\(_3\)) is not directly dissolved in water to produce sulphuric acid (H\(_2\)SO\(_4\)) because the reaction is highly exothermic and produces a fine mist of sulphuric acid, which is difficult to control and condense. Instead, SO\(_3\) is absorbed in concentrated sulphuric acid (oleum) to form oleum, which is then diluted with water to produce the desired sulphuric acid concentration.