Question

Why is sulfur trioxide not dissolved in water and but treated with existing sulfuric acid?

(a) It is not economically feasible

(b) Manufacturing plants cannot withstand the great pressure of dissolving sulfur trioxide in water

(c) Sulfur trioxide just hydrates on dissolving with no chemical bonds form

(d) The heat of dissolution is very high and potentially dangerous

This question was posed to me in an internship interview.

I want to ask this question from P-Block Elements topic in division P-Block Elements of Chemistry – Class 12

Answer 1

The correct answer is (d) The heat of dissolution is very high and potentially dangerous

The explanation is: The reaction between sulfur trioxide and water is highly exothermic and releases great amount of energy that no plant, currently, has the ability to withstand. Due to potential risks of explosion and fire hazard, sulfur trioxide is not dissolved in water but treated with sulfuric acid to produce oleum. This can be diluted to desired concentrations.