SO3 is not directly dissolved in water in the industrial preparation of H2SO4 by the contact process because
- A. SO3 is an acidic gas
- B. Acid is usually added to water and not water to acid
- C. The reaction between SO3 and water is violently exothermic
- D. SO3 does not dissolve readily in water
The direct reaction between water and sulfur trioxide is extremely violent and exothermic. This is why instead; sulfur trioxide is usually dissolved in concentrated sulfuric acid to form oleum (H2S2O7). This oleum is then dissolved in water to form concentrated sulfuric acid.
Now for the right answer to the above question:
- Option A is incorrect. being an acidic gas not good enough reason to avoid direct dissolution, there are other acidic gasses that can be comfortably dissolved in water to form acids.
- Option B is incorrect. water is often added to acid to dilute it. Besides, this option is not good enough a reason as requested by the question.
- C is correct.
- D is not the correct answer. Sulfur trioxide does dissolve in water, but of course, violently.
You may please note these/this:
- Instead of dissolving directly in water, sulfur trioxide is often dissolved in concentrated sulfuric acid to form oleum and then water finally added to this oleum to give more conc sulfuric acid.
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/culled from 2019 JAMB-UTME Chemistry question 16/