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Difficulty: MediumTetraoxosulfate(VI) Acid: Contact Process and Properties

In the industrial manufacture of tetraoxosulfate(VI) acid via the Contact Process, sulfur(VI) oxide (SO3SO_3) gas is absorbed into concentrated tetraoxosulfate(VI) acid to form oleum (H2S2O7H_2S_2O_7) rather than being dissolved directly in water. What is the primary chemical reason for avoiding direct dissolution in water?

  1. Direct reaction with water is violently exothermic and creates a dense mist of acid droplets that is extremely difficult to condense.Answer
  2. B
    Water oxidizes sulfur(VI) oxide into trioxosulfate(IV) acid instead of tetraoxosulfate(VI) acid.
  3. C
    Direct addition of water shifts the dynamic equilibrium position backward, significantly reducing the yield of product.
  4. D
    Water fails to react stoichiometrically with sulfur(VI) oxide gas at standard molar volume conditions.

Answer

Direct reaction with water is violently exothermic and creates a dense mist of acid droplets that is extremely difficult to condense.
Direct addition of sulfur(VI) oxide gas to water liberates excessive thermal energy, rapidly boiling the water and creating a fog or mist of fine tetraoxosulfate(VI) acid droplets that cannot be collected easily in industrial towers. Absorbing SO3SO_3 in 98% H2SO4H_2SO_4 forms oleum (H2S2O7H_2S_2O_7) controlledly without mist generation.

Step-by-Step Solution

1
Analyze the chemical interaction between SO3SO_3 and H2OH_2O
The reaction SO3(g)+H2O(l)→H2SO4(aq)SO_3(g) + H_2O(l) \rightarrow H_2SO_4(aq) is extremely exothermic.
Large enthalpy of hydration releases intense localized thermal energy.
2
Identify the physical consequence of direct hydration
The heat vaporizes surrounding water and acid, forming a micro-droplet acid aerosol/mist.
Fine mist droplets cannot easily settle or condense using conventional absorption towers.
3
Evaluate the industrial solution in the Contact Process
SO3SO_3 is absorbed smoothly into 98% H2SO4H_2SO_4 to form oleum (H2S2O7H_2S_2O_7), which is subsequently diluted safely with water.
Absorption in concentrated acid avoids mist formation while maintaining high efficiency.

Key Concept

Contact Process SO3SO_3 Absorption Mechanics
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Topics

Tetraoxosulfate(VI) Acid: Contact Process and Properties

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