Sulphur(IV)oxide can be used as a

Analysis

The question asks for a common industrial or laboratory application of Sulphur(IV) oxide ($SO_2$). We need to evaluate its chemical properties to determine which of the provided options is a correct use.

Concept Explanation

Sulphur(IV) oxide ($SO_2$) is a gas with several distinct chemical properties:

1. Reducing Agent: It is a strong reducing agent.
2. Bleaching Agent: It bleaches colored materials by reduction (this is temporary, unlike chlorine which bleaches by oxidation).
3. Acidic Oxide: It reacts with water to form trioxosulphuric(IV) acid ($H_2SO_3$).
4. Physical Property: It can be easily liquefied under pressure, which makes it useful in specific industrial applications.

Let’s evaluate the options:

• A (Coating agent): $SO_2$ is not used for coating surfaces.
• B (Dehydrating agent): Concentrated tetraoxosulphate(VI) acid ($H_2SO_4$) is a powerful dehydrating agent, but $SO_2$ is not.
• C (Refrigerant): Because $SO_2$ has a relatively high boiling point and can be easily liquefied under moderate pressure, it was historically used as a refrigerant in industrial cooling systems.
• D (Drying agent): $SO_2$ is acidic and would react with basic drying agents; it is not used to dry gases.

Step-by-Step Solution

1. Identify the chemical nature: $SO_2$ is a gas that liquefies at approximately -10°C at atmospheric pressure.
2. Evaluate industrial utility: In the early days of refrigeration, $SO_2$ was widely used because it is easy to compress into a liquid and absorbs heat when it evaporates.
3. Compare with other options: • $H_2SO_4$ is the dehydrating agent (Option B is incorrect). • $P_2O_5$ or anhydrous $CaCl_2$ are common drying agents (Option D is incorrect). • $SO_2$ fits the criteria for a refrigerant.

Conclusion

Based on the chemical properties of Sulphur(IV) oxide, it is recognized for its use as a refrigerant in industrial applications.

Exam Tip

When you see questions about $SO_2$, remember the "Bleaching by Reduction" rule. If a question asks what gas bleaches flowers but the color returns when exposed to air, it is definitely $SO_2$. Also, don't confuse $SO_2$ (a refrigerant) with $H_2SO_4$ (a dehydrating agent)—JAMB loves to test if you know the difference between these two sulphur compounds!