Which of the following statements regarding conc. Sulphuric acid is not correct?

Options

A. It is reduced to SO_2 on reaction with Cu.
B. It is a strong dehydrating agent.
C. It can be used to manufacture more volatile acids from their corresponding salts.
D. The absorption of SO_2 is sulphuric acid produces oleum.

Answer

To determine which statement regarding concentrated sulfuric acid is not correct, let's analyze each statement one by one:

1. **Statement 1**: "It is reduced to sulfur dioxide on reaction with copper."
- When concentrated sulfuric acid (H₂SO₄) reacts with copper (Cu), it indeed gets reduced to sulfur dioxide (SO₂). The reaction can be represented as:
\[ \text{Cu} + 2 \text{H}_2\text{SO}_4 \rightarrow \text{CuSO}_4 + \text{SO}_2 + 2 \text{H}_2\text{O} \]
- This statement is **correct**.

2. **Statement 2**: "Concentrated sulfuric acid is a strong dehydrating agent."
- Concentrated sulfuric acid is known for its dehydrating properties. For example, when it reacts with sucrose (C₁₂H₂₂O₁₁), it removes water and carbon is produced:
\[ \text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{SO}_4 \rightarrow 12 \text{C} + 11 \text{H}_2\text{O} \]
- Similarly, it dehydrates alcohols. Therefore, this statement is also **correct**.

3. **Statement 3**: "It can be used to manufacture more volatile acids from their corresponding salts."
- Concentrated sulfuric acid can indeed be used to produce more volatile acids from their salts. For example, sodium chloride (NaCl) reacts with concentrated sulfuric acid to produce hydrochloric acid (HCl):
\[ \text{NaCl} + \text{H}_2\text{SO}_4 \rightarrow \text{HCl} + \text{NaHSO}_4 \]
- This statement is **correct**.

4. **Statement 4**: "The absorption of sulfur dioxide in sulfuric acid produces oleum."
- This statement is incorrect. Oleum (H₂S₂O₇) is produced when sulfur trioxide (SO₃) is dissolved in concentrated sulfuric acid, not sulfur dioxide (SO₂). The correct reaction is:
\[ \text{SO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{H}_2\text{S}_2\text{O}_7 \]
- Therefore, this statement is **not correct**.

Based on the analysis, the statement that is not correct is:

**Answer**: The absorption of sulfur dioxide in sulfuric acid produces oleum.