When `KHSO_(4)` is added into a concentrated solution of `H_(2)SO_(4)` the acidity of the solution.

Options

A. Increases
B. decreases
C. remains constant
D. can't be predicted

Answer

To solve the question regarding the effect of adding potassium hydrogen sulfate (KHSO₄) to a concentrated solution of sulfuric acid (H₂SO₄), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components**:
- When KHSO₄ is added to H₂SO₄, it dissociates into potassium ions (K⁺) and hydrogen sulfate ions (HSO₄⁻).
- The dissociation of KHSO₄ can be represented as:
\[ KHSO₄ \rightarrow K^+ + HSO₄^- \]

2. **Understand the Behavior of H₂SO₄**:
- H₂SO₄ is a strong acid and dissociates completely in two steps:
\[ H₂SO₄ \rightarrow H^+ + HSO₄^- \]
\[ HSO₄^- \rightarrow H^+ + SO₄^{2-} \]

3. **Common Ion Effect**:
- When KHSO₄ is added to the solution, the concentration of HSO₄⁻ ions increases due to the dissociation of KHSO₄.
- This increase in HSO₄⁻ concentration leads to a common ion effect, which shifts the equilibrium of the dissociation of H₂SO₄ backward according to Le Chatelier's principle.

4. **Effect on H⁺ Concentration**:
- The backward shift of the equilibrium results in a decrease in the concentration of H⁺ ions in the solution.
- Since the acidity of a solution is directly related to the concentration of H⁺ ions, a decrease in H⁺ concentration means a decrease in acidity.

5. **Conclusion**:
- Therefore, when KHSO₄ is added to a concentrated solution of H₂SO₄, the acidity of the solution decreases.

### Final Answer:
The acidity of the solution **decreases** when KHSO₄ is added to a concentrated solution of H₂SO₄. Thus, the correct option is **Option 2**.

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