The aqueous solution of potash alum `[K_(2)SO_(4)*Al_(2)(SO_(4))_(3)*24H_(2)O]` is acidic due to

Options

A. hydrolysis of `K^+`
B. hydrolysis of `Al^(3+)`
C. hydrolysis of `SO_(4)^(2-)`
D. Presence of acid in its crystal as impurity.

Answer

To determine why the aqueous solution of potash alum \([K_{2}SO_{4} \cdot Al_{2}(SO_{4})_{3} \cdot 24H_{2}O]\) is acidic, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components of Potash Alum**:
Potash alum is a double sulfate of potassium and aluminum. Its formula can be broken down into its constituent parts:
- Potassium sulfate \((K_{2}SO_{4})\)
- Aluminum sulfate \((Al_{2}(SO_{4})_{3})\)
- Water of crystallization \((24H_{2}O)\)

2. **Understand the Nature of the Ions in Solution**:
When potash alum dissolves in water, it dissociates into its ions:
\[ K^{+}, \quad Al^{3+}, \quad SO_{4}^{2-} \]
Here, \(K^{+}\) is a cation from a strong base (potassium hydroxide), and \(SO_{4}^{2-}\) is the anion from a strong acid (sulfuric acid).

3. **Analyze the Hydrolysis of the Aluminum Ion**:
The aluminum ion \((Al^{3+})\) is a small, highly charged cation that can hydrolyze in water:
\[ Al^{3+} + 6H_{2}O \rightleftharpoons [Al(H_{2}O)_{6}]^{3+} \rightleftharpoons Al(OH)_{3} + 3H^{+} \]
This reaction produces \(H^{+}\) ions, which contribute to the acidity of the solution.

4. **Consider the Contribution of Sulfate Ion**:
The sulfate ion \((SO_{4}^{2-})\) does not hydrolyze significantly in water, as it is the conjugate base of a strong acid (sulfuric acid). Therefore, it does not contribute to the basicity of the solution.

5. **Conclusion**:
The presence of \(H^{+}\) ions from the hydrolysis of \(Al^{3+}\) ions makes the solution acidic. Thus, the aqueous solution of potash alum is acidic due to the hydrolysis of aluminum ions, which results in the release of \(H^{+}\) ions.

### Final Answer:
The aqueous solution of potash alum is acidic due to the hydrolysis of aluminum ions, which produces \(H^{+}\) ions.

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