What happens to pale blue ppt. obtained when ammonia solution is added to copper sulphate solution on addition of excess of alkali ?

Options

A. Ppt. is soluble
B. Ppt. is insoluble
C. No effect on ppt
D. Sparingly soluble

Explanation

To solve the question regarding the pale blue precipitate formed when ammonia solution is added to copper sulfate solution and what happens upon the addition of excess alkali, we can break down the process into clear steps.

### Step-by-Step Solution:

1. **Understanding the Initial Reaction**:
- When ammonia solution (NH₄OH) is added to copper sulfate solution (CuSO₄), a pale blue precipitate of copper hydroxide (Cu(OH)₂) is formed.
- The reaction can be represented as:
\[ \text{CuSO}_4 + 2\text{NH}_4\text{OH} \rightarrow \text{Cu(OH)}_2 \downarrow + \text{(NH}_4)_2\text{SO}_4 + \text{H}_2\text{O} \]
- Here, Cu(OH)₂ is the pale blue precipitate.

2. **Addition of Excess Alkali**:
- When excess alkali (ammonium hydroxide) is added to the solution containing the pale blue precipitate, a complex ion is formed.
- The copper hydroxide reacts with the excess ammonium hydroxide to form a soluble complex:
\[ \text{Cu(OH)}_2 + 4\text{NH}_4\text{OH} \rightarrow \text{[Cu(NH}_3\text{)}_4]^{2+} + 2\text{H}_2\text{O} \]
- This complex is known as tetraamminecopper(II) sulfate.

3. **Conclusion**:
- The pale blue precipitate (Cu(OH)₂) dissolves in the presence of excess alkali, forming a soluble complex ion. Therefore, the initial precipitate is no longer visible as it has dissolved.

### Final Answer:
The pale blue precipitate obtained from the reaction of ammonia with copper sulfate dissolves upon the addition of excess alkali, forming a soluble complex.