`CuSO_(4)+KCN(excess) to K_(3)[Cu(CN)_(4)]+(1)/(2)(CN)_(2)`

Options

A. For coloured ppt./Black ppt
B. For coloured solution.
C. for clear/colourless solution
D. For white ppt.

Answer

To solve the reaction \( \text{CuSO}_4 + \text{KCN (excess)} \rightarrow \text{K}_3[\text{Cu(CN)}_4] + \frac{1}{2} \text{CN}_2 \), we will analyze the products formed and determine their characteristics, particularly focusing on their color.

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
- The reactants are copper(II) sulfate (\( \text{CuSO}_4 \)) and potassium cyanide (\( \text{KCN} \)).
- The products are potassium tetracyanocuprate(II) (\( \text{K}_3[\text{Cu(CN)}_4] \)) and cyanogen (\( \frac{1}{2} \text{CN}_2 \)).

2. **Analyze the Product \( \frac{1}{2} \text{CN}_2 \)**:
- Cyanogen (\( \text{CN}_2 \)) is a colorless gas. Therefore, this product does not contribute any color to the solution.

3. **Examine the Complex Ion \( \text{K}_3[\text{Cu(CN)}_4] \)**:
- This complex contains copper as the central metal ion and cyanide ions as ligands.
- To determine the color of this complex, we need to analyze the oxidation state of copper in the complex.

4. **Determine the Oxidation State of Copper**:
- Let the oxidation state of copper be \( x \).
- The oxidation states of potassium (K) is +1 and cyanide (CN) is -1.
- The equation for charge balance is:
\[ 3(+1) + x + 4(-1) = 0 \]
Simplifying this gives:
\[ 3 + x - 4 = 0 \implies x = +1 \]
- Thus, copper is in the +1 oxidation state in the complex.

5. **Electronic Configuration of Copper in +1 State**:
- The electronic configuration of neutral copper (Cu) is \( [\text{Ar}] 3d^{10} 4s^1 \).
- In the +1 oxidation state, copper loses one electron from the 4s orbital, resulting in \( [\text{Ar}] 3d^{10} \).

6. **Determine the Electron Configuration**:
- In the \( 3d^{10} \) configuration, all d-electrons are paired.
- Since there are no unpaired electrons, there will be no d-d transitions.

7. **Conclusion on Color**:
- Because there are no unpaired electrons in the \( \text{K}_3[\text{Cu(CN)}_4] \) complex, it will not exhibit color due to the absence of d-d transitions.
- Therefore, both products (the complex and cyanogen) are colorless.

8. **Final Answer**:
- The correct option is **C**, which corresponds to a clear colorless solution.