Which of the following is formed when excess of KCN is added to an aqueous solution of copper sulphate?

Options

A. `Cu(CN)_(2)`
B. `K_(2)[Cu(CN)_(4)]`
C. `K[Cu(CN)_(2)]`
D. `K_(3)[Cu(CN)_(4)]`

Explanation

To determine which compound is formed when excess KCN is added to an aqueous solution of copper sulfate (CuSO4), we can follow these steps:

### Step 1: Identify the reactants
The reactants in this reaction are copper sulfate (CuSO4) and potassium cyanide (KCN).

### Step 2: Write the initial reaction
When KCN is added to CuSO4, the first reaction that occurs is the formation of a complex. The reaction can be represented as:
\[ \text{CuSO}_4 + 4 \text{KCN} \rightarrow \text{Cu(CN)}_2 + \text{K}_2\text{SO}_4 \]

### Step 3: Formation of the complex
In this step, the copper(II) ions from copper sulfate react with cyanide ions to form the complex copper(I) cyanide, which can be represented as:
\[ \text{Cu(CN)}_2 \]

### Step 4: Further reaction with excess KCN
Since KCN is in excess, the copper(I) cyanide can further react with more KCN to form a more stable complex:
\[ \text{Cu(CN)}_2 + 2 \text{KCN} \rightarrow \text{K}_3\text{Cu(CN)}_4 \]

### Step 5: Final product
The final product formed from the reaction of excess KCN with copper sulfate is:
\[ \text{K}_3\text{Cu(CN)}_4 \]

### Conclusion
Thus, the correct answer to the question is option D: \( K_3Cu(CN)_4 \).

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