Potassium ferrocyanide is used in the detection of

Options

A. `Fe^(2+)` ions
B. `Fe^(3+)` ions
C. `Cu^(2+)` ions
D. `Cd^(2+)` ions

Answer

**Step-by-Step Solution:**

1. **Understanding Potassium Ferrocyanide**: Potassium ferrocyanide is represented by the chemical formula K₄[Fe(CN)₆]. It is commonly used as a reagent in qualitative analysis to detect certain metal ions.

2. **Reactions with Metal Ions**:
- **Detection of Fe²⁺ Ions**: When potassium ferrocyanide reacts with ferrous ions (Fe²⁺), it forms a bluish-white precipitate of K₂[Fe₂(CN)₆]. This indicates the presence of Fe²⁺ ions.
- Reaction:
\[ \text{Fe}^{2+} + 2 \text{K}_4[\text{Fe(CN)}_6] \rightarrow K_2[\text{Fe}_2(\text{CN})_6] \text{ (bluish-white precipitate)} \]

- **Detection of Fe³⁺ Ions**: When potassium ferrocyanide reacts with ferric ions (Fe³⁺), it produces a blue precipitate known as Prussian blue, which is represented as Fe₃[Fe(CN)₆]. This indicates the presence of Fe³⁺ ions.
- Reaction:
\[ 3 \text{Fe}^{3+} + 2 \text{K}_4[\text{Fe(CN)}_6] \rightarrow \text{Fe}_3[\text{Fe(CN)}_6] \text{ (Prussian blue precipitate)} \]

- **Detection of Cu²⁺ Ions**: When copper(II) ions (Cu²⁺) react with potassium ferrocyanide, they form a chocolate brown precipitate of Cu₂[Fe(CN)₆]. This indicates the presence of Cu²⁺ ions.
- Reaction:
\[ 2 \text{Cu}^{2+} + 2 \text{K}_4[\text{Fe(CN)}_6] \rightarrow \text{Cu}_2[\text{Fe(CN)}_6] \text{ (chocolate brown precipitate)} \]

3. **Conclusion**: Based on the reactions above, potassium ferrocyanide can be used to detect the presence of Fe²⁺, Fe³⁺, and Cu²⁺ ions. However, it does not react with cadmium ions (Cd²⁺), thus cannot be used for their detection.

**Final Answer**: Potassium ferrocyanide is used in the detection of Fe²⁺, Fe³⁺, and Cu²⁺ ions.

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