Four colourless salt solutions are placed in separation test tubes and a strip of copper is dipped in each. Which solution finally turns blue? (use data from electrochemical series

Options

A. `Pb(NO_(3)_(2)`
B. `AgNO_(3)`
C. `Zn(NO_(3)_(2)`
D. `Cd(NO_(3)_(2)`

Answer

To determine which colorless salt solution will turn blue when a strip of copper is dipped into it, we need to analyze the electrochemical properties of the metals involved, specifically their standard reduction potentials.

### Step-by-Step Solution:

1. **Identify the Electrochemical Series**:
We need to refer to the standard reduction potentials of the metals involved. The relevant metals here are Copper (Cu), Lead (Pb), Silver (Ag), Cadmium (Cd), and Zinc (Zn).

2. **Standard Reduction Potentials**:
- Copper (Cu²⁺ + 2e⁻ → Cu): +0.34 V
- Lead (Pb²⁺ + 2e⁻ → Pb): -0.13 V
- Silver (Ag⁺ + e⁻ → Ag): +0.80 V
- Cadmium (Cd²⁺ + 2e⁻ → Cd): -0.40 V
- Zinc (Zn²⁺ + 2e⁻ → Zn): -0.76 V

3. **Determine Oxidizing and Reducing Agents**:
In this scenario, copper will act as a reducing agent, and we need to find a solution that contains a metal ion that can oxidize copper. This means we are looking for a metal ion with a higher reduction potential than copper.

4. **Comparison of Reduction Potentials**:
- Silver (Ag) has a reduction potential of +0.80 V, which is higher than copper's +0.34 V.
- Lead, Cadmium, and Zinc all have negative potentials, meaning they cannot oxidize copper.

5. **Conclusion**:
Since Silver (Ag) can oxidize copper due to its higher reduction potential, when copper is dipped into a solution containing Ag⁺ ions, the copper will be oxidized to Cu²⁺, and the Ag⁺ ions will be reduced to Ag. The formation of Cu²⁺ ions in solution will give it a blue color.

Thus, the solution that will turn blue is the one containing silver ions (Ag⁺).

### Final Answer:
The solution that will turn blue is the one containing Silver (Ag⁺) ions.