The equilibrium: `2Cu^(1) Leftrightarrow Cu^0+ Cu^(u)` in aqueous medium at `25^@C` shifts towards the left in the presence of

Options

A. `NO_(3)^(-)`
B. `Cl^(-)`
C. `SCN^(-)`
D. `CN^(-)`

Answer

To solve the question regarding the equilibrium `2Cu^(1+) ⇌ Cu^0 + Cu^(2+)` in an aqueous medium at `25°C`, we need to analyze how the equilibrium shifts in response to the presence of certain ions.

### Step-by-Step Solution:

1. **Understanding the Equilibrium**:
The equilibrium involves copper ions in two oxidation states: Cu^(1+) and Cu^(2+). The reaction can be summarized as:
\[ 2Cu^{1+} \rightleftharpoons Cu^0 + Cu^{2+} \]
Here, Cu^0 is the elemental form of copper, Cu^(1+) is the +1 oxidation state, and Cu^(2+) is the +2 oxidation state.

2. **Identifying the Shift in Equilibrium**:
The question states that the equilibrium shifts towards the left. This means that the concentration of Cu^(1+) will increase while the concentration of Cu^(2+) will decrease.

3. **Role of Reducing Agents**:
For the equilibrium to shift to the left, Cu^(2+) must be reduced to Cu^(1+). A reducing agent is a substance that donates electrons to another substance, thus reducing it. In this case, the presence of certain ions can act as reducing agents.

4. **Analyzing the Ions**:
The ions mentioned in the video transcript are nitrate ion (NO3^-), chloride ion (Cl^-), thiocyanate ion (SCN^-), and cyanide ion (CN^-). We need to determine which of these can act as reducing agents:
- **Nitrate ion (NO3^-)**: This ion is in its highest oxidation state (+5) and cannot act as a reducing agent.
- **Chloride ion (Cl^-)**: This ion can be oxidized to Cl2, thus it can act as a reducing agent.
- **Thiocyanate ion (SCN^-)**: This ion can also be oxidized, hence it can act as a reducing agent.
- **Cyanide ion (CN^-)**: This ion can be oxidized as well, making it a reducing agent.

5. **Conclusion**:
The presence of chloride ion (Cl^-), thiocyanate ion (SCN^-), and cyanide ion (CN^-) will shift the equilibrium to the left by reducing Cu^(2+) to Cu^(1+). Therefore, the correct answer is that the equilibrium shifts towards the left in the presence of Cl^-, SCN^-, and CN^-.

### Final Answer:
The equilibrium `2Cu^(1+) ⇌ Cu^0 + Cu^(2+)` shifts towards the left in the presence of chloride ion (Cl^-), thiocyanate ion (SCN^-), and cyanide ion (CN^-).

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