The equilibrium `Cr_(2)O_(7)^(2-)hArr 2CrO_(4)^(2-)`

Options

A. exist in acidic medium
B. exists in basic medium
C. Exists in neutral medium
D. It does not exist

Answer

To analyze the equilibrium reaction \( \text{Cr}_2\text{O}_7^{2-} \rightleftharpoons 2\text{CrO}_4^{2-} \), we need to consider the behavior of these species in different pH environments: acidic, basic, and neutral.

### Step-by-Step Solution:

1. **Identify the Species Involved**:
- The reaction involves dichromate ion \( \text{Cr}_2\text{O}_7^{2-} \) and chromate ion \( \text{CrO}_4^{2-} \).

2. **Consider the Medium**:
- The behavior of these ions changes depending on the pH of the solution (acidic, basic, or neutral).

3. **Acidic Medium**:
- In an acidic medium, the dichromate ion \( \text{Cr}_2\text{O}_7^{2-} \) is favored. The equilibrium shifts to the left, where chromate ions \( \text{CrO}_4^{2-} \) can react with hydrogen ions \( \text{H}^+ \) to form \( \text{Cr}_2\text{O}_7^{2-} \).
- Reaction: \( \text{CrO}_4^{2-} + 2\text{H}^+ \rightleftharpoons \text{Cr}_2\text{O}_7^{2-} + \text{H}_2\text{O} \)

4. **Basic Medium**:
- In a basic medium, the dichromate ion reacts with hydroxide ions \( \text{OH}^- \) to form chromate ions. The equilibrium shifts to the right, favoring the formation of \( \text{CrO}_4^{2-} \).
- Reaction: \( \text{Cr}_2\text{O}_7^{2-} + 2\text{OH}^- \rightleftharpoons 2\text{CrO}_4^{2-} + \text{H}_2\text{O} \)

5. **Neutral Medium**:
- In a neutral medium, there is a balance between the two ions, but neither ion is favored significantly. The equilibrium can be represented as:
- Reaction: \( \text{Cr}_2\text{O}_7^{2-} + \text{H}_2\text{O} \rightleftharpoons 2\text{CrO}_4^{2-} + \text{H}^+ \)

6. **Conclusion**:
- The equilibrium \( \text{Cr}_2\text{O}_7^{2-} \rightleftharpoons 2\text{CrO}_4^{2-} \) predominantly exists in a basic medium, where chromate ions are more stable compared to dichromate ions.

### Final Answer:
The equilibrium \( \text{Cr}_2\text{O}_7^{2-} \rightleftharpoons 2\text{CrO}_4^{2-} \) exists predominantly in a basic medium.

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