Question

The equilibrium \( \text{Cr}_2\text{O}_7^{2-} \rightleftharpoons 2\text{CrO}_4^{2-} \):

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

Hint:

The chromate-dichromate equilibrium is a classic example of Le Chatelier’s Principle, where the reaction shifts based on pH.

Answer 1

The Correct Option is A

The pH level influences the equilibrium between dichromate (\( \text{Cr}_2\text{O}_7^{2-} \)) and chromate (\( \text{CrO}_4^{2-} \)) ions. Dichromate ions are prevalent in acidic conditions. Conversely, in basic conditions, the equilibrium favors chromate ions because hydroxide ions (\( OH^- \)) neutralize \( H^+ \) ions in the solution. This reaction is represented as: \[\text{Cr}_2\text{O}_7^{2-} + 2OH^- \rightleftharpoons 2\text{CrO}_4^{2-} + H_2O\] Consequently, chromate ions are the dominant species in a basic environment.