Q29 / 180 · COMEDK 2022 · Chemistry
The colour of $\mathrm{CrO}_4^{2-}$ changes to $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ is
- Correct answerAyellow to orange
- Borange to yellow
- Cyellow to blue
- Dorange to blue
Solution
The chromate ion $\mathrm{CrO}_4^{2-}$ is yellow in aqueous solution. In an acidic medium, the chromate ion undergoes dimerization to form the dichromate ion $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$, which is orange in color.
The equilibrium reaction is given by: $2\mathrm{CrO}_4^{2-} + 2\mathrm{H}^{+} \rightleftharpoons \mathrm{Cr}_2 \mathrm{O}_7^{2-} + \mathrm{H}_2 \mathrm{O}$.
Thus, the color change observed is from yellow to orange.
Answer: yellow to orange
The equilibrium reaction is given by: $2\mathrm{CrO}_4^{2-} + 2\mathrm{H}^{+} \rightleftharpoons \mathrm{Cr}_2 \mathrm{O}_7^{2-} + \mathrm{H}_2 \mathrm{O}$.
Thus, the color change observed is from yellow to orange.
Answer: yellow to orange
Hence, the correct answer is option: 'A'.