Class 12 NEET Chemistry D And F Block Elements Questions

Concept: Potassium dichromate acts as a strong oxidizing agent in an acidic medium and gets reduced to green-colored $\mathrm{Cr}^{3+}$ ions.Explanation:When sodium sulfite ($\mathrm{Na}_2\mathrm{SO}_3$) is added to an acidified solution of potassium dichromate ($\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7$), the dichromate ion oxidizes the sulfite ion to sulfate ($\mathrm{SO}_4^{2-}$). In this process, the dichromate ion ($\mathrm{Cr}^{6+}$) is reduced to the chromium(III) ion ($\mathrm{Cr}^{3+}$).The chemical reaction is:$$\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7 + 3\mathrm{Na}_2\mathrm{SO}_3 + 4\mathrm{H}_2\mathrm{SO}_4 \rightarrow \mathrm{Cr}_2(\mathrm{SO}_4)_3 + 3\mathrm{Na}_2\mathrm{SO}_4 + \mathrm{K}_2\mathrm{SO}_4 + 4\mathrm{H}_2\mathrm{O}$$The formation of chromium(III) sulfate, $\mathrm{Cr}_2(\mathrm{SO}_4)_3$, is responsible for the solution turning green.Answer: Option A