Acidified potassium dichromate () exhibits potent, targeted oxidising properties. During a direct re — d and f Block Elements Chemistry Question

💡 Solution & Explanation

Potassium dichromate is a strong oxidising agent in acidic media. When it reacts with $H_2S$, it oxidizes the sulfide ion ($S^{2-}$, oxidation state $-2$) directly to solid, elemental sulphur ($S$, oxidation state $0$), which precipitates out, making the solution turbid. The dichromate itself is reduced to the green $Cr^{3+}$ ion. The half reaction is: $H_2S \rightarrow S + 2H^+ + 2e^-$.