Question

In an acidified solution of $K_{2}Cr_{2}O_{7}$ $,H_{2}O_{2}$ is added. Then

• A. solution turns green due to formation of $Cr_{2}O_{3}$
• B. solution turns yellow due to formation of $K_{2}CrO_{4}$
• C. a blue coloured compound $CrO\left(O_{2}\right)_{2}$ is formed
• D. solution gives green precipitate of $Cr\left(\right.OH\left(\left.\right)_{3}$

Answer 1

Answer: (C)

Hydrogen peroxide acts as an oxidising as well as a reducing agent in both acidic and alkaline media.
When $H_{2}O_{2}$ is added to an acidified potassium dichromate solution, the blue coloured compound $CrO_{5}$ or $CrO\left(\right.O_{2}\left(\left.\right)_{2}$ is formed. The chemical reaction is as follows
$\left(Cr\right)_{2}O_{7}^{2 -}+2H^{+}+4H_{2}O_{2} \rightarrow 2CrO\left(O_{2}\right)_{2}$ $+$ $5H_{2}O$