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 $Cr ( OH )_{3}$

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 $CrO \left( O _{2}\right)_{2}$ is formed. The chemical reaction is as follows

$Cr _{2} O _{7}^{2-}+2 H ^{+}+4 H _{2} O _{2} \rightarrow 2 CrO \left( O _{2}\right)_{2}+5 H _{2} O$