Question

When $H_2O_2$ is added to an acidified $K_2Cr_2O_7$ solution

• A. A green colour solution is obtained
• B. A yellow solution is obtained
• C. A blue-violet solution is obtained
• D. A green precipitate is formed

Answer 1

Answer: (C)

A blue-violet solution is obtained

Answer 2

On adding $H _{2} O _{2}$ in acidic solution of $K _{2} Cr _{2} O _{7}$, $H _{2} O _{2}$ oxidisc it to $CrO _{5}$ (chromic penta oxidc/ chromic per oxide) and gives the blue-violet solution.

$K _{2} Cr _{2} O _{7}+ H _{2} SO _{4}+4 H _{2} O _{2} \longrightarrow K _{2} SO _{4}+2 CrO _{5}

+ 5 H _{2} O$

$CrO _{5}$ on decomposition gives oxygen

$4 CrO _{5}+6 H _{2} SO _{4} \longrightarrow Cr _{2}\left( SO _{4}\right)_{3}+6 H _{2} O +7 O _{2}$