The blue colour produced on adding `H_2O_2` to acidified `K_2Cr_2O_7` is due to the formation of

Options

A. `Cr_(2)O_(3)`
B. `CrO_(3)`
C. `CrO_(5)`
D. `CrO_(4)^(2-)`

Answer

C

Explanation

When hydrogen peroxide is added to an acidified solution of a dichromate (or any other Cr(+VI) species), a complicated reaction occurs. The products depend on the pH and the concentration of Cr
`Cr_(2)O_(7)^(2-)-+ 2H^(+) + 4H_(2)O_(2) to 2CrO(O_(2))_(2) + 5H_(2)O`
A deep blue-violet coloured peroxo compound `CrO(O_(2))_(2)` is formed. This decomposes rapidly in aqueous solution into `Cr^(3+)` and dioxygen. This peroxo compound can be extracted into ether, where it reacts with pyridine, forming the adduct py.`CrO(O_(2))_(2)`