Question

In acidic medium, $H_2{O}_2$ changes $C{r}_2{O}_7^{2-}$ to $Cr{O}_5$ which has two (-O-O-) bonds.
Oxidation state of Cr in $Cr{O}_5$ is

• A. +5
• B. +3
• C. +6
• D. -10

Answer 1

Answer: (C)

When $H_2{O}_2$ is added to an acidified solution of a dichromate $C{r}_2{O}_7^{2-},$ a deep blue coloured complex, chromic peroxide $Cr{O}_5[orCrO(O_2{)}_2]$ is formed.
$C{r}_2{O}_7^{2-}+2H^{+}+4H_{2}O\to \underset{Chromicperoxide}{\underbrace{2CrO(O_2{)}_2}}$
$+5H_{2}O$
This deep blue coloured complex has the following structure
Oxidation state of Cr is +6 due to the presence of two peroxide linkages which can be calculated as
Cr peroxide normal $x+(-1)4+(-2)=0,x-6=0$ and $x=+6$