Question

In an acidic medium, ${\mathrm{H}}_2{\mathrm{O}}_2$ changes ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ to ${\mathrm{CrO}}_5$. What is the oxidation state of $\mathrm{Cr}$ in ${\mathrm{CrO}}_5$?

• A. 2
• B. 3
• C. 5
• D. 6

Answer 1

The correct option is D

6

The Explanation for the correct answer

Option (D): $6$

• The balanced chemical equation will be: $\underset{\mathrm{Potassium}\mathrm{permanganate}}{{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7}+\underset{\mathrm{Sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4}+\underset{\mathrm{Hydrogen}\mathrm{peroxide}}{4{\mathrm{H}}_2{\mathrm{O}}_2}\to \underset{\mathrm{Chromium}\mathrm{peroxide}}{2{\mathrm{CrO}}_5}+\underset{\mathrm{Potassium}\mathrm{sulphate}}{{\mathrm{K}}_2{\mathrm{SO}}_4}+\underset{\mathrm{Water}}{5{\mathrm{H}}_2\mathrm{O}}$
• The structure of ${\mathrm{CrO}}_5$ has a double bond between $\mathrm{Cr}$ and $\mathrm{O}$ so Oxygen will have $-2$oxidation state here.
• Rest 4 Oxygens are of peroxide so Oxygen will have $-1$ oxidation state.

Let the oxidation state of $\mathrm{Cr}$ in ${\mathrm{CrO}}_5$ be $\mathrm{X}$.

$\Rightarrow \mathrm{X}+(-2)+4\times (-1)=0$

$\Rightarrow \mathrm{X}+(-2)+(-4)=0$

$\Rightarrow \mathrm{X}+(-6)=0$

$\Rightarrow \mathrm{X}=6$

The oxidation state of $\mathrm{Cr}$ in ${\mathrm{CrO}}_5$ is +6.

Hence, Option D is correct.