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  4. Acidic dichromate ion reacts with hydrogen peroxide to give deep blue colour. This is due to the formation of

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Q. Acidic dichromate ion reacts with hydrogen peroxide to give deep blue colour. This is due to the formation of

ManipalManipal 2020

Solution:

When cold $H _{2} O _{2}$ is added in cold mixture of $K _{2} Cr _{2} O _{7}$ and conc. $H _{2} SO _{4}$ (i.e. $K _{2} Cr _{2} O _{7}$ in acidic medium), a deep blue solution of blue perchromate is obtained as,
$K _{2} Cr _{2} O _{7}+ H _{2} SO _{4} \rightarrow K _{2} SO _{4}+ H _{2} Cr _{2} O _{7}$
$H _{2} Cr _{2} O _{7}+4 H _{2} O _{2} \rightarrow \underset{\text{Blue per chromate}}{2 CrO _{5}+5 H _{2} O}$