Question

When hydrogen peroxide is treated with a cold acidified K2Cr2O7 solution containing ether, a blue colour is obtained. This is due to :

• A. Chromium sulphate.
• B. Potassium chromate.
• C. Perchromic acid.
• D. Chromium trioxide.

Answer 1

Answer: (C)

Perchromic acid.

Answer 2

A solution of K2Cr2O7 in H2SO4 is oxidised to blue cromic acid by H2O2 and dissolve in ether to give blue coloured solution.

K2Cr2O7 + H2SO4 $\longrightarrow$K2SO4 + H2Cr2O7

H2Cr2O7 + 4H2O2 $\longrightarrow$2CrO5 + 5H2O

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K2Cr2O7 + H2SO4 + 4H2O2$\longrightarrow$K2SO4 + 2CrO5

        Percromic acid (blue) + 5H2O