Why H2O2 reacts with K2Cr2O7 to give blue colour ?........

Why H2O2 reacts with K2Cr2O7 to give blue colour ?........


2 Answers

25758 Points
3 years ago
A blue colour is obtained when hydrogen peroxide is added to dichromate or any other Cr(VI) compound. The deep blue colour is due to formation of CrO(O2)2. The blue colour fades away and compound decomposes readily into Cr3+ and O2(g) in aqueous solution. However the peroxo compound can be extracted intoi oxygenated organic solvent e.g, diethyl ether, ethylacetate or 1-pentanol etc. where it remains stable. It is more stable below 273 K. On addition of pyridine to ethereal solution, it forms complex Py.Cro5.
231 Points
3 years ago
Let’s check out the reaction of hydrogen peroxide with acidified Potassium dichromate:
K2Cr2O7 + H2SO4 + 4H2O2 ------> K2SO4 + 2CrO5 + 5H2O
The formation of Chromium Pentaoxide leads to the formation of blue colour from orange (as potassium dichromate is orange in colour). Chromium Pentaoxide is blue in colour, so we get a blue colour after the reaction.
In the reaction, Hydrogen peroxide acts as an oxidizing agent, because it itself gets reduced, and its oxidation number changes to -2 from -1.

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