NEET Chemistry Hydrogen Questions Solved

NEET - 2014

In acidic medium, H2O2 changes Cr2O72- to CrO5 which has two (-O-O-) bonds. Oxidation state of Cr in CrO5 is

(a) +5

(b) +3

(c) +6

(d) -10

(c) When H2O2 is added to an acidified solution of a dichromate Cr2O72-, a deep blue coloured complex, chromic powder, CrO5 [or CrO(O2)2] is formed.

Cr2O72- + 2H+ + 4H2O2          2CrO(O2)2 + 5H2O                                                   Chromic peroxide

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

                              X= +6

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