question_answer

In acidic \[{{H}_{2}}{{O}_{2}}\] reacts with dichromate to give coloured complex of \[Cr\]. Oxidation state of \[Cr\] in this complex is

A) \[+5\]

B) \[+3\]

C) \[+6\]

D) \[-10\]

Correct Answer: C

Solution :

When \[{{H}_{2}}{{O}_{2}}\] in added to an acidified solution of a dichromate, \[C{{r}_{2}}O_{7}^{2-}\], a deep blue coloured complex, chromic peroxide, \[Ca{{O}_{3}}\left[ or\,CrO{{\left( {{O}_{2}} \right)}_{2}} \right]\] is formed.

\[C{{r}_{2}}O_{7}^{2-}+2{{H}^{+}}+4{{H}_{2}}{{O}_{2}}\xrightarrow{{}}\] \[\underset{Chromic\,\,peroxide}{\mathop{2CrO{{\left( {{O}_{2}} \right)}_{2}}}}\,+5{{H}_{2}}O\]

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 In \[CrO{{\left( {{O}_{2}} \right)}_{2}}\], let the oxidation state of \[Cr\]be x.

\[x+(-1)4+(-2)=0\]

\[x-6=0\]

\[x=+6\]