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Question
Describe the oxidising action of potassium dichromate and write the ionic equation for its reaction with iodide.
Solution
Potassium dichromate acts as a strong oxidizing agent. It is used as a primary standard in volumetric analysis. The oxidation action of dichromate ion in an acidic medium can be represented as follows –
\[\ce{Cr2O^{2-}_7 + 14H^+ + 6e^- -> 2Cr^{3+} + 7H2O}\] (E– = 1.33 V)
The iodide ion (I−) is oxidised to I2 by the acidified solution of K2Cr2O7.
Reaction:
\[\ce{Cr2O^{2-}_7 + 14H^+ + 6I^- -> 2Cr^{3+} + 7H2O + 3I2 ^}\]
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