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Question
Describe the oxidising action of potassium dichromate and write the ionic equation for its reaction with H2S.
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Solution
Potassium dichromate acts as a strong oxidising 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)
H2S is oxidised to sulphur.
\[\ce{Cr2O^2-_7 + 8H^+ + 3H2S -> 2Cr^3+ + 7H2O + 3S}\]
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