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alcohol test by k2cr2o7 how colour chnage from orange to green

alcohol test by k2cr2o7 how colour chnage from orange to green


Grade:12th pass

1 Answers

Aarti Gupta
askIITians Faculty 300 Points
6 years ago
Alcohols react with oxidising agent like potassium dichromate,K2Cr2O7 in dil.H2SO4.However the differnt alcohols react differently during this reaction.
When alcohol treated with acidified K2Cr2O7,if reacton occurs, orange colour solution containing dichromate ions get reduced to green solution containing chromium ions.The electron half equation for this reaction can be given as-
Cr2O72- + 14H+ + 6e- ---------------> 2Cr3+ + 7H2O
Primary and secondary alcohols give this test but tertiary not.So colour of acidified potassium dichromate gets changes from orange to green.Primary alcohols oxidised to first aldehyde and then to acids.But secondary alcohols oxidised to ketone which further not oxidised.

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