Question

Assertion: Change in colour of acidic solution of potassium dichromate by breath is used to test drunk drivers.
Reason: Change in colour is due to the complexation of alcohol with potassium dichromate.
A.Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.
B.Both Assertion and Reason are correct but the Reason is not the correct explanation of the Assertion.
C.Assertion is correct but Reason is incorrect
D.Assertion is incorrect but the Reason is correct

Answer 1

The oxidation of alcohol with an acidic solution of potassium dichromate is the main reason for the change of colour. Potassium dichromate in the presence of dilute sulphuric acid acts as an oxidizing agent. Then, it gets converted into chromic sulphate whose colour is green.

Complete step by step answer:
The chemical formula of potassium dichromate is ${K_2}C{r_2}{O_7}$. Potassium dichromate is orange in colour. It is the inorganic chemical reagent which is mostly used as an oxidizing agent. It is the weak paramagnetic compound. It has all hexavalent chromium compounds, which can be harmful to health. It is a highly corrosive compound.
Potassium dichromate can oxidize iodide to iodine. It can also be used for dyeing, staining, tanning etc. When it is heated, it gives out toxic chromium fumes, so it can be used for medical purposes.
Now, according to the question, due to its property of oxidation, when the alcohol reacts with potassium dichromate, it forms acetic acid. When this reaction is going on, the dichromate ion which is reddish – orange converts to the green chromium ion. The degree of the color change is directly related to the level of alcohol in the exhaled air.
Hence, the assertion is correct but the reason given in the question is incorrect.

Hence, the correct option is (C).

Note: On the decomposition reaction of potassium dichromate it can form potassium chromate, chromic oxide and oxygen.
As potassium dichromate is a good oxidizing agent, it can be used in the labs and industry for various purposes.