Science and Technology question from JKAS Prelims, 2022 by JKPSC
The device used by traffic police in breath tests for drunk driving works on the principle of:
Last updated Jun 24, 2026
Correct Answer:
Option A —
Potassium dichromate with sulphuric acid
The breathalyzer test used by traffic police is a classic example of an Oxidation-Reduction (Redox) reaction.The Principle: The device contains a solution of Potassium dichromate ($K_2Cr_2O_7$) dissolved in Sulphuric acid ($H_2SO_4$).The Reaction: When a driver blows into the device, any ethanol (alcohol) in their breath reacts with the orange potassium dichromate. The alcohol is oxidized to acetic acid, and the chromium is reduced from an oxidation state of $+6$ to $+3$.The Color Change: This chemical change causes a visible transition from Orange to Green. The intensity of the green color is proportional to the concentration of alcohol in the breath.
Conclusion:
The specific chemical reaction used to detect ethanol via a colorimetric change involves the acidified potassium dichromate solution.
Answer verified by Quintessence Classes faculty — Karan Nagar, Srinagar.
