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Q42 (CDS-II/2010) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Applied everyday chemistry Answer Verified

The law enforcement agencies use a chemical test to approximate a person’s blood alcohol level. The person under going the test blows into the mouthpiece of a bag containing sodium dichromate solution in acidic medium. A chemical reaction with ethanol changes the colour of the solution from

Result
Your answer: —  ·  Correct: A
Explanation

Law enforcement agencies use breathalyzers to estimate blood alcohol levels through a redox reaction. When a person blows into the device, ethanol in their breath reacts with an acidified sodium or potassium dichromate solution [t1][t2]. In this reaction, the ethanol is oxidized to ethanal or ethanoic acid, while the dichromate ions (Cr2O7^2-) are reduced to chromium(III) ions (Cr3+) [t1][t7]. The dichromate ion is characterized by a distinct orange color, whereas the resulting chromium(III) ions are green [t3][t5]. Consequently, the presence of alcohol is indicated by a visible color change from orange to green [t1][t10]. The intensity of this color change is proportional to the concentration of alcohol in the breath sample [t1]. This chemical principle allows for a quick, non-invasive approximation of intoxication levels based on the reduction of the transition metal complex [t7][t9].

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