Question

Which one is correct for breath analysers used to test drivers suspected of drinking?
A. It works on the basis of redox reaction.
B. The drunken drivers breath is allowed to pass through acidified ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$ solution.
C. The colour change of ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$ solution is detected to test drunk level in breath.
D. Alcohol vapours coming out with breath are oxidized to acetic acid in breath analyser.

Answer 1

Hint: A breath analyser is a device used to estimate the presence of alcohol content in the blood.

Complete step by step answer: The breath analyser is made up of a chamber. The chamber contains potassium dichromate $\left( {{{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}} \right)$, sulfuric acid and silver nitrate.
When the drunken drivers breath is allowed to pass through acidified ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$ solution, the ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$ solution reacts with alcohol from the breath and loses an oxygen atom.
The process where an oxygen atom is lost is known as reduction. Thus, the reduction of ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$ occurs.
After reduction, the orange coloured solution of ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$ turns green in colour. The green colour is due to the presence of chromium sulfate.
Thus, the colour change of ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$ solution confirms the presence of alcohol in breath of drunken driver.
Also, the vapours of alcohol coming out with breath lose hydrogen atoms and get oxidized to acetic acid. Thus, an oxidation reaction of alcohol occurs.
Oxidation and reduction reactions occur simultaneously. Thus, when ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$ gets reduced, alcohol gets oxidized.
When oxidation and reduction reaction occurs simultaneously, the reaction is collectively known as redox reaction.
Thus, the breath analyser works on the basis of redox reaction.
Thus, all the statements for the breath analyser used to test drivers suspected of drinking are correct.
Thus, the correct options are option (A), (B), (C) and (D).

Note: The presence of alcohol in the breath is detected by the change in colour of the acidified ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}$ solution from orange to green. Another way to detect the presence of alcohol in breath is by measuring the electric current produced by the reaction.