Question

A “breath test” used by traffic police to check drunken driving uses ____?

Answer 1

Hint: Potassium dichromate acts as an oxidizing agent in presence of an acid. Oxidizing agent carries out oxidation of other compounds in a redox reaction while itself being reduced. Oxidation and reduction reaction occur simultaneously.

Complete Step by step answer: Potassium dichromate ${K_2}C{r_2}{O_7}$, is a common inorganic chemical reagent, and it is commonly used as an oxidizing agent in various reaction or processes. It is crystalline ionic solid with a very bright, red –orange color.
Potassium dichromate is an oxidizing agent in organic chemistry. It is milder than potassium permanganate. And in the laboratory it is used to oxidize alcohol. It converts primary alcohol to aldehydes and under some conditions alcohols can be oxidized to carboxylic acid. Secondary alcohols are converted into ketones. And tertiary alcohol cannot be oxidized.
Potassium dichromate has red- orange color. In the presence of an acid it acts as an oxidizing agent and converts ethanol to ethanoic acid.
The concentration of ethanol in a sample can be determined with the help of acidified potassium dichromate ${K_2}C{r_2}{O_7}$ solution. All the ethanol gets converted to acetic acid / ethanoic acid . the chemical reaction for this conversion is-
$3C{H_3}C{H_2}OH + 2{K_2}C{r_2}{O_7} + 8{H_2}S{O_4} \to 3C{H_3}COOH + 2C{r_2}{(SO4)_3} + 2{K_2}S{O_4} + 11{H_2}O$
Here the potassium dichromate is getting converted to chromium(III)sulphate .
The major application of this reaction is breath analyzer by traffic police in case of drunken driving. When a person who has consumed alcohol breathes into the analyzer, the potassium dichromate and sulphuric acid present in it makes contact with alcohol vapor. The redox reaction takes place, alcohol gets oxidized to acetic acid and the color of chromium changes from orange to green, as $Cr(III)$ appears as green color. The degree of color change is directly related to alcohol consumed.

Hence the answer is potassium dichromate – sulphuric acid solution

Note: Potassium dichromate paper can also be used to test for the presence of sulphur dioxide., as it turns from orange to green. Here also potassium dichromate acts as an oxidizing agent and gets converted to $Cr(III)$ which is of green color.