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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.
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Reason : Change in colour is due to the complexation of alcohol with potassium dichromate.
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Verified Answer
The correct answer is:
If assertion is true, but reason is false
Change in colour is due to the oxidation of alcohol with potassium dichromate. Oxidation of alcohols with $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ in dilute $\mathrm{H}_2 \mathrm{SO}_4$ (orange solution):
$\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ in presence of dilute $\mathrm{H}_2 \mathrm{SO}_4$ acts as an oxidising agent. It is converted into chromic sulphate which is green in colour.
$$
\begin{gathered}
\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7+4 \mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{K}_2 \mathrm{SO}_4+\mathrm{Cr}_2\left(\mathrm{SO}_4\right)_3+4 \mathrm{H}_2 \mathrm{O}+\frac{3}{2} \mathrm{O}_2 \\
\text { (orange) }
\end{gathered}
$$
(green)
$\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ in presence of dilute $\mathrm{H}_2 \mathrm{SO}_4$ acts as an oxidising agent. It is converted into chromic sulphate which is green in colour.
$$
\begin{gathered}
\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7+4 \mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{K}_2 \mathrm{SO}_4+\mathrm{Cr}_2\left(\mathrm{SO}_4\right)_3+4 \mathrm{H}_2 \mathrm{O}+\frac{3}{2} \mathrm{O}_2 \\
\text { (orange) }
\end{gathered}
$$
(green)
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