Question

Assertion: A small amount of alcohol is added to chloroform bottles.
Reason: Alcohol acts as an inhibitor for oxidation of chloroform. Also it reacts with $COC{l_2}$ to give harmless diethyl carbonate.
(A) Both assertion and reason are correct and reason is the correct explanation for assertion.
(B) Both assertion and reason are correct but reason is not the correct explanation for assertion.
(C) Assertion is correct but reason is incorrect.
(D) Both assertion and reason are incorrect.

Answer 1

Hint: Chloroform on exposure to sunlight and air gets oxidised to a highly toxic compound called phosgene. To prevent this it is stored in some special conditions.

Complete step by step answer:
-First of all let us see what chloroform is.
Chloroform has a molecular formula of $CHC{l_3}$ and hence is also known as trichloromethane. It is a colourless and dense liquid with strong smell and has applications as an anaesthetic, euphoriant, sedative, etc. It is also used as a precursor for different refrigerants.
-When a mixture of chlorine and methane ($C{H_4}$) or chloromethane ($C{H_3}Cl$). These precursors are converted to chlorinated compounds further by free radical halogenations.
                                   $C{H_4} + C{l_2} \to C{H_3}Cl + HCl$
                                   $C{H_3}Cl + C{l_2} \to C{H_2}C{l_2} + HCl$
                                   $C{H_2}C{l_2} + C{l_2} \to CHC{l_3} + HCl$

-Chloroform when exposed to sunlight and air, undergoes oxidation and releases a toxic gas known as phosgene ($COC{l_2}$) and hydrochloric acid (HCl).
                                        $CHC{l_3} + {O_2}\xrightarrow{{light}}COC{l_2} + HCl$

So, to prevent this chloroform is stored in dark, amber coloured bottles which are well stoppered and also small amounts of alcohol are added to these bottles.
The role of alcohol here is to act as a inhibitor for the oxidation of chloroform which means it doesn’t let the chloroform get oxidised into phosgene. Also if some phosgene is already present then it will react with it and form harmless diethyl carbonate.
                                     $COC{l_2} + 2{C_2}{H_5}OH \to {({C_2}{H_5}O)_2}CO + 2HCl$

Since we now know that both the assertion and reason are correct and also that reason is the correct explanation of the given assertion, the correct option will be:
Both assertion and reason are correct and reason is the correct explanation for assertion.
So, the correct answer is “Option A”.

Note: Phosgene is highly toxic and can be fatal at even small exposures of 50 ppm. It is also extremely harmful at exposure for less than 1 minute at 500 ppm level. Any human who has been exposed to phosgene might not feel any adverse effects immediately or instantaneously, but may lead to pulmonary edema in a few hours which may possibly lead to death within 24 hours.