Question

Chloroform is kept in dark bottles because of which of the following reasons?
A. It reacts with clear glass
B. It undergoes chlorination in transparent glass bottles
C. It is oxidized to a poisonous gas phosgene in sunlight
D. It starts burning when exposed to sunlight

Answer 1

Hint: Alkyl halides in presence of sunlight or ultraviolet light undergo substitution reaction specially known as photochemical reaction. The reaction involved:
Methane + Sunlight = Chloromethane + Hydrogen chloride
$C{H}_4+hv\to C{H}_{3}Cl+HCl$

Complete step by step answer:
Step 1:
Chloroform having formula $CHC{l}_3$ (trichloromethane) since, it is an alkyl halide and halogen generally has low bond dissociation enthalpy which means that halogen group in Chloroform can decompose to from free ions even at normal room temperature or when exposed to sunlight (using the ultraviolet radiation). Chloroform in the presence of sunlight reacts with air $\left(O_2\right)$ and undergoes oxidation reaction to form a compound, chemically named carbonyl chloride, commonly known as phosgene. The reaction involved is:
Chloroform + oxygen in air + sunlight = Phosgene + Hydrogen chloride
$2CHC{l}_3+O_2+hv\to 2COC{l}_2+HCl$
Step 2:
$COC{l}_2$ is Phosgene. Its IUPAC name is Carbonyl dichloride. Phosgene formed is a toxic gas, which is lethal and leads to death upon consumption. So, to prevent the formation of Phosgene gas, chloroform is kept in dark bottles.
So, the correct answer is “Option C”.

Note: $0\cdot 2-1\mathrm{\%}$ Ethanol is added in the bottles containing chloroform to prevent the effects of the poisonous gas phosgene. Ethanol reacts with phosgene to form a non-toxic compound as a precipitation product which is chemically called dimethyl carbonate. Moreover, the bottle should be tightly closed also to prevent air from getting inside the bottle.