Oxidation of chloroform by air in the presence of sunlight produces a poisonous gas known as :
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Remember: Phosgene = Carbonyl Chloride = \( COCl_{2} \).
- Mustard gas
- Tear gas
- Chlorine gas
- Phosgene gas
The Correct Option is D
Solution and Explanation
• Chloroform (\( CHCl_{3} \)) is a volatile liquid that is highly sensitive to atmospheric oxygen and light exposure.
• When exposed to sunlight, it undergoes a slow chemical reaction known as atmospheric oxidation or photo-oxidation.
• The reaction leads to the formation of a carbonyl halide, which is an extremely toxic substance.
• This toxicity makes the storage of chloroform a critical safety concern in laboratories and industrial settings.
Step 1: Analyze the atmospheric oxidation process
In the presence of light (ultraviolet radiation), chloroform reacts with oxygen (\( O_{2} \)) from the air.
This reaction is facilitated by a free radical mechanism.
The presence of sunlight acts as a catalyst to initiate the cleavage of chemical bonds in chloroform.
Step 2: Determine the balanced chemical equation
The oxidation of chloroform follows the equation shown below:
\[ 2CHCl_{3} + O_{2} \xrightarrow{\text{light}} 2COCl_{2} + 2HCl \]
In this reaction:
\( CHCl_{3} \) represents Chloroform.
\( COCl_{2} \) represents Carbonyl chloride (the poisonous gas).
\( HCl \) represents Hydrogen chloride gas.
Step 3: Identify the common name of the product
The chemical compound \( COCl_{2} \) is systematically named as carbonyl chloride.
However, it is more famously known by its common name, Phosgene.
Phosgene is a colorless gas that was notoriously used as a chemical weapon during World War I due to its high toxicity.
Step 4: Explain prevention and stabilization methods
To prevent the formation of phosgene, chloroform is stored in dark, amber-colored bottles.
The bottles are filled completely to the brim to ensure no air (oxygen) is trapped inside.
Additionally, a small amount (\( 1\% \)) of ethyl alcohol (\( C_{2}H_{5}OH \)) is often added.
Ethanol reacts with any phosgene formed to create non-toxic diethyl carbonate:
\[ COCl_{2} + 2C_{2}H_{5}OH \rightarrow (C_{2}H_{5})_{2}CO_{3} + 2HCl \]
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