Understanding Chloroform's Reaction with Oxygen and Light

Chloroform, also known as trichloromethane ($\text{CHCl}_3$), is a halogenated organic compound. It is a colorless, dense liquid with a characteristic ether-like odor. When chloroform is exposed to air (which contains oxygen) and light, it undergoes a chemical reaction. This reaction is an oxidation process.

The presence of light acts as a catalyst, initiating the reaction between chloroform and oxygen. The product formed is a highly toxic gas called phosgene.

Chemical Reaction of Chloroform Oxidation

The reaction between chloroform and oxygen in the presence of light can be represented by the following balanced chemical equation:

\begin{equation*} 2\text{CHCl}_3\text{(l)} + \text{O}_2\text{(g)} \xrightarrow{\text{Light}} 2\text{COCl}_2\text{(g)} + 2\text{HCl}\text{(g)} \end{equation*}

In this reaction:

• $\text{CHCl}_3$ is Chloroform
• $\text{O}_2$ is Oxygen
• $\text{COCl}_2$ is Phosgene (Carbonyl chloride)
• $\text{HCl}$ is Hydrogen chloride

Phosgene ($\text{COCl}_2$) is the primary and most significant product of this reaction, especially from the perspective of safe handling and storage of chloroform, as phosgene is extremely poisonous.

Analyzing the Options

Let's look at the provided options in the context of this reaction:

1. Chlorine gas ($\text{Cl}_2$): While chlorine is present in chloroform, chlorine gas is not the main product formed during its oxidation by oxygen in light. Hydrogen chloride ($\text{HCl}$) is produced as a byproduct, which involves chlorine.
2. Phosphine gas ($\text{PH}_3$): Phosphine is a compound of phosphorus and hydrogen. It has no relation to the oxidation product of chloroform, which contains carbon, oxygen, and chlorine.
3. Phosgene gas ($\text{COCl}_2$): As shown by the chemical equation, phosgene is the main toxic product formed when chloroform reacts with oxygen in the presence of light.
4. Hydrogen gas ($\text{H}_2$): Hydrogen gas is not produced in this oxidation reaction. Hydrogen from the chloroform molecule ends up in hydrogen chloride ($\text{HCl}$).

Based on the chemical transformation that occurs, phosgene gas is the product obtained.

Why This Reaction is Important

This reaction is important because it highlights a safety hazard associated with chloroform. Due to the formation of toxic phosgene, chloroform is typically stored in dark, airtight bottles, often with a small amount of ethanol added as a stabilizer. Ethanol reacts with any phosgene that might form, converting it into less toxic diethyl carbonate.

Revision Table: Chloroform Oxidation Product

Additional Information: Phosgene and Chloroform Storage

Phosgene ($\text{COCl}_2$):

• Phosgene is also known as carbonyl chloride.
• It is a colorless gas at room temperature, but can be stored as a liquid under pressure.
• It has a smell like newly mown hay or cut grass, though the odor may not be detectable at low, but still dangerous, concentrations.
• Phosgene is highly toxic and was used as a chemical weapon during World War I. Exposure can cause severe lung damage, often with delayed symptoms.

Chloroform Storage:

• To prevent the formation of phosgene, chloroform should be stored away from light and air.
• It is commonly kept in dark, amber-colored bottles with tight-fitting lids.
• Adding about 0.5% to 1% ethanol to chloroform acts as a stabilizer. Ethanol reacts with phosgene ($\text{COCl}_2$) to form diethyl carbonate ($\text{(C}_2\text{H}_5\text{O)}_2\text{CO}$) and hydrochloric acid ($\text{HCl}$), which are less harmful than phosgene itself:

\begin{equation*} \text{COCl}_2 + 2\text{C}_2\text{H}_5\text{OH} \rightarrow \text{(C}_2\text{H}_5\text{O)}_2\text{CO} + 2\text{HCl} \end{equation*}

This safety measure is crucial when working with or storing chloroform in a laboratory or industrial setting.