Question

PCl$_3$ is stored in a well stoppered bottle since

• A. It decomposes in the presence of moisture
• B. It is decomposed by light
• C. It is highly volatile
• D. It reacts with air to form POCl$_3$
• E. (A) and (C)

Hint:

Compounds that "fume in air," like $PCl_3$ and $SiCl_4$, are actually reacting with atmospheric moisture to produce visible $HCl$ acid droplets.

Answer 1

The Correct Option is A

Concept: The storage of phosphorus trichloride is dictated by its high reactivity with atmospheric water vapor, leading to hydrolysis.

Step 1: {Identify the chemical reaction with moisture.}
$PCl_3$ reacts readily with water or moisture in the air to undergo hydrolysis, producing phosphorous acid and hydrogen chloride gas: $$PCl_3 + 3H_2O \rightarrow H_3PO_3 + 3HCl$$

Step 2: {Observe physical changes in air.}
When exposed to air, the $HCl$ gas produced reacts with moisture to form white fumes. This indicates the decomposition of the original sample.

Step 3: {Determine the storage requirement.}
To maintain the purity of the chemical and prevent the formation of acidic fumes, it must be kept in a tightly sealed container to exclude all moisture.