In the laboratory preparation of Chlorine, the gas is passed through a wash bottle of water to

Analysis of the Question

The question asks for the specific purpose of passing chlorine gas through a wash bottle containing water during its laboratory preparation.

Concept Explanation

In the laboratory, chlorine gas ($Cl_2$) is typically prepared by the reaction of concentrated hydrochloric acid ($HCl$) with an oxidizing agent like manganese(IV) oxide ($MnO_2$). The chemical equation is: $MnO_2(s) + 4HCl(aq) \rightarrow MnCl_2(aq) + 2H_2O(l) + Cl_2(g)$

Because concentrated $HCl$ is volatile, the chlorine gas produced is often contaminated with hydrogen chloride ($HCl$) gas fumes. To obtain pure chlorine gas, these impurities must be removed before the gas is collected.

Step-by-Step Solution

1. Identify the impurity: The gas produced is a mixture of $Cl_2$ and $HCl$ vapor.
2. Analyze the solubility: Hydrogen chloride ($HCl$) is extremely soluble in water. Chlorine gas ($Cl_2$), however, is only sparingly soluble in water.
3. The process: When the mixture is bubbled through water, the $HCl$ gas dissolves readily into the water, effectively "washing" the gas stream.
4. The result: The $Cl_2$ gas passes through the water relatively unaffected, while the $HCl$ is trapped in the wash bottle. (Note: A second wash bottle containing concentrated sulfuric acid is usually used afterward to dry the gas).

Conclusion

Passing the gas through water is a purification step specifically designed to remove the acidic $HCl$ impurity.

• Option A: Incorrect. Dilution does not purify the gas.
• Option B: Correct. Water effectively absorbs the highly soluble $HCl$ gas.
• Option C: Incorrect. While $HCl$ is an acid, the primary goal is purification by absorption, not neutralization.
• Option D: Incorrect. If the water absorbed the $Cl_2$ gas, you would not be able to collect the product.

Exam Tip

Always remember the "purification train" for chlorine gas:

1. Water: To remove $HCl$ gas.
2. Conc. $H_2SO_4$: To remove moisture (dry the gas).
3. Downward delivery: Because chlorine is denser than air.