Question

A colourless gas G is produced when egg-shells are treated with a solution S. The gas G turns lime water milky. S and G respectively are:

• A. \( \text{H}_2\text{SO}_4 \) and \( \text{SO}_2 \)
• B. \( \text{HCl} \) and \( \text{SO}_2 \)
• C. \( \text{NaCl} \) and \( \text{CO}_2 \)
• D. \( \text{HCl} \) and \( \text{CO}_2 \)

Answer 1

The Correct Option is D

Step 1: Eggshell and Solution Reaction:
Eggshells are primarily calcium carbonate (CaCO₃). This compound reacts with acidic solutions to produce a colorless gas. This gas, when bubbled through lime water, causes it to turn milky, signifying the presence of carbon dioxide (CO₂).

Step 2: Solution (S) Analysis:
The solution reacting with eggshells to yield a colorless gas must be acidic because acids react with calcium carbonate to release CO₂. Hydrochloric acid (HCl) is a common acid used in this reaction. The reaction between calcium carbonate and hydrochloric acid is:
\[\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2\]In this equation, the acid (HCl) reacts with calcium carbonate (CaCO₃) to produce carbon dioxide (CO₂), water (H₂O), and calcium chloride (CaCl₂).

Step 3: Gas (G) Analysis:
The gas produced is carbon dioxide (CO₂), which is colorless. It reacts with lime water (a calcium hydroxide, Ca(OH)₂, solution) to form calcium carbonate, resulting in a milky appearance:
\[\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}\]This reaction confirms the gas is CO₂.

Step 4: Conclusion:
The solution (S) is HCl (hydrochloric acid), and the colorless gas (G) is CO₂ (carbon dioxide). When CO₂ is passed through lime water, it becomes milky due to the formation of calcium carbonate.