The correct option is **C. calcium carbonate is formed which on reaction with further carbon dioxide forms soluble calcium hydrogen carbonate**. ### Detailed Explanation: 1. **Understanding the Reaction**: - When carbon dioxide (CO₂) is bubbled into limewater (which is a dilute solution of calcium hydroxide, Ca(OH)₂), a chemical reaction occurs. The carbon dioxide reacts with calcium hydroxide to form calcium carbonate (CaCO₃), which is a white precipitate. The reaction can be represented as: \[ \text{Ca(OH)}_2 (aq) + \text{CO}_2 (g) \rightarrow \text{CaCO}_3 (s) + \text{H}_2\text{O} (l) \] - Here, CaCO₃ is the white precipitate that forms in the limewater. 2. **Continued Bubbling of CO₂**: - If the bubbling of carbon dioxide continues, the initially formed calcium carbonate reacts with the excess carbon dioxide. This leads to the formation of soluble calcium hydrogen carbonate (Ca(HCO₃)₂). The reaction can be represented as: \[ \text{CaCO}_3 (s) + \text{CO}_2 (g) + \text{H}_2\text{O} (l) \rightarrow \text{Ca(HCO}_3)_2 (aq) \] - Calcium hydrogen carbonate is soluble in water, which is why the white precipitate disappears. 3. **Why Option C is Correct**: - Option C accurately describes the process: calcium carbonate is formed initially, and upon further reaction with carbon dioxide, it dissolves to form soluble calcium hydrogen carbonate. This explains both the formation and subsequent disappearance of the precipitate. ### Why Other Options are Incorrect: - **Option A: Calcium carbonate is formed which on reaction dissolves**: - This option is partially correct in stating that calcium carbonate is formed and that it dissolves. However, it does not specify that the dissolution is due to the reaction with further carbon dioxide to form calcium hydrogen carbonate. Therefore, it lacks the complete explanation of the process. - **Option B: Calcium hydrogen carbonate is precipitated and then dissolves**: - This option is incorrect because calcium hydrogen carbonate does not precipitate; it is formed in solution. The initial precipitate is calcium carbonate, not calcium hydrogen carbonate. Thus, this option misrepresents the sequence of events. - **Option D: Concentration of the solution has occurred with the deposition of calcium hydroxide**: - This option is misleading. While calcium hydroxide is present in limewater, the process described does not involve the concentration of the solution or the deposition of calcium hydroxide. Instead, the key reactions involve the formation and dissolution of calcium carbonate and calcium hydrogen carbonate. ### Summary of Key Points: - Bubbling CO₂ into limewater forms a white precipitate of calcium carbonate. - Continued CO₂ bubbling leads to the formation of soluble calcium hydrogen carbonate, causing the precipitate to disappear. - The correct answer is C, as it accurately describes the chemical processes involved. - Understanding the sequence of reactions is crucial for grasping the behavior of carbon dioxide in limewater. This thorough understanding will help you tackle similar questions in your chemistry exams effectively!