Lime reacts exothermally with water to give ‘A’ which has low solubility in water. Aqueous solution of ‘A’ is often used for the test of CO2 , a test in which insoluble B is formed. If B is further reacted with CO2 then soluble compound is formed ‘A’ is
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Understanding the reactions of lime with water and carbon dioxide is important for many chemistry concepts. The solubility characteristics of the products are key to interpreting the given scenario.
- Quick lime
- Lime water
- Slaked lime
- White lime
The Correct Option is C
Solution and Explanation
Step 1: Reaction of CaO with Water (Forming 'A')
The reaction of calcium oxide (CaO) with water forms calcium hydroxide ('A'):
\[ \text{CaO}(s) + \text{H}_2\text{O}(l) \rightarrow \text{Ca(OH)}_2(aq) \]
The product, calcium hydroxide, is known as slaked lime, and its aqueous solution is called lime water.
Step 2: Reaction of 'A' with CO2 (Forming 'B')
The reaction of calcium hydroxide with carbon dioxide forms calcium carbonate ('B'):
\[ \text{Ca(OH)}_2(aq) + \text{CO}_2(g) \rightarrow \text{CaCO}_3(s) + \text{H}_2\text{O}(l) \]
The product, calcium carbonate, is insoluble in water.
Step 3: Reaction of 'B' with More CO2
When calcium carbonate reacts with more water and carbon dioxide, it forms calcium hydrogencarbonate, which is soluble in water:
\[ \text{CaCO}_3(s) + \text{H}_2\text{O}(l) + \text{CO}_2(g) \rightarrow \text{Ca(HCO}_3\text{)}_2(aq) \]
Final Answer:
The substance 'A' is calcium hydroxide (slaked lime).
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