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
Show Hint
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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