Which of the following statements with regard to the reaction given below are correct? CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat
- 1. Quicklime is used for white-washing of walls.
- 2. The solution of slaked lime is used for whitewashing of walls.
- 3. CaO reacts slowly with CO₂ in air to form a thin layer of CaCO₃ on walls.
- 4. Calcium hydroxide called ‘slaked lime’ is an inorganic compound.
Select the correct answer using the code given below.
1 and 4 only
2 and 4
2 and 3
1, 3 and 4
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC CDS-1 – 2023
Statement 1: Quicklime (CaO) is used for white-washing of walls. While quicklime is the starting material, it is typically slaked with water to form calcium hydroxide (slaked lime) before being applied for whitewashing. So, this statement is not strictly accurate as CaO itself is not directly applied.
Statement 2: The solution of slaked lime (Ca(OH)₂) is used for whitewashing of walls. Correct. A suspension or solution of calcium hydroxide (slaked lime) is the material commonly applied as whitewash.
Statement 3: CaO reacts slowly with CO₂ in air to form a thin layer of CaCO₃ on walls. Incorrect. It is calcium hydroxide (slaked lime, Ca(OH)₂) that reacts with carbon dioxide in the air over time to form calcium carbonate (CaCO₃), which hardens and gives a shiny finish to the whitewash. CaO itself reacts readily with CO₂, but the reaction relevant to the setting of whitewash is between Ca(OH)₂ and CO₂.
Statement 4: Calcium hydroxide called ‘slaked lime’ is an inorganic compound. Correct. Calcium hydroxide is a compound of calcium, oxygen, and hydrogen, without carbon-hydrogen bonds, classifying it as an inorganic compound.
Based on the analysis, statements 2 and 4 are correct, and statements 1 and 3 are incorrect or less accurate.