2023 · Q9
During white-washing of walls, slaked lime reacts slowly with carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Which of the following reactions represents this correctly?
General KnowledgeChemistry
- A$CaO (s) + CO_{2} (g) → CaCO_{3} (s)$
- B$CaO (l) + CO_{2} (g) → CaCO_{3} (s)$
- C$Ca(OH)_{2} (l) + CO_{2} (l) → CaCO_{3} (s) + H_{2}O (l)$
- D$Ca(OH)_{2} (aq) + CO_{2} (g) → CaCO_{3} (s) + H_{2}O (l)$
Explanation
Slaked lime is calcium hydroxide, Ca(OH)2, which reacts slowly with atmospheric carbon dioxide to form a thin layer of calcium carbonate: Ca(OH)2(aq) + CO2(g) -> CaCO3(s) + H2O(l). Options using CaO are wrong because whitewash uses slaked lime rather than quicklime, and carbon dioxide is a gas, not a liquid.