Lime basics used in construction chemistry: Which of the following statements about quick lime and slaked lime is/are correct?
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ASlaked lime contains calcium hydroxide
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BQuick lime contains calcium oxide
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CSlaked lime may be obtained from quick lime
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DSlaked lime is produced by adding water to quick lime
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EAll of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Lime products are central to mortars, soil stabilisation, and heritage conservation. Distinguishing between quick lime and slaked lime is fundamental for mixing, safety, and performance on site.
Given Data / Assumptions:
- Chemical names: quick lime = calcium oxide (CaO); slaked lime = calcium hydroxide (Ca(OH)2).
- Slaking is the hydration reaction of CaO with water.
Concept / Approach:Quick lime is produced by calcining limestone (CaCO3 → CaO + CO2). Adding water to quick lime (slaking) yields slaked lime (CaO + H2O → Ca(OH)2 + heat). Slaked lime is then used in mortars and putty. All listed statements are consistent with this reaction pathway and naming convention.
Step-by-Step Solution:
Check composition: slaked lime → Ca(OH)2 → correct.Quick lime → CaO → correct.Production route: slaked lime obtained by hydrating quick lime → correct.Therefore, all statements are true → choose “All of the above.”Verification / Alternative check:Standard chemistry references confirm the exothermic slaking reaction and the material designations used in construction specifications.
Why Other Options Are Wrong:Since A–D are all correct, any single-choice alternative would be incomplete; hence E is the only comprehensive correct option.
Common Pitfalls:
- Confusing “hydrated lime” with gypsum or cement.
- Underestimating the heat released during slaking, which is a safety hazard.
Final Answer:All of the above