A white powder releases heat when mixed with water and forms a milky solution. Passing carbon dioxide through this solution gives a white precipitate. What can the powder be?
Answer and explanation
Correct answer: Quicklime
Quicklime is calcium oxide. It reacts vigorously with water to form slaked lime and release heat: CaO + H₂O → Ca(OH)₂. The resulting limewater becomes milky when carbon dioxide is passed through it because insoluble calcium carbonate forms: Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O. The combined observations identify quicklime, so option A is correct.
Frequently asked questions
What is the correct answer to this question?
Quicklime
Why is this the correct answer?
Quicklime is calcium oxide. It reacts vigorously with water to form slaked lime and release heat: CaO + H₂O → Ca(OH)₂. The resulting limewater becomes milky when carbon dioxide is passed through it because insoluble calcium carbonate forms: Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O. The combined observations identify quicklime, so option A is correct.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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