Why can milky lime water become clear again when excess carbon dioxide is passed through it?
Answer and explanation
Correct answer: Due to formation of soluble calcium hydrogen carbonate
When carbon dioxide is first passed through limewater, insoluble calcium carbonate forms and causes milkiness: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. If excess CO₂ is bubbled through, the calcium carbonate reacts further with carbon dioxide and water to form soluble calcium hydrogen carbonate: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. The precipitate dissolves, so option A is correct.
Frequently asked questions
What is the correct answer to this question?
Due to formation of soluble calcium hydrogen carbonate
Why is this the correct answer?
When carbon dioxide is first passed through limewater, insoluble calcium carbonate forms and causes milkiness: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. If excess CO₂ is bubbled through, the calcium carbonate reacts further with carbon dioxide and water to form soluble calcium hydrogen carbonate: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. The precipitate dissolves, 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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