Why does the milkiness of lime water disappear when excess carbon dioxide is passed?
Answer and explanation
Correct answer: Soluble calcium hydrogen carbonate forms
Initially, carbon dioxide reacts with limewater, calcium hydroxide, to form insoluble calcium carbonate: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. The suspended CaCO₃ causes milkiness. When excess CO₂ is passed, the precipitate reacts further with water and carbon dioxide to form soluble calcium hydrogen carbonate: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. The solid dissolves, so the milkiness disappears and option A is correct.
Frequently asked questions
What is the correct answer to this question?
Soluble calcium hydrogen carbonate forms
Why is this the correct answer?
Initially, carbon dioxide reacts with limewater, calcium hydroxide, to form insoluble calcium carbonate: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. The suspended CaCO₃ causes milkiness. When excess CO₂ is passed, the precipitate reacts further with water and carbon dioxide to form soluble calcium hydrogen carbonate: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. The solid dissolves, so the milkiness disappears and 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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