Why does the milkiness disappear when excess carbon dioxide is passed through lime water?
Answer and explanation
Correct answer: Soluble calcium hydrogen carbonate is formed
The governing concept is the two-stage reaction of carbon dioxide with limewater. Initially, CO₂ reacts with calcium hydroxide to form insoluble calcium carbonate, Ca(OH)₂ + CO₂ → CaCO₃ + H₂O, causing milkiness. When excess CO₂ is bubbled through, the precipitate reacts further: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. Calcium hydrogen carbonate is soluble, so the precipitate dissolves and the solution becomes clear. Option A is correct.
Frequently asked questions
What is the correct answer to this question?
Soluble calcium hydrogen carbonate is formed
Why is this the correct answer?
The governing concept is the two-stage reaction of carbon dioxide with limewater. Initially, CO₂ reacts with calcium hydroxide to form insoluble calcium carbonate, Ca(OH)₂ + CO₂ → CaCO₃ + H₂O, causing milkiness. When excess CO₂ is bubbled through, the precipitate reacts further: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. Calcium hydrogen carbonate is soluble, so the precipitate dissolves and the solution becomes clear. 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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