Why can the milkiness of lime water decrease when excess carbon dioxide is passed?
Answer and explanation
Correct answer: Soluble calcium hydrogen carbonate forms
When carbon dioxide is first passed through lime water, insoluble calcium carbonate forms and makes the solution milky: Ca(OH)2 + CO2 → CaCO3 + H2O. If excess CO2 is passed, the calcium carbonate reacts further with carbon dioxide and water to form soluble calcium hydrogen carbonate: CaCO3 + CO2 + H2O → Ca(HCO3)2. Because the precipitate dissolves, the milkiness decreases. The other options do not explain this observation.
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What is the correct answer to this question?
Soluble calcium hydrogen carbonate forms
Why is this the correct answer?
When carbon dioxide is first passed through lime water, insoluble calcium carbonate forms and makes the solution milky: Ca(OH)2 + CO2 → CaCO3 + H2O. If excess CO2 is passed, the calcium carbonate reacts further with carbon dioxide and water to form soluble calcium hydrogen carbonate: CaCO3 + CO2 + H2O → Ca(HCO3)2. Because the precipitate dissolves, the milkiness decreases. The other options do not explain this observation.
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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