A gas released from a carbonate sample with acid is passed into lime water for a long time. Why can the final solution become clear again?
Answer and explanation
Correct answer: Excess gas forms soluble calcium hydrogen carbonate
The gas evolved is carbon dioxide. Initially, CO₂ reacts with lime water: CO₂ + Ca(OH)₂ → CaCO₃↓ + H₂O, and insoluble calcium carbonate makes the liquid milky. When excess CO₂ is passed, the precipitate reacts further: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂, which is soluble. Thus the milkiness disappears and option B is correct.
Frequently asked questions
What is the correct answer to this question?
Excess gas forms soluble calcium hydrogen carbonate
Why is this the correct answer?
The gas evolved is carbon dioxide. Initially, CO₂ reacts with lime water: CO₂ + Ca(OH)₂ → CaCO₃↓ + H₂O, and insoluble calcium carbonate makes the liquid milky. When excess CO₂ is passed, the precipitate reacts further: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂, which is soluble. Thus the milkiness disappears and option B 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.
