A gas first turns lime water milky and removes the milkiness when passed in excess. Which soluble substance forms in excess?
Answer and explanation
Correct answer: Calcium hydrogen carbonate
The governing concept is the reaction of carbon dioxide with lime water. Carbon dioxide first reacts with calcium hydroxide to form insoluble calcium carbonate, which makes the solution milky: CO₂ + Ca(OH)₂ → CaCO₃ + H₂O. When excess CO₂ is passed, the carbonate reacts further with water and carbon dioxide to form soluble calcium hydrogen carbonate: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. Therefore, option C is correct; calcium carbonate is only the initial precipitate.
Frequently asked questions
What is the correct answer to this question?
Calcium hydrogen carbonate
Why is this the correct answer?
The governing concept is the reaction of carbon dioxide with lime water. Carbon dioxide first reacts with calcium hydroxide to form insoluble calcium carbonate, which makes the solution milky: CO₂ + Ca(OH)₂ → CaCO₃ + H₂O. When excess CO₂ is passed, the carbonate reacts further with water and carbon dioxide to form soluble calcium hydrogen carbonate: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. Therefore, option C is correct; calcium carbonate is only the initial precipitate.
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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