A dilute acid is added to a white solid and the gas turns lime water milky. If excess gas removes the milkiness, which sequence is correct?
Answer and explanation
Correct answer: Calcium carbonate then calcium hydrogen carbonate
The governing reaction is the test for carbon dioxide. Carbon dioxide first reacts with lime water, Ca(OH)₂, to form insoluble calcium carbonate, CaCO₃, which makes the solution milky. When excess CO₂ is passed, the precipitate reacts further with water and carbon dioxide to form soluble calcium hydrogen carbonate, Ca(HCO₃)₂, so the milkiness disappears. Hence the correct sequence is carbonate followed by hydrogen carbonate.
Frequently asked questions
What is the correct answer to this question?
Calcium carbonate then calcium hydrogen carbonate
Why is this the correct answer?
The governing reaction is the test for carbon dioxide. Carbon dioxide first reacts with lime water, Ca(OH)₂, to form insoluble calcium carbonate, CaCO₃, which makes the solution milky. When excess CO₂ is passed, the precipitate reacts further with water and carbon dioxide to form soluble calcium hydrogen carbonate, Ca(HCO₃)₂, so the milkiness disappears. Hence the correct sequence is carbonate followed by hydrogen carbonate.
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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