A sample gives a gas that turns lime water milky. On passing excess gas, the milkiness disappears. Which two calcium compounds form in order?
Answer and explanation
Correct answer: Calcium carbonate then calcium hydrogen carbonate
The governing test is the limewater reaction with carbon dioxide. First, CO2 reacts with calcium hydroxide: Ca(OH)2 + CO2 → CaCO3 + H2O. Insoluble calcium carbonate forms the milky appearance. When excess CO2 is passed, it reacts further: CaCO3 + CO2 + H2O → Ca(HCO3)2. Calcium hydrogen carbonate is soluble, so the milkiness disappears. Thus option A gives the compounds in the correct order.
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 test is the limewater reaction with carbon dioxide. First, CO2 reacts with calcium hydroxide: Ca(OH)2 + CO2 → CaCO3 + H2O. Insoluble calcium carbonate forms the milky appearance. When excess CO2 is passed, it reacts further: CaCO3 + CO2 + H2O → Ca(HCO3)2. Calcium hydrogen carbonate is soluble, so the milkiness disappears. Thus option A gives the compounds in the correct order.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Carbon and its Compounds.
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