A white powder reacts with dilute acid to release a gas. The gas turns lime water milky, and excess gas reduces the milkiness. Which group can the white powder belong to?
Answer and explanation
Correct answer: Carbonate or hydrogen carbonate
The governing test is the carbonate test. Carbon dioxide turns limewater milky by forming insoluble calcium carbonate: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. When excess CO₂ is passed, soluble calcium hydrogen carbonate forms, so the milkiness disappears. Carbonates and hydrogen carbonates release CO₂ with dilute acids; ordinary chlorides, sulphates and nitrates do not give this characteristic result. Therefore option A is correct.
Frequently asked questions
What is the correct answer to this question?
Carbonate or hydrogen carbonate
Why is this the correct answer?
The governing test is the carbonate test. Carbon dioxide turns limewater milky by forming insoluble calcium carbonate: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. When excess CO₂ is passed, soluble calcium hydrogen carbonate forms, so the milkiness disappears. Carbonates and hydrogen carbonates release CO₂ with dilute acids; ordinary chlorides, sulphates and nitrates do not give this characteristic result. Therefore option A 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.
