If dilute acid is added to an unknown solid and the evolved gas turns lime water milky, which ion is likely present in the solid?
Answer and explanation
Correct answer: Carbonate ion
Limewater turns milky when carbon dioxide is passed through it, because insoluble calcium carbonate forms: CO2 + Ca(OH)2 → CaCO3 + H2O. Dilute acids react with carbonate ions to release carbon dioxide, for example CO3^2− + 2H+ → CO2 + H2O. Therefore carbonate is the likely ion; chloride and nitrate do not normally give this gas test.
Frequently asked questions
What is the correct answer to this question?
Carbonate ion
Why is this the correct answer?
Limewater turns milky when carbon dioxide is passed through it, because insoluble calcium carbonate forms: CO2 + Ca(OH)2 → CaCO3 + H2O. Dilute acids react with carbonate ions to release carbon dioxide, for example CO3^2− + 2H+ → CO2 + H2O. Therefore carbonate is the likely ion; chloride and nitrate do not normally give this gas test.
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.
