An acid reacts with a metal carbonate to give a gas. Why can the milkiness disappear when that gas is passed through lime water for a long time?
Answer and explanation
Correct answer: Due to formation of soluble calcium hydrogen carbonate
The gas released from an acid–metal carbonate reaction is carbon dioxide. Initially, CO₂ reacts with calcium hydroxide in lime water: CO₂ + Ca(OH)₂ → CaCO₃ + H₂O, and insoluble calcium carbonate makes the solution milky. With excess CO₂, the precipitate reacts further: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂, which is soluble, so the milkiness disappears.
Frequently asked questions
What is the correct answer to this question?
Due to formation of soluble calcium hydrogen carbonate
Why is this the correct answer?
The gas released from an acid–metal carbonate reaction is carbon dioxide. Initially, CO₂ reacts with calcium hydroxide in lime water: CO₂ + Ca(OH)₂ → CaCO₃ + H₂O, and insoluble calcium carbonate makes the solution milky. With excess CO₂, the precipitate reacts further: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂, which is soluble, so the milkiness disappears.
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.
