A gas produced by adding dilute hydrochloric acid to sodium carbonate solution is passed through limewater. Why does limewater first turn milky and then become clear when excess gas is passed?
Answer and explanation
Correct answer: Calcium carbonate forms first and then calcium hydrogen carbonate forms
Hydrochloric acid reacts with sodium carbonate and releases carbon dioxide: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂. Initially, CO₂ reacts with limewater to form insoluble calcium carbonate, CaCO₃, which makes it milky. With excess CO₂, this precipitate reacts with water to form soluble calcium hydrogen carbonate, Ca(HCO₃)₂, so the solution clears. Thus A is correct.
Frequently asked questions
What is the correct answer to this question?
Calcium carbonate forms first and then calcium hydrogen carbonate forms
Why is this the correct answer?
Hydrochloric acid reacts with sodium carbonate and releases carbon dioxide: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂. Initially, CO₂ reacts with limewater to form insoluble calcium carbonate, CaCO₃, which makes it milky. With excess CO₂, this precipitate reacts with water to form soluble calcium hydrogen carbonate, Ca(HCO₃)₂, so the solution clears. Thus 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.
