A student added acid to sodium carbonate. A gas was released and lime water turned milky. Which gas was it?
Answer and explanation
Correct answer: Carbon dioxide
The governing concept is the acid–carbonate reaction. An acid reacts with sodium carbonate to form a salt, water, and carbon dioxide: 2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂. Passing the released gas through limewater produces insoluble calcium carbonate, making the limewater milky. This confirms carbon dioxide. Hydrogen would give a pop sound, while oxygen relights a glowing splint; nitrogen has no such limewater test. Therefore D is correct.
Frequently asked questions
What is the correct answer to this question?
Carbon dioxide
Why is this the correct answer?
The governing concept is the acid–carbonate reaction. An acid reacts with sodium carbonate to form a salt, water, and carbon dioxide: 2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂. Passing the released gas through limewater produces insoluble calcium carbonate, making the limewater milky. This confirms carbon dioxide. Hydrogen would give a pop sound, while oxygen relights a glowing splint; nitrogen has no such limewater test. Therefore D 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.
