A student heated calcium carbonate in an open test tube. The mass of the solid decreased after heating, so the student concluded that the law of conservation of mass is incorrect. What is the correct correction to this conclusion?
Answer and explanation
Correct answer: Carbon dioxide gas escaped; in a closed system, the total mass remains unchanged.
Calcium carbonate undergoes thermal decomposition: CaCO₃ → CaO + CO₂. In the open test tube, carbon dioxide escapes, so the measured solid loses the mass of the gas and appears lighter. For example, 100 g of calcium carbonate can produce 56 g of calcium oxide and 44 g of carbon dioxide; the total remains 100 g when all products are included. Calcium atoms are not destroyed, and CO₂ has mass. Therefore option A correctly explains the observation.
Frequently asked questions
What is the correct answer to this question?
Carbon dioxide gas escaped; in a closed system, the total mass remains unchanged.
Why is this the correct answer?
Calcium carbonate undergoes thermal decomposition: CaCO₃ → CaO + CO₂. In the open test tube, carbon dioxide escapes, so the measured solid loses the mass of the gas and appears lighter. For example, 100 g of calcium carbonate can produce 56 g of calcium oxide and 44 g of carbon dioxide; the total remains 100 g when all products are included. Calcium atoms are not destroyed, and CO₂ has mass. Therefore option A correctly explains the observation.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Chemical Reactions and Equations.
