Question detail
Calcium carbonate is heated in an open test tube and carbon dioxide escapes. Why might the measured mass appear to decrease?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations
Question
- A. Gas leaves the apparatus, so the measured sample loses mass even though atoms are conserved overall.
- B. Atoms are destroyed during heating, so the total mass of matter is reduced.
- C. The solid becomes lighter because products always have less mass than reactants.
- D. Mass conservation does not apply to reactions that make gases.
Answer
The correct option is: gas leaves the apparatus, so the measured sample loses mass even though atoms are conserved overall. This answer should be checked against the named quantitative relationship, the balanced equation where relevant, and the final unit required by the question.
Explanation
This example is different from a closed-system mass balance. If carbon dioxide escapes from an open test tube, the balance no longer measures all products, so the measured mass can fall. Conservation of mass still applies to the full reaction; the apparent loss is caused by gas leaving the apparatus.
Common mistake
Mass Misunderstanding
Students often think that the mass of products can differ from the mass of reactants in a chemical reaction.
Emphasize that according to the law of conservation of mass, the total mass of reactants must equal the total mass of products in a closed system.
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