Case study·Standard multi-step (3/5)·No calculator
Difficulty guide
The label describes the problem, not your ability.
1/5 - Foundational
Warm-up setup; checks one basic idea.
2/5 - Routine exam skill
Normal syllabus skill; usually one main rule or interpretation.
3/5 - Standard multi-step
Exam-style problem with multiple steps or a common trap.
4/5 - Hard exam skill
High-end exam problem; combines methods carefully.
5/5 - Challenge
Stretch problem beyond normal exam pressure.
Question
The figure shows a reaction carried out in a closed flask placed on a balance before and after the reaction.
Total: 5 marks
(a) State the law being tested. (1 mark)
(b) Predict whether the balance reading should change in a properly closed flask. Justify. (2 marks)
(c) Why might an open flask give a different reading in a gas-evolution reaction? (2 marks)
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