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
During a laboratory audit, one chloroform bottle is found half-filled near a sunny window, an old carbon tetrachloride cleaner is found near a burner, and a poster mentions the historical use of DDT as an insecticide.
Total: 3 marks
(a) What is the risk with the chloroform bottle? (1 mark)
(b) Why is the carbon tetrachloride cleaner unsafe near heat? (1 mark)
(c) Why is DDT no longer treated as an ordinary harmless insecticide? (1 mark)
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