Case study·Standard multi-step (3/5)·Calculator allowed
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
A student prepares standard sodium carbonate solution and titrates it against hydrochloric acid using methyl orange. The endpoint is overshot to a deep red colour in the first trial.
Total: 3 marks
(a) Why should the first overshot trial not be used as the final titre? (1 mark)
(b) What colour change should be approached carefully with methyl orange for acid in burette and carbonate in flask? (1 mark)
(c) Why is a standard flask used in preparing the sodium carbonate solution? (1 mark)
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