Long answer·Challenge (5/5)·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
Use the idea from Chemical Formulae, Masses and Laws to answer this situation: A compound is formed by aluminium ions of valency and sulphate ions of valency . What should be balanced?
Total: 4 marks
(a) Identify the concept. (1 mark)
(b) Explain the reasoning. (2 marks)
(c) Mention one common wrong answer and correct it. (1 mark)
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