Long answer·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
A cleaning powder label says: "Contains sodium hydrogen carbonate. Reacts with acids to release a gas. Mildly basic."
Total: 5 marks
(a) Write the formula of sodium hydrogen carbonate. (1 mark)
(b) Write a balanced equation for its reaction with dilute hydrochloric acid. (2 marks)
(c) How can the gas be confirmed? (1 mark)
(d) Why is it safer to call the powder mildly basic rather than strongly basic? (1 mark)
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