FRQ — Practicals and Projects

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 investigates soap foaming. Four equal soap solutions are prepared. Sodium carbonate added is

0.0\,\mathrm{g}

0.5\,\mathrm{g}

1.0\,\mathrm{g}

and

1.5\,\mathrm{g}

. Foam heights recorded are

2.1\,\mathrm{cm}

3.0\,\mathrm{cm}

3.6\,\mathrm{cm}

and

3.7\,\mathrm{cm}

Total: 4 marks

(a) Identify the independent variable. (1 mark)

(b) Identify the dependent variable. (1 mark)

(d) Why is the increase from $1.0\,\mathrm{g}$ to $1.5\,\mathrm{g}$ not strong evidence for a large extra effect? (1 mark)

Your response (optional — you can also work on paper)

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