#110
Measuring rates (mass loss, gas volume, graphs)
Paper 2 · Higher combined
Key steps (method)
- Decide what you can measure easily:
- Mass loss when gas escapes.
- Gas volume using a gas syringe / inverted cylinder.
- Record values at regular intervals.
- If asked for rate from a graph:
- Average rate = overall change ÷ overall time.
- Instantaneous rate = gradient of a tangent at a point.
Common mistakes
- Not taking a tangent for instantaneous rate.
- Using the wrong axis units.
- Forgetting to start timing consistently (mixing delay).
Exam-style questions (quick)
- Explain why the mass decreases during a reaction producing CO₂.
- Describe how you would measure the rate when gas is produced.
- Calculate a gradient from a rate graph.