Lesson 5 of 5
Plan a fair rate investigation
A plan must say how the measurements will support a conclusion.
O-Level 6092 (2026) / SEC G3 K324 (2027)
Pure onlyI can design rate investigations.Syllabus
Syllabus K324, 10(e). Design rate investigations
Plan a fair rate investigation
A plan must say how the measurements will support a conclusion.
- Independent variable
Prepare a range of acid concentrations by measured dilution, keeping total solution volume equal.
- Controls
Use equal magnesium masses and exposed areas, the same initial temperature and the same apparatus.
- Measurements
Record hydrogen volume at fixed times after mixing; repeat each concentration.
- Analysis
Plot volume-time curves and compare initial gradients, with units. A repeat checks reproducibility.
- Practical precautions
Keep away from ignition sources because hydrogen is flammable; use suitable eye protection and avoid a sealed vessel without a free gas outlet.
To investigate particle size instead, vary chip/powder size while holding carbonate mass and acid concentration/volume constant. Use acid in excess if you want final gas amount fixed by carbonate. A suitable method controls the variables that could give the same observed effect, not just the easiest variables to measure.
Check your understanding
A student compares hot powdered carbonate with cold carbonate chips. Can the difference in rate be put down to temperature?
Show the answer
No. Particle size changed as well, so either factor could explain it.
Two variables changed at once. To test temperature, keep the particle size the same; to test particle size, keep the temperature the same.