Topic 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 onlyPlan 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.