Topic 1 of 6
Choose a measurement that answers the question
Apparatus choice depends on range, precision and what changes.
O-Level 6092 (2026) / SEC G3 K324 (2027)
Choose a measurement that answers the question
Apparatus choice depends on range, precision and what changes.
| Quantity or task | Apparatus | Reason |
|---|---|---|
| Time | Stopwatch | Measure an interval; define exactly when timing starts and ends. |
| Temperature | Thermometer or temperature probe | Measure the reaction mixture, not the hot container wall. |
| Mass | Balance | Measure mass directly; subtract the container mass. |
| Approximate liquid volume | Measuring cylinder | Quick measurement where modest precision is sufficient. |
| One accurate fixed volume | Volumetric pipette and filler | Delivers its calibrated volume, such as 25.0 cm3. |
| Accurate variable volume | Burette | Volume delivered = final minus initial reading. |
| Gas volume | Gas syringe | Collect gas directly and read the change in volume. |
Read a liquid meniscus at eye level to avoid parallax; for a clear aqueous solution read its bottom. Record units and precision consistently. A larger container is not automatically more accurate. A pipette supplies one fixed volume; a burette is appropriate when the required volume is found during a titration.
Worked example
Measure a rate rather than an endpoint
Compare how magnesium reacts with two acid concentrations.
- Use equal masses and surface areas of magnesium, equal acid volumes and the same initial temperature.
- Collect hydrogen in an airtight gas-syringe setup and record volume at regular times.
- Compare initial gradients or the time to reach the same selected volume; repeat to assess consistency.
Answer
Gas volume against time reveals rate. Final gas volume alone may be identical despite different rates.
Check your understandingA burette reads 1.20 cm3 initially and 23.65 cm3 finally. What volume was delivered?Think it through, then reveal the answer
23.65 - 1.20 = 22.45 cm3. The final reading is not itself the delivered volume unless the initial reading was zero.