Topic 4 of 8
Measurements and recording
Keep raw readings, temperature changes and observations interpretable.
O-Level 6092 (2026) / SEC G3 K324 (2027)
Record measurements that another person can interpret
Use the instrument scale, a clear table and observations that preserve the sequence.
Choose apparatus for the needed measurement: a volumetric pipette delivers a fixed accurate volume, a burette delivers a variable accurately measured volume, a measuring cylinder is suitable for less exact volume work, and a balance measures mass. Read the scale at eye level to avoid parallax; use the bottom of the meniscus for a clear aqueous solution unless the instructions specify otherwise.
| Trial | Initial burette / cm3 | Final burette / cm3 | Titre / cm3 |
|---|---|---|---|
| Rough | 0.00 | 24.80 | 24.80 |
| 1 | 1.10 | 25.50 | 24.40 |
| 2 | 0.20 | 24.65 | 24.45 |
| 3 | 0.30 | 24.70 | 24.40 |
For Secondary Chemistry, the syllabus normally expects burette readings to the nearest 0.05 cm3, and sufficient titrations to obtain, for a good end-point, two titres within 0.20 cm3. Record both readings and the difference. Follow the question if it gives a particular agreement criterion; do not include the rough titre in a precise mean.
Worked example
Select a justified mean titre
Use the precise titrations in the table; their maximum separation is 0.05 cm3.
- Trials 1, 2 and 3 form a close group. The rough trial was for locating the end-point.
- Mean = (24.40 + 24.45 + 24.40) / 3 = 24.4166... cm3.
- Record a suitable rounded mean of 24.42 cm3; retain the unrounded value through subsequent calculations where useful.
24.42 cm3, with the selected trials clearly identified.
Separate raw observations from interpretation. "A white precipitate forms after three drops and dissolves in excess" preserves information that "positive test" loses. Record colour, physical state, changes on standing or warming, and any confirmed gas test. Put units in table headings; do not attach a unit to a pure ratio.
Check your understandingThe initial reading is 2.35 cm3 and the final reading is 26.70 cm3. What volume was delivered?Think it through, then reveal the answer
Measure temperature changes and changes in mass
Distinguish a reading from the chemical quantity it represents.
For a temperature-change experiment, measure a stable starting temperature, combine the stated quantities, stir consistently and follow temperature with time. Use a suitable thermometer or probe, keeping it immersed appropriately without resting on the vessel. A lid and insulation reduce exchange with the surroundings. Do not treat a single late reading as the maximum change if the mixture has already cooled.
A temperature rise indicates energy transferred to the measured surroundings in an exothermic process; a fall indicates an endothermic process under comparable conditions. To compare reactions fairly, account for the amounts reacting and the mass being warmed, rather than ranking enthalpy changes by temperature rise alone.