22.2 Experimental skills and investigations
- Syllabus
- 0610–2026–2027
- Topic
- 22.2
- Level
- —
Learning objectives
22.2.1Select and safely use techniques and apparatus• Demonstrate knowledge of how to select and safely use techniques, apparatus and materials, including following a sequence of instructions where appropriate.22.2.2Plan experiments and investigations• Plan experiments and investigations with suitable variables, methods, apparatus and safety controls.22.2.3Record observations and measurements• Make and record observations, measurements and estimates with appropriate precision and units.22.2.4Interpret and evaluate experimental data• Interpret and evaluate experimental observations and data, including patterns, anomalies and limitations.22.2.5Evaluate and improve methods• Evaluate experimental methods and suggest possible improvements.
Select and use apparatus safely and accurately
Choose a technique, apparatus and material because it fits the quantity, range and precision required; then use it in the correct sequence while controlling its hazards.
| Need | Selection and use |
|---|---|
| volume | use a suitably sized measuring cylinder, pipette or syringe; read the meniscus at eye level on a flat surface |
| mass | use a balance with suitable resolution, zero it and measure only the intended sample |
| temperature | use a thermometer and maintain conditions with a water-bath or incubator |
| time | use a stop-clock and define consistent start and end points |
| length | use a ruler with the scale close to the object and avoid parallax |
Identify the specific hazard, state the possible harm and match it to a precaution: for example, eye protection for irritant splashes, forceps or a tile for cutting, and a water-bath rather than a naked flame near flammable material.
Naming apparatus or saying ‘be careful’ is insufficient. Justify suitability and explain how the precaution reduces the named risk.
Plan a valid and safe investigation
A valid plan changes one independent variable, measures a dependent variable and controls other factors so any observed effect can be attributed to the intended change.
| Planning decision | Required detail |
|---|---|
| question and prediction | state the relationship being tested and a reasoned expected direction |
| independent variable | choose a suitable range with enough values and equal or justified intervals |
| dependent variable | state exactly what is measured, how and in which units |
| controlled variables | name each important factor, how it is kept constant and why it could affect the result |
| method and apparatus | give a reproducible sequence, quantities, timings and justified equipment |
| control | include a comparison lacking the tested factor when appropriate |
| reliability | repeat at each value, identify anomalies and calculate a mean |
| safety | link each material or procedural hazard to a suitable precaution |
| results | specify a headed table and how data will be processed or graphed |
‘Make it a fair test’ is not a plan. State operational details, and do not confuse a controlled variable with a control treatment.
Record observations and measurements correctly
A scientific record preserves what was observed or measured with enough precision, units and structure for another person to analyse it.
| Evidence | Recording rule |
|---|---|
| analogue reading | read at eye level, use the correct meniscus and estimate one digit where the scale permits |
| digital reading | record all displayed digits unless instructed otherwise |
| repeated measurements | keep raw replicates in separate columns and calculate the mean separately |
| qualitative observation | state the actual colour, appearance or change, not merely ‘positive’ |
| results table | put the independent variable first; include units once in headings, not in every cell |
| estimate or calculation | show working and report the requested significant figures |
Values measured by the same apparatus should normally use consistent decimal places. Record sufficient observations across the chosen range and never silently replace an anomalous raw result.
Precision is the resolution and consistency of recording; it does not guarantee accuracy. Units belong in headings and must match the measured quantity.
Interpret and evaluate experimental data
Interpretation extracts a relationship from observations; evaluation judges how strongly the data support it and where data quality limits the conclusion.
| Step | Evidence-based action |
|---|---|
| process | calculate means, rates or changes consistently and present a suitable graph |
| interpret | state direction, shape, range, peak or plateau and support it with values and units |
| inspect | identify anomalous points by their departure from repeats or the overall pattern |
| act | check the raw record and repeat the measurement where possible; exclude only with justification |
| conclude | answer the tested relationship within the investigated range |
| evaluate | consider spread, repeats, sample size, resolution, uncontrolled variables and whether association proves causation |
Use interpolation within the measured range and extrapolation beyond it with caution. A gradient or intercept is meaningful only when taken from an appropriate best-fit line or curve and reported with units.
Do not call every inconvenient result anomalous, and do not remove an anomaly simply to improve the trend. A conclusion must acknowledge contradictory evidence and limitations.
Improve a method by targeting its weaknesses
A useful method evaluation identifies a specific weakness, explains its effect on the evidence and proposes a feasible change that directly reduces that weakness.
| Weakness | Likely effect | Targeted improvement |
|---|---|---|
| too few repeats or small sample | low reliability; chance variation has more influence | increase repeats or sample size and calculate a mean |
| subjective endpoint | inconsistent judgement | use a colorimeter, data logger or defined endpoint where suitable |
| uncontrolled condition | confounding change in the dependent variable | monitor and keep the named factor constant |
| coarse apparatus scale | large reading uncertainty | use apparatus with finer resolution and suitable range |
| narrow or sparse independent-variable range | trend or optimum is poorly resolved | add values across the range, especially near the changing region |
| biased sampling | sample does not represent the population | use random sampling and an adequate sample size |
Write evaluations as weakness → effect → improvement. If a control is missing, add the correct control and explain which alternative cause it rules out.
‘Use better equipment’, ‘repeat’ or ‘be more accurate’ is too vague. Name what changes, how it is used and which error, validity or reliability problem it addresses.