Paper 5 Planning, Analysis and Evaluation
- Syllabus
- 9701–2028–2029
- Topic
- —
- Level
- A2
Learning objectives
P5.1Defining the experimental problemIdentify a safe and efficient procedure, steps, suitable apparatus, risks, independent variable, dependent variable, controlled variables, aim and prediction in words or as a predicted graph.P5.2Planning methods and apparatusDescribe the full method, apparatus arrangement, labelled diagrams, measuring instruments, volumes, concentrations, risk precautions, variation of independent variable, measurement of dependent variable, controls, result tables and how data will be used to reach a conclusion.P5.3Standard laboratory practice in plansUse standard quantitative practice such as making standard solutions, weighing by difference, achieving titration concordancy, heating to constant mass and taking extra readings near an inflection point.P5.4Dealing with dataIdentify calculations and presentation needed to draw conclusions; calculate mean, percentage, percentage gain or loss, percentage error and quantities from raw data; plot graphs, find y = mx + c values, choose axes and use correct significant figures.P5.5Conclusions from experimental evidenceDraw conclusions with detailed key features of data and analysis; judge whether data support the conclusion or prediction; give scientific explanations; make further predictions and suggest improvements.P5.6Evaluation, reliability, validity and confidenceIdentify anomalies and possible explanations; judge replication, data range, variable control and method weaknesses; explain effects of concentration or condition changes and apparatus misuse; judge reliability, trustworthiness, quality of data, validity and confidence in conclusions.
Define the experimental problem before choosing a procedure
State the aim and testable prediction, identify independent/dependent variables, specify controls, choose a feasible range and decide what measured outcome will test the relationship.
For concentration versus initial rate, vary concentration across a useful range, calculate a time-based initial rate, keep temperature and total volume constant, and sketch or state the predicted relationship.
'Investigate the effect of X' is incomplete until the dependent measurement, controls, range and predicted direction/shape are stated.
Write a complete plan from apparatus through analysis and risk control
Specify apparatus and labelled arrangement, quantities/concentrations, sequence, independent/dependent/control variables, measurement intervals/range/repeats, hazards and controls, raw-results table, calculation and graph/conclusion method.
For rate versus concentration, choose gas syringe or mass loss, constant temperature/total volume, several concentrations, repeats, timed readings and an initial-gradient rate calculation.
An apparatus list is not a reproducible plan. State what changes, what is measured, how controls are maintained and how the resulting data answer the aim.
Use standard quantitative techniques with their acceptance criteria
| Technique | Purpose/criterion |
|---|---|
| prepare standard solution | known concentration from accurate mass/volume transfer |
| weigh by difference | account for mass actually transferred |
| titrate | rough endpoint then concordant accurate titres |
| heat to constant mass | confirm no further mass change |
| extra readings near sharp change | locate an inflection/transition accurately |
Repeating an inconsistent technique does not make it valid. Apply the technique-specific transfer, concordance, constant-mass or point-density criterion.
Process raw data with the calculation or graph the question requires
Keep raw and processed data separate. Choose means for repeats, percentage change/error for comparisons, gradients for rates, or m and c from y = mx + c; show substitution/units and use justified significant figures after completing the calculation.
% change=originalnew−original×100
A correct calculator operation can still answer the wrong question. Identify whether the required evidence is a mean, percentage, gradient, intercept or derived chemical quantity before calculating.
Build conclusions from quantified evidence, theory and limitations
State the observed relationship with values/range, decide whether it supports the prediction, explain it with chemistry, then qualify the claim using scatter, anomalies, uncertainty and range. Further predictions must follow from the proposed explanation.
Rate rose across 0.10-0.50 mol dm-3, consistent with increased collision frequency; scatter at the highest concentration limits confidence there and justifies targeted repeats.
Restating the hypothesis is not a conclusion. The actual data feature, scientific explanation and confidence limit must all be present.
Evaluate reliability, validity and confidence as separate claims
| Claim | Evidence/question |
|---|---|
| reliability | are readings repeatable and adequately replicated? |
| validity | does the method measure the intended relationship with variables controlled? |
| confidence | do range, scatter, anomalies and uncertainty strongly support the conclusion? |
For each weakness, state its likely effect/direction and a specific improvement. Repeats reduce random scatter but do not repair a biased instrument, contaminated standard or invalid dependent measurement.
Agreement alone cannot prove accuracy or validity. Three concordant titres may all be systematically wrong if the standard solution is contaminated.