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Learn0620Papers 5, 6 · Practical Test or Alternative to PracticalPractical skillsPractical skills in chemistry
Practical skills · Subtopic 1 of 1

Practical Skills in Chemistry

A fair test changes one independent variable, measures the dependent variable, and keeps control variables the same. Record readings in a table with units in the headings and consistent precision (burette readings to 0.05 cm30.05\ \mathrm{cm^3}). Repeat titrations until concordant (within 0.10 cm30.10\ \mathrm{cm^3}) and average only those. Accuracy is closeness to the true value; precision is closeness of repeats. Evaluate by identifying errors and suggesting specific improvements.

Cambridge 5070 Paper 3Cambridge 5070 Paper 4Cambridge 0620 Papers 5, 6Edexcel 4CH1 Paper 1CEdexcel 4CH1 Paper 2C≈ 40 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Identify independent, dependent and control variables.
  • Record and process data, including titration results.
  • Distinguish accuracy and precision; identify errors and improvements.
Pause and think

Two students measure the same titration: one gets 24.10, 24.15, 24.10 cm³; the other 23.5, 25.0, 24.2 cm³. Whose results are more precise?

Section 2 of 14

Core idea

Start hereResults you can trust

Two labs test the same medicine and get different results. Who's right? Good practical technique, careful recording and honest evaluation decide.

The big idea

Control variables to make a fair test, record data precisely, repeat to check reliability, and evaluate errors with specific improvements.

1. Planning

Variables in a fair test

Change one thing, measure one thing.

2. Titration technique

Worked exampleProcessing titration results

Rough 23.6; then 23.15, 23.30, 23.10, 23.20 cm³.

Goal
Mean titre.
Strategy
Use concordant results (within 0.10).
  1. 23.15, 23.10, 23.2023.15,\ 23.10,\ 23.20
    These are within 0.10 cm³; 23.30 is outside the range of the others.
  2. 23.15+23.10+23.203=23.15\frac{23.15+23.10+23.20}{3}=23.15
    Mean of concordant titres.
Answer23.15 cm323.15\ \mathrm{cm^3}
✓ CheckRough titre excluded ✓.

3. Evaluating

  • Random error: unpredictable scatter; reduce by repeating.
  • Systematic error: same direction each time (e.g. heat loss, zero error); fix with better method.
  • Accuracy: close to true value. Precision: repeats agree.
Exam tipGood improvements "Use a lid and insulate the cup to reduce heat loss"; "use a gas syringe to avoid gas dissolving in water"; "use a burette instead of a measuring cylinder".
Pause and think

Can results be precise but not accurate?

Summary

  • Independent, dependent, control.
  • Burette to 0.05 cm³; concordant within 0.10.
  • Specific improvements.
Key words
Concordant
Results that agree within 0.10 cm³.
Systematic error
An error that shifts all readings in the same direction.
Anomalous result
A result that does not fit the pattern.
HistoryGay-Lussac's burette. Joseph Gay-Lussac designed an early burette in 1824; its accuracy made volumetric analysis, still used daily in labs, possible.
Fun factThe colour of a drop. One drop from a burette is about 0.05 cm30.05\ \mathrm{cm^3}, which is why burette readings are recorded to the nearest 0.05 cm30.05\ \mathrm{cm^3}.
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