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Detailed notes on Experimental Techniques for Cambridge IGCSE Coordinated Science, covering key concepts, explanations, examples, and exam-focused revision points.
Accurate measurement underpins all chemistry practicals. Cambridge Paper 6 tests your ability to record measurements correctly, identify sources of error, and suggest improvements to experimental procedures.
Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).
Choosing the right apparatus is the first step to accurate measurements.
| Measurement | Apparatus | Notes |
|---|---|---|
| Volume of liquid | Measuring cylinder | Read from bottom of meniscus at eye level |
| Accurate volume | Graduated pipette or burette | More precise; used in titrations |
| Volume of gas | Gas syringe or inverted measuring cylinder over water | |
| Mass | Balance (electronic) | Zero before use (tare); record to 2 d.p. if balance reads to 0.01 g |
| Temperature | Thermometer | Read at eye level; wait until stable |
| Time | Stopwatch | Start/stop at defined moment consistently |
| Concentration | Calculated from moles and volume | c = n/V |
Meniscus: water and most aqueous solutions form a concave meniscus — read from the BOTTOM of the curve. Mercury forms a convex meniscus — read from the TOP.
Parallax error: occurs when eye is not level with the scale markings. Always read at eye level to avoid overestimating or underestimating.
Burette: used in titrations to deliver variable, precise volumes. Read to 0.05 cm³ (half the smallest division). Record both initial and final readings; titre = final − initial.
Every experiment has errors — identify whether they are random or systematic, and suggest specific improvements.
Systematic errors: constant, in one direction — caused by faulty apparatus or poor technique. Example: balance not zeroed → all readings too high.
Random errors: unpredictable variation — caused by difficulty of judgment (timing, reading a scale). Example: reaction timing with a stopwatch.
Anomalous results (outliers): Results significantly different from others — often due to a specific error (e.g. spilling a sample, misreading). Identify and exclude from mean calculation. State why it was excluded.
Improving experimental design:
Percentage uncertainty: uncertainty / measurement × 100%. Example: reading a thermometer with uncertainty ±0.5°C at 25.0°C → 0.5/25.0 × 100% = 2%.
Verbatim phrases and definitions Cambridge mark schemes credit.
Paper 6: 'Describe how you would accurately measure 25.0 cm³ of solution' (2 marks — pipette or burette, read at eye level, meniscus). 'Identify one source of error in this experiment and suggest how to reduce it' (2 marks). Data analysis: 'Identify the anomalous result and explain how you should deal with it' (2 marks — state the anomalous value, exclude from mean calculation). Results tables must include units in the header and values to consistent decimal places.
Sources: Cambridge IGCSE Coordinated Sciences 0654 syllabus 2025-2027 (C2); 0654 Paper 6 past papers 2022-2024. Last reviewed 2026-05-14.
Step-by-step solutions to past-paper-style questions on measurement, written exactly the way a tutor would explain them at the board.
Question
A burette reads 24.85cm3. State the uncertainty in this reading and explain how many significant figures should be recorded.
Step-by-step solution
Step 1
A burette is graduated in 0.1 cm³ divisions. Readings can be estimated to ±0.05 cm³ (half the smallest division).
uncertainty=±0.05cm3
Step 2
The reading 24.85 cm³ is recorded to 4 significant figures, consistent with the precision of the burette.
Answer
The uncertainty is ±0.05cm3; the reading is recorded to 4 significant figures (24.85 cm³).
Question
A student measures the volume of a liquid as 25.0cm3 using a measuring cylinder. The actual volume is 24.5cm3. Calculate the percentage error.
Step-by-step solution
Step 1
Calculate the absolute error.
absolute error=25.0−24.5=0.5cm3
Step 2
Apply the percentage error formula.
% error=24.50.5×100=2.0%
Answer
Percentage error =2.0%
Examiner tip
Use the actual (true) value as the denominator, not the measured value.
Question
State the difference between a systematic error and a random error, and give one example of each.
Step-by-step solution
Step 1
Systematic error: a consistent offset that always shifts measurements in the same direction by roughly the same amount. Cannot be reduced by repeating measurements.
Step 2
Example of systematic error: a balance with a zero error reads 0.5 g when nothing is on it; every mass measurement is 0.5 g too high.
Step 3
Random error: unpredictable fluctuations that vary in size and direction between repeat readings.
Step 4
Example of random error: slight variation in how a student judges the meniscus in a measuring cylinder. Reduced by taking repeat readings and calculating a mean.
Answer
Systematic error: consistent offset in one direction (e.g. zero error); random error: varies between measurements (e.g. parallax); random errors are reduced by averaging repeats.
The formulae you need to memorise for measurement on the Cambridge IGCSE 0654 paper, with every variable defined in plain English and a note on when to use it.
% error=true value∣measured value−true value∣×100%
When to use
Comparing the accuracy of a measurement to the true value.
uncertainty=±2smallest division
When to use
Estimating the reading uncertainty for any analogue instrument.
Definitions to memorise and the exact keywords mark schemes credit for measurement answers — sharpened from recent examiner reports for the 2026 0654 sitting.
The degree to which repeated measurements give the same result; a measure of reproducibility. A precise instrument has a small random error.
How close a measurement is to the true value. Affected by systematic errors.
An error that consistently shifts all measurements in the same direction by the same amount, such as a zero error on a balance or parallax from always reading from the same angle.
An error that varies unpredictably between measurements; reduced (but not eliminated) by taking repeat readings and calculating a mean.
All digits that carry meaning contributing to measurement precision; the last significant figure is the first uncertain digit.
The smallest change in the quantity being measured that causes a noticeable change in the reading; equal to the smallest scale division.
The traps other students keep falling into on measurement questions — taken from recent Cambridge IGCSE 0654 examiner reports and mark schemes — and how to avoid them.
Why it happens
Students read the upper edge of water in a measuring cylinder or burette, giving a value that is too high.
How to avoid it
Always align the eye with the bottom of the meniscus at the same horizontal level when reading volume.
Why it happens
Students think a precise instrument is always accurate; the two are independent concepts.
How to avoid it
Precision = reproducibility (low random error); accuracy = closeness to true value (low systematic error). An instrument can be precise but inaccurate (consistent zero error).
0654 Examiner Report 2022
Why it happens
Students do not record all digits shown by the instrument.
How to avoid it
A burette reads to 2 decimal places; always write both decimal digits (e.g. 24.85, 25.00).
The things students keep getting wrong in this sub-topic, answered.