What practical skills are assessed in Unit 4, and how do you plan, record and evaluate an experiment well?
An overview of Unit 4 Practical Skills: the nine prescribed practicals across biology, chemistry and physics, planning with variables, recording results in tables and graphs, and evaluating accuracy, precision and sources of error.
A concise overview of Unit 4 Practical Skills in CCEA GCSE Single Award Science, covering the nine prescribed practicals, planning with variables, recording results in tables and graphs, and evaluating accuracy, precision and sources of error.
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What this dot point is asking
CCEA assesses your practical skills in Unit 4. This page is a concise overview: the prescribed practicals, how to plan an experiment with variables, how to record and present results, and how to evaluate accuracy and sources of error. It is a skills unit, not a body of facts to learn, so the focus is on doing science well.
The prescribed practicals
These appear throughout Units 1 to 3 as practical contexts, and Unit 4 assesses your ability to plan, carry out and evaluate them.
Planning: variables and a fair test
A good plan also chooses a sensible range and interval for the independent variable, repeats readings to spot anomalies, and identifies the equipment needed and any safety precautions.
Recording and presenting results
Evaluating: accuracy, precision and errors
Repeating readings and taking a mean reduces the effect of random errors. A good evaluation names a specific source of error and suggests a realistic improvement.
Examples in context
Example 1. Why repeats and a mean matter. A single reading can be thrown off by a random error, such as starting a stopwatch a moment late. Taking several readings and a mean smooths out this scatter and reveals any anomaly that should be ignored. This is why CCEA practical work rewards repeated measurements: they improve the reliability of the result without changing the method.
Example 2. Spotting a systematic error. If a top-pan balance reads 0.2 g with nothing on it, every mass recorded is 0.2 g too high, a systematic error that repeating will not fix. Zeroing the balance first removes it. Recognising that a systematic error shifts all readings the same way, while a random error scatters them, is a key evaluation skill assessed in Unit 4.
Try this
Q1. In an experiment, what name is given to the variable you deliberately change? [1 mark]
- Cue. The independent variable.
Q2. State one way to reduce the effect of random errors in an experiment. [1 mark]
- Cue. Repeat the readings and take a mean (and ignore anomalies).
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA SAS 20203 marksIn an experiment to investigate how temperature affects the rate of a reaction, name the independent, dependent and one control variable.Show worked answer →
Three marks, one for each variable correctly identified.
Independent variable: the temperature, because that is the one you deliberately change.
Dependent variable: the rate of reaction (for example the time taken or the volume of gas per minute), because that is what you measure.
Control variable (any one): the concentration of the reactant, the volume of the solution, or the mass of the solid. These are kept the same so the test is fair.
Markers reward the changed variable as independent, the measured variable as dependent, and a sensible variable kept constant.
CCEA SAS 20194 marksA student measures the energy released by a burning fuel but gets a value lower than the true one. Suggest two sources of error and one improvement.Show worked answer →
Four marks: two sources of error, one improvement, and a clear link.
Source 1: heat is lost to the surroundings (the air and the container), so less energy reaches the water and the measured value is too low.
Source 2: not all of the fuel burns completely, or some evaporates, so less energy is released than expected.
Improvement: use a screen or shield around the apparatus to reduce heat loss to the surroundings (or insulate the container).
This raises the measured energy closer to the true value. Markers reward two valid sources of error and a sensible improvement that addresses one of them.
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Sources & how we know this
- CCEA GCSE Science: Single Award specification — CCEA (2017)