Planning Experiments
How to plan experiments for IGCSE Chemistry 0620 Paper 5 and 6 including identifying variables, writing methods, and control experiments.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Why this skill matters
Planning is the central skill tested on Paper 5 and appears in the planning section of Paper 6. A planning question typically carries 6-10 marks and asks you to design a complete experiment from scratch. Examiners look for logical structure, specific quantities, correct apparatus, and fair testing.
Method and technique
Step 1: Identify the variables
Before writing any method, clearly state:
- Independent variable: What will you change? (e.g., temperature, concentration, surface area)
- Dependent variable: What will you measure? (e.g., time taken, volume of gas, temperature change)
- Control variables: What will you keep constant? (e.g., volume of acid, mass of solid, same equipment)
Step 2: Choose the apparatus
Select apparatus appropriate for the measurements:
- Volume: measuring cylinder (approximate), burette or pipette (precise)
- Temperature: thermometer with suitable range
- Mass: balance with appropriate precision
- Time: stopwatch or stopclock
- Gas volume: gas syringe or collection over water
Name the specific apparatus and justify your choice if the question asks.
Step 3: Write the method
Write a step-by-step method using numbered points. Include:
- Specific quantities (volumes, masses, concentrations, temperatures)
- How you will vary the independent variable (e.g., “repeat using concentrations of 0.5, 1.0, 1.5, 2.0, and 2.5 mol/dm3”)
- How you will measure the dependent variable (what, when, how)
- How you will control the control variables
- How many repeats you will do (at least 2 repeats per condition for reliability)
- Safety precautions relevant to the chemicals or apparatus used
Step 4: Results and analysis
State how you will record and process the results:
- Describe the results table (what columns, what headings)
- State what graph you will plot (independent variable on x-axis, dependent on y-axis)
- Explain what pattern you expect or how you will use the data to answer the question
Common errors and how to avoid them
Vague quantities: “Add some acid” earns no marks. “Add 20 cm3 of 1.0 mol/dm3 HCl” earns them. Be specific.
Missing control variables: If you change temperature but do not keep concentration constant, the experiment is not fair. List every variable that must stay the same.
No repeats: A single measurement is unreliable. State that you will repeat each condition at least twice and calculate a mean.
Inappropriate apparatus: Using a beaker to measure 25 cm3 of solution is inaccurate. A measuring cylinder or pipette is better. Match the apparatus to the precision needed.
Forgetting safety: If the experiment involves acids, flames, or toxic gases, state the relevant precautions (safety glasses, fume cupboard, water bath for flammable substances).
Marking points examiners look for
- Independent, dependent, and control variables correctly identified
- Specific quantities and concentrations stated
- Appropriate apparatus named and justified
- Logical, step-by-step method that could be followed
- At least 5 values for the independent variable (enough data points for a graph)
- Repeats stated for reliability
- Relevant safety precautions included
- Results table or graph description included
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