Cambridge IGCSE Chemistry 0620 Paper 6: A Practical Revision Guide With Worked Examples

Does IGCSE Chemistry Paper 6 feel confusing, even when you understand the theory?

You're not alone.

Many students can explain a chemical reaction perfectly. But when the question asks them to describe an experiment, interpret a graph or identify an unknown solution, they suddenly feel unsure.

The good news? Paper 6 becomes much easier to approach once you understand how practical questions work.

You don't need to conduct an experiment in the examination. You need to understand what happens during an experiment and explain your findings clearly.

This guide walks you through the key practical skills, common question types and worked examples.

Let's make Paper 6 feel less intimidating.

Paper 6 is called Alternative to Practical. It is part of Cambridge IGCSE Chemistry (0620).

Instead of performing experiments in a laboratory during the exam, you'll answer written questions about experimental methods, observations and results.

Here are the important details for the 2026–2028 syllabus:

• Paper: 0620/6 — Alternative to Practical
• Duration: 1 hour
• Maximum marks: 40
• Contribution to final qualification: 20%
• Question format: Compulsory structured questions
• Assessment objective: AO3 — Experimental Skills and Investigations

Both Core and Extended candidates take a practical assessment. Their school or examination centre enters them for either Paper 5 or Paper 6.

Paper 5 involves performing experiments in a laboratory. Paper 6 assesses the same experimental skills through written questions.

One important thing to remember: Alternative to Practical does not mean you can skip learning practical chemistry.

You still need to understand laboratory equipment, measurement techniques, chemical reactions and experimental safety.

These requirements are set out in the official Cambridge IGCSE Chemistry 0620 syllabus for 2026–2028.

Paper 6 isn't simply a test of memorised chemical reactions.

Cambridge wants to see whether you understand how scientists investigate questions, collect evidence and reach sensible conclusions.

Focus your revision on six important areas.

1. Laboratory Apparatus and Measurements

You may be asked to identify equipment or explain why it is used.

Common apparatus includes measuring cylinders, burettes, pipettes, thermometers, balances, gas syringes and conical flasks.

The key is understanding the purpose of each instrument.

For example, a measuring cylinder is useful for measuring approximate liquid volumes. A volumetric pipette is designed to transfer a fixed volume accurately.

Revision tip: When learning an instrument's name, also learn what it measures and why it is suitable.

2. Chemical Tests and Observations

These questions test your ability to recognise substances from experimental results.

You should understand tests for gases, metal ions and non-metal ions.

For example, carbon dioxide turns limewater milky. A glowing splint relights in oxygen.

Don't just remember the name of the gas.

Remember the test and what a positive result looks like.

3. Graphs and Experimental Data

Some questions give you readings from an experiment.

You may need to plot points, draw a suitable line, calculate a gradient or explain a trend.

Accuracy matters here.

A graph with the correct idea can still lose marks if the axes are incorrectly labelled or the scale is unsuitable.

4. Separation and Purification

Make sure you're comfortable with filtration, crystallisation, chromatography and distillation.

Each method solves a different problem.

For example, filtration separates an insoluble solid from a liquid. Crystallisation helps obtain crystals of a dissolved substance.

Ask yourself: Why is this method being used rather than another?

5. Experimental Calculations

You may have to calculate temperature changes, rates of reaction or volumes used in a titration.

These are often short calculations.

But missing units, using the wrong readings or rounding too early can create avoidable mistakes.

6. Planning and Improving Experiments

These questions ask you to think like a scientist.

You may need to identify variables, choose equipment, describe a method or suggest improvements.

The strongest answers explain exactly what should be done and why.

Let's look at some examples.

Imagine a student mixes two solutions and records the following temperatures.

Initial temperature: 22.0°C

Highest temperature: 29.5°C

The question asks:

Calculate the temperature change.

Start with the formula:

Temperature change = Final temperature − Initial temperature

Substitute the values:

29.5 − 22.0 = 7.5

Answer: 7.5°C

Simple, right?

Now imagine the next question asks whether the reaction is exothermic or endothermic.

The temperature increased.

That means the reaction released energy to the surroundings.

Answer: Exothermic.

This is why you should understand the science behind every calculation, not just memorise the formula.

A Common Mistake

Some students correctly calculate 7.5 but forget the unit.

Others say the reaction is endothermic because they remember that heat is involved.

A simple habit helps: check the direction of the temperature change before deciding what it means.

Here's another common practical-skills question.

A student collects 25 cm³ of hydrogen gas in 50 seconds.

Calculate the average rate of gas production over this period.

The formula is:

Average rate = Volume of gas produced ÷ Time taken

Substitute the values:

25 ÷ 50 = 0.50

Answer: 0.50 cm³/s

Notice the unit.

We measured volume in cubic centimetres and time in seconds.

That's why the rate is expressed in cm³/s.

What If the Question Includes a Graph?

A graph might show how the volume of gas changes over time.

A steeper slope means gas is being produced more quickly.

If the curve gradually becomes flatter, the reaction is slowing down.

When the line becomes horizontal, gas production has stopped.

A question may also ask for the rate at a particular moment. In that case, you may need to draw a tangent to the curve and calculate its gradient.

Revision tip: Learn the difference between an average rate over a time interval and an instantaneous rate at one point.

Titration questions can look difficult because there are several readings and pieces of apparatus.

But the first calculation is often straightforward.

Imagine a student records:

Initial burette reading: 1.20 cm³

Final burette reading: 24.80 cm³

The question asks for the volume delivered from the burette, also called the titre.

Use:

Titre = Final burette reading − Initial burette reading

24.80 − 1.20 = 23.60

Answer: 23.60 cm³

That's it.

You may then be asked to explain how the student knows the reaction has reached its endpoint.

An appropriate indicator changes colour at the endpoint.

The exact colour change depends on which indicator and solutions are used.

How to Avoid Titration Mistakes

Pay attention to three things.

First, read the burette scale carefully. Its scale increases downwards.

Second, subtract the initial reading from the final reading.

Third, record your answer using suitable precision and the correct unit.

A small calculation error can affect everything that follows.

Qualitative analysis is about identifying substances using chemical tests.

You don't always need a complicated explanation.

You need a clear observation and a sensible conclusion.

Example: Identifying Copper(II) Ions

A student adds aqueous sodium hydroxide to an unknown solution.

A light blue precipitate forms.

What could this suggest?

Answer: The solution may contain copper(II) ions, Cu²⁺.

The important observation is the formation of a light blue precipitate.

If aqueous ammonia is added instead, copper(II) ions produce a light blue precipitate that dissolves in excess ammonia to form a dark blue solution.

This additional observation can help confirm the identification.

Important Gas Tests to Know

Here are some useful tests from the Cambridge syllabus.

Hydrogen: Produces a squeaky pop with a lighted splint.

Oxygen: Relights a glowing splint.

Carbon dioxide: Turns limewater milky.

Ammonia: Turns damp red litmus paper blue.

Chlorine: Bleaches damp litmus paper.

Sulfur dioxide: Turns acidified aqueous potassium manganate(VII) from purple to colourless.

Cambridge provides qualitative analysis notes in Paper 6.

That means you don't need to rely only on memorising every entry in a test chart.

However, understanding the tests will help you use those notes quickly and interpret the results correctly.

A useful exam habit: Describe exactly what you observe before naming the substance.

For example, write "a white precipitate forms" rather than simply "the solution changes".

Precise scientific language makes your answer clearer.

This is where many students lose confidence.

A question might say:

Plan an investigation to find out how changing the concentration of hydrochloric acid affects the rate of its reaction with magnesium.

You don't need to write a long essay.

You need a clear, logical method.

Step 1: Identify the Independent Variable

This is the factor being changed.

In this experiment, it's the concentration of hydrochloric acid.

Step 2: Identify the Dependent Variable

This is what you're measuring.

You could measure the time taken to collect a fixed volume of hydrogen gas.

For example, measure how long it takes to collect 20 cm³ of hydrogen.

Step 3: Keep Other Variables Constant

To make the test fair, keep important conditions the same.

These include:

• The mass and surface area of magnesium.
• The volume of acid.
• The starting temperature.
• The experimental apparatus.

Only the acid concentration should change deliberately.

Step 4: Describe How Results Are Collected

A suitable gas-collection setup could use a gas syringe and stopwatch.

For each concentration, measure the time needed to collect the same volume of gas.

Repeat the measurements and compare the results.

Step 5: Explain How to Improve Reliability

Repeat the experiment for each concentration.

Check for anomalous results and calculate a mean from suitable repeated readings.

This helps reduce the influence of random variation.

You should also consider safety, including wearing eye protection and keeping hydrogen away from ignition sources.

Experiments involving chemicals and gases should only be carried out in an appropriately supervised laboratory.

The main lesson: A strong planning answer shows what you change, what you measure and what you keep constant.

Graphs can feel time-consuming.

But a consistent routine makes them easier.

Imagine you're given results showing how the volume of gas increases during a chemical reaction.

Start by identifying the variables.

Horizontal axis (x-axis): Time in seconds.

Vertical axis (y-axis): Volume of gas in cm³.

Choose a sensible scale that uses the available graph space.

Plot every point carefully.

If appropriate, draw a smooth curve or best-fit line rather than automatically connecting every point with straight segments.

Always follow the exact instruction in the question.

What Does the Shape of the Graph Mean?

At the start of some reactions, gas is produced quickly.

The graph rises steeply.

As the reaction slows, the curve becomes less steep.

When the reaction stops producing gas, the graph levels off.

Understanding this relationship helps you explain the result instead of simply describing a line.

Quick reminder: Include units on both axes, when applicable.

1. Giving a Conclusion Instead of an Observation

If the question asks what you observe, describe what happens.

Don't jump straight to naming a chemical.

For example, "a white precipitate forms" is an observation.

"The substance contains chloride ions" is a conclusion that needs supporting test results.

2. Forgetting Units

A number alone may not be a complete answer.

Always check whether the question involves temperature, volume, time, mass or rate.

3. Confusing Accuracy and Reliability

Accuracy concerns how close a measurement is to the correct value.

Reliability concerns whether repeated measurements give consistent results.

Repeating an experiment can help assess reliability, but it does not automatically remove systematic errors.

4. Suggesting Vague Improvements

"Use better equipment" doesn't explain much.

A stronger answer is more specific.

For example, "use a gas syringe instead of estimating gas volume from bubbles" explains an actual improvement in measurement.

5. Ignoring the Command Word

Cambridge uses different command words for different tasks.

State usually needs a short factual answer.

Describe asks you to say what happens.

Explain asks you to give a reason.

Calculate requires numerical working and a suitable answer.

Before you start writing, underline the command word.

It can stop you from giving the right information in the wrong way.

If you're short on time, don't try to revise everything at once.

Give each study session one clear purpose.

Day 1: Apparatus and Measurements

Review common laboratory equipment.

Practise choosing the correct instrument for measuring volume, temperature, time and mass.

Finish with a few questions on reading scales.

Day 2: Chemical Tests

Revise gas tests, metal ions and anions.

Focus on observations.

Try answering questions without looking at your notes, then use the official qualitative analysis sheet to check.

Day 3: Calculations and Graphs

Practise temperature changes, reaction rates, titration readings and graph interpretation.

Check your units every time.

Day 4: Experimental Planning

Work through questions involving independent, dependent and controlled variables.

Practise describing fair tests and suitable safety precautions.

Day 5: A Full Past Paper

Attempt one complete Paper 6 under timed conditions.

Give yourself 60 minutes.

Then use the mark scheme to review your answers.

Don't just calculate your score.

Look at why you lost each mark.

Was it a missing observation? A calculation mistake? An incomplete explanation?

This tells you what to practise next.

Past papers are valuable, but only if you use them to understand your mistakes.

Start with one paper.

Mark it carefully.

Then create a short mistake log using three headings:

Question or topic: What was the question testing?

My mistake: What went wrong?

Correct approach: What should I do next time?

For example:

Topic: Gas collection experiment.

My mistake: I forgot to keep the temperature constant.

Correct approach: Identify the independent variable, dependent variable and control variables before writing my method.

Review the same skill a few days later.

This is more useful than completing several papers without checking what you learned.

Cambridge also publishes examiner reports and specimen assessment materials. Use these alongside the syllabus to understand how practical skills are assessed.

Remember that older past papers may not fully reflect your examination year's syllabus.

If your child keeps saying, "I understand Chemistry, but I lose marks in practical questions," start by finding out where the difficulty lies.

It may not be the scientific knowledge itself.

Some students struggle to interpret questions.

Others understand an experiment but find it difficult to explain the method using scientific language.

A simple conversation can reveal a lot.

Ask your child to explain an experiment in their own words.

What is being measured?

Why is that instrument used?

What would make the results more reliable?

You don't need to know all the Chemistry answers.

You're helping your child organise their thinking.

If they repeatedly struggle with the same practical skills, a structured revision plan and targeted feedback can help.

Sometimes a student knows the topic but needs someone to show them how to apply it to an exam question.

That's where individual support can be useful.

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For Chemistry, lessons can focus on experimental techniques, reaction calculations, chemical tests, graphs and exam-style questions.

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Is IGCSE Chemistry Paper 6 Difficult?

Paper 6 can be challenging if you're unfamiliar with practical questions.

But regular practice with experimental methods, observations, calculations and data interpretation can make the paper more manageable.

How Many Marks Is Cambridge Chemistry Paper 6 Worth?

Paper 6 is worth 40 marks and contributes 20% of the overall Cambridge IGCSE Chemistry 0620 qualification.

How Long Is IGCSE Chemistry Paper 6?

The examination lasts one hour.

All questions are compulsory.

Do You Have to Perform Experiments in Paper 6?

No. Paper 6 is a written Alternative to Practical assessment.

However, you still need to understand how experiments work and why different methods are used.

Are Qualitative Analysis Notes Provided?

Yes. Cambridge provides notes for qualitative analysis in Paper 6.

You should still practise using the information to identify ions and gases.

Is Paper 6 the Same for Core and Extended Students?

Both Core and Extended candidates may take Paper 6.

Their other examination components differ, but Paper 6 assesses practical skills across the syllabus.

Can You Use a Calculator in Chemistry Paper 6?

Yes. Cambridge permits calculators in Paper 6.

Make sure you show your working when required and include appropriate units.

What Is the Best Way to Revise Chemistry Paper 6?

Combine topic-based practice with complete past papers.

Focus on understanding practical methods, interpreting observations and reviewing mistakes using mark schemes.

IGCSE Chemistry Paper 6 isn't about writing the longest answer.

It's about thinking clearly.

Understand what the experiment is testing.

Know why each piece of equipment is used.

Read the observations carefully.

Show your calculations and explain what the evidence means.

And most importantly, don't panic when a question looks unfamiliar.

Break it into smaller parts. Look for what is being measured, changed or observed.

With consistent practice, practical questions can become much more approachable.

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This guide is based on the Cambridge IGCSE Chemistry 0620 syllabus for examinations in 2026–2028. Always check your examination year, syllabus code and component entry with your school or examination centre.