Cambridge IGCSE Chemistry practical and exam skills: how to prepare for Papers 1–6

• Syllabus: 0620
• Examinations: 2026–2028
• Routes: Core + Extended
• Focus: Papers + practical skills

CoreExtended

Selected route: Core

1. Paper 1Multiple choice
2. Paper 3Theory
3. Paper 5 or Paper 6Practical skills

Prepare for the papers the student will actually take

Route	Multiple choice	Theory	Practical skills
Core	Paper 1	Paper 3	Paper 5 or Paper 6
Extended	Paper 2	Paper 4	Paper 5 or Paper 6

Confirm the examination year and route before selecting complete papers. Confirm Paper 5 or Paper 6 with the school; candidates take one, not both. Older questions can be used selectively when the content and skill remain relevant, but an old paper structure should not be treated as the current examination model. A full simulation should use the student’s current paper combination.

The programme overview gives all component times and weights. In brief, Papers 1 and 2 are 45 minutes, 40 marks and 30%; Papers 3 and 4 are 1 hour 15 minutes, 80 marks and 50%; Paper 5 is 1 hour 15 minutes, 40 marks and 20%; Paper 6 is 1 hour, 40 marks and 20%.

Use official papers through authorised sources and under Cambridge’s terms. Every question, worked example and dataset in this guide is original; no restricted paper, mark scheme or candidate response is reproduced.

Knowledge, examination decisions and practical evidence must develop together

Chemical knowledge and application includes retrieving facts and models, selecting the relevant idea, applying it to unfamiliar substances or wording, and connecting topics.

Quantitative and written communication includes choosing a calculation route, showing chemically meaningful working, using units and suitable precision, answering the command word, and building a complete causal explanation.

Experimental evidence includes observing and measuring, recording data consistently, processing results, planning variables and controls, and evaluating limitations and improvements.

Chemical knowledge and application

Retrieve, select and apply chemical models in unfamiliar contexts.

Quantitative and written communication

Choose a calculation route and expose relationships, units and complete reasoning.

Experimental evidence

Observe, measure, process, plan and evaluate evidence.

The families overlap. A theory paper can contain experimental data; a practical paper can require calculations and chemical explanation. Preparation fails when it treats “practical” as a separate final chapter or assumes that knowing the Chemistry automatically produces a complete written answer.

Multiple choice rewards discrimination, not only recall

For Papers 1 and 2:

1. Read the stem and identify what must be decided.
2. Predict the relationship or result when possible.
3. Eliminate chemically impossible choices.
4. Estimate before committing to a long calculation.
5. Check unit, sign, direction and order of magnitude.
6. Flag a difficult item and return rather than spending disproportionate time.
7. During correction, record why the chosen distractor looked plausible.

Consider this original illustrative item. Magnesium reacts according to Mg + 2HCl → MgCl₂ + H₂. A mixture contains 0.10 mol Mg and 0.15 mol HCl. What amount of hydrogen can form?

• A · 0.050 mol: might come from inventing a 2:1 Mg:H₂ ratio.
• B · 0.075 mol: correct; HCl is limiting and the HCl:H₂ ratio is 2:1.
• C · 0.100 mol: ignores that only 0.15 mol HCl is available.
• D · 0.150 mol: copies the limiting-reactant amount without applying the mole ratio.

The useful information is not only that B is correct. Each wrong option identifies a different repair: interpreting coefficients, finding the limiting reactant or applying the ratio. A question bank becomes diagnostic when distractors are analysed this way.

A correct idea must become a complete, visible answer

For definitions and short statements, use the required scientific term and avoid extra claims that create contradictions. Distinguish state, describe and explain: the first may require a concise fact, while the last needs a causal connection.

For calculations, write the relationship, substitutions and ratios; keep suitable precision and give the final unit. Visible working allows both the marker and the student to locate the first incorrect step.

For explanations, use cause → process → consequence. Compare:

Incomplete: The reaction is faster because the particles move faster.

changed condition: At the higher temperature, particles have particle energy: greater kinetic energy. A larger proportion have energy activation-energy threshold: equal to or greater than the activation energy, so successful-collision consequence: the frequency of successful collisions increases.

1. 1changed condition
2. 2particle energy
3. 3activation-energy threshold
4. 4successful-collision consequence

The stronger version identifies the changed condition, particle-level effect, activation-energy link and observed consequence. Memorising a long sentence is not the objective; the learner should recognise which causal links the new question requires.

For data-based responses, describe the evidence before explaining it. Quote relevant values where useful, separate an overall trend from an anomaly and do not force the data to support the expected theory. “As temperature rises, the time falls” is a description; collision theory is the later explanation.

Both practical papers assess understanding in different conditions

Feature	Paper 5: Practical Test	Paper 6: Alternative to Practical
Performed in a laboratory during the paper	Yes	No
Time	1 hour 15 minutes	1 hour
Marks	40	40
Weight	20%	20%
Direct measurement and observation	Central	Interpreted through written material
Planning, data and evaluation	Assessed	Assessed

Paper 6 should not be taught as a list of memorised experiments. Paper 5 preparation must include procedural fluency, not merely theoretical familiarity. Both require understanding why an apparatus, range, control, repeat or improvement is appropriate.

Official contexts include quantitative measurements, rates, salt preparation, separation and purification, electrolysis, qualitative analysis, acids, oxidising and reducing agents, heating and cooling curves, titrations, solubility and melting or boiling points. This list describes possible syllabus contexts; it is not a prediction of a particular paper.

Record the evidence before naming the explanation

Observation

The damp red litmus paper turned blue.

→

Inference

The gas was alkaline; under the stated test conditions this supports the identification of ammonia.

---

Observation

The temperature increased from 21.0°C to 27.5°C.

→

Inference

The measured temperature change is consistent with an exothermic process in the experimental system.

The litmus colour change is observed; identifying ammonia is an inference supported under the stated test conditions. Likewise, a thermometer reading is evidence. Calling the process exothermic interprets that evidence in the experimental system.

An inference should not claim more than the test establishes. A gas test may support an identification without proving the complete identity of an unknown sample. A temperature rise supports an exothermic interpretation but does not automatically quantify all energy transferred or exclude every source of heat exchange.

A reader should be able to reconstruct what was measured

A useful table title identifies the experiment or relationship. Put the independent variable first and units in headings, not inconsistently inside cells. Recorded precision should reflect the instrument and method. Keep repeats visible, distinguish raw from processed values and retain anomalies transparently unless a justified rule supports exclusion.

Poor table — demonstration of common presentation problems

Temp	Time	Time	Mean
20°C	82.4 sec	83 sec	82.7
40	44.8s	44.5	44.7
60°C	23.6 sec	23.4s	23.5

Repeats are unclear, units sit in cells, precision varies and an anomalous value has disappeared.

Improved table

Temperature / °C	Repeat 1 / s	Repeat 2 / s	Repeat 3 / s	Mean / s
20.0	82.4	83.0	82.6	82.7
30.0	61.3	60.8	61.1	61.1
40.0	44.8	44.5	65.2‡	44.7‡
50.0	32.7	32.4	32.6	32.6
60.0	23.6	23.4	23.5	23.5

‡ The 65.2 s value is retained and flagged; the 44.7 s mean of the two consistent repeats is used only after the exclusion rule is explained.

The improved table does not pretend the 65.2 s value never existed. It marks the value, keeps the raw evidence and states how the displayed mean was treated. If exclusion cannot be justified from the method and repeats, the student should not remove a point merely because it makes the graph look untidy.

A graph is an argument about a relationship, not decoration

Place the independent variable on the horizontal axis where appropriate and the dependent variable on the vertical axis. Label each with quantity and unit, use the plotting area effectively, plot accurately and choose a line or curve suited to the relationship. Identify an anomaly rather than hiding it. Show gradient or interpolation work transparently when required.

Poor graph

Improved graph

For a data response:

1. identify variables and units;
2. describe the overall pattern;
3. support it with values;
4. identify an anomaly or limitation; and
5. explain only with Chemistry justified by the data and question.

Do not assume every dataset needs a straight line. Equally, do not join every point merely because software can. The representation should help answer the stated question.

Find the first invalid step, not only the wrong final number

Use a seven-step route:

1. State the required quantity.
2. Select or write the relevant relationship.
3. Convert units.
4. Calculate the starting chemical quantity.
5. Apply the balanced-equation ratio when relevant.
6. Give the final value with unit and suitable precision.
7. Check physical and chemical plausibility.

Calculation audit trail

1. relationship

   Required quantity: concentration of product solution in mol dm⁻³.

2. conversion

   Convert 250 cm³ to 0.250 dm³ before using concentration = amount ÷ volume.

3. ratio

   2.40 g of Mg gives 2.40 ÷ 24.0 = 0.100 mol Mg; the illustrative equation gives a 1:2 ratio, so 0.200 mol product forms.

4. result

   Concentration = 0.200 ÷ 0.250 = 0.800 mol dm⁻³.

5. check

   The unit is correct and the value is plausible for 0.200 mol distributed through one quarter of a dm³.

Show the first common failure

The original worked example deliberately includes molar mass, amount of substance, a 1:2 mole ratio and conversion from cm³ to dm³. Because each decision is visible, correction can target the first invalid relationship instead of asking the student to copy a final number.

A method should produce evidence that can answer the question

A repeatable planning canvas asks for:

1. a focused question;
2. an independent variable and useful range;
3. a measurable dependent variable;
4. important controls and the action used to control each;
5. apparatus and why it is suitable;
6. an ordered procedure with quantities;
7. repeats;
8. a planned table and graph;
9. safety linked to named hazards; and
10. a decision rule for the conclusion.

For example, a student might investigate how acid concentration affects the time required to produce a fixed volume of gas from a carbonate. Concentration is varied across a justified range; the measured outcome is the time to a fixed volume. Temperature, acid volume, carbonate mass and particle size need named control actions. “Keep everything else the same” does not say how any variable will be controlled.

The example demonstrates measurement logic, not a complete investigation ready for submission. The student still has to decide suitable values, apparatus, safety, repeats and a conclusion rule for their own context.

Question________________________________________________Independent variable and range________________________________________________Dependent variable and measurement________________________________________________Controls and actions________________________________________________Suitable apparatus________________________________________________Repeats________________________________________________Table/graph plan________________________________________________Safety________________________________________________Conclusion rule________________________________________________

Evaluate the method, not the student’s character

Use the causal chain specific limitation → effect on measurement → effect on result → feasible improvement.

1. Specific limitationDelay between mixing and sealing the flask.
2. Effect on measurementGas made during the delay escapes.
3. Effect on resultRecorded gas volume is systematically too low.
4. Feasible improvementSeal first; add one reactant through a dropping device after recording begins.

“Human error occurred” does not identify an action, direction of effect or repair. “Use more accurate equipment” also fails unless the relevant limitation, improved resolution and expected consequence are stated.

Repeats help reveal variation and make a mean possible. They do not automatically remove systematic bias: repeating a method that always loses gas before sealing can produce several consistent values that are all too low. The improvement must change the cause of that bias.

Every lost mark should create a specific next task

Use codes such as K knowledge or chemical model, Q quantitative setup, C command word or communication, D data interpretation, P practical method and T time management or rushed reading.

Record the date, paper and question type, topic, first incorrect decision, repair task, retry date and transfer result in a new context. “Do more practice” is not schedulable. “Complete four solution questions that begin by calculating amount, then explain the first step aloud” is.

One sample error-log entry

Date	Paper/type	Code	First incorrect decision	Repair task	Retry evidence
14 March	Theory calculation	Q	Used concentration directly as amount	Complete four solution questions beginning with moles; explain the first step aloud	3/4 correct independently on 18 March

The balance changes as the examination approaches

With more than twelve weeks, begin with a mixed diagnostic, repair major dependencies, include regular practical work, use short paper-specific sets and reserve full simulations for later. With six to eight weeks, compress the diagnostic and combine targeted repair with timed sections every week. With two to four weeks, do not restart the entire syllabus: stabilise reliable methods, practise the correct papers, focus on recurring errors and protect sleep and concentration.

12+ weeks

DiagnoseMixed diagnostic

RepairRepair major dependencies

Paper practiceShort sets first; full simulations later

Practical skillsRegular practical work

6–8 weeks

DiagnoseCompressed diagnostic

RepairPrioritise recurring high-impact errors

Paper practiceCombine targeted repair and timed sections

Practical skillsMaintain planning, data and evaluation

2–4 weeks

DiagnoseDo not restart the entire syllabus

RepairStabilise reliable methods

Paper practicePractise the correct paper combination

Practical skillsConsolidate routines and protect sleep

A 90-minute session might use 15 minutes for retrieval from earlier topics, 30 minutes for one targeted weakness, 30 minutes for paper-specific questions and 15 minutes to mark, classify and schedule a retry. Difficult correction may need additional time after the nominal session.

Timed work should test a method that is being developed; it should not be the only method. A student who repeats complete papers without changing the first wrong decision simply rehearses the same pattern under pressure.

Parents can monitor the learning process without marking Chemistry

Useful signs include precisely named weaknesses, correction visible in the schedule, a repeated error becoming less frequent, practical skills appearing throughout the plan, timed results becoming more stable and the student being able to explain the next action.

Warning signs include many papers but no error log, repeated errors without a different repair, revision dominated by rereading or watching, no distinction between Core and Extended material, and practical preparation delayed until immediately before the examination.

A useful parent question is:

“What did this paper show you to change before the next attempt?”

This asks about the process without requiring the parent to teach or mark the Chemistry.

Ask for help when a pattern persists despite genuine correction

Support may be useful when every stoichiometry question still feels unrelated, explanations repeatedly stop one step early, Paper 5 or Paper 6 planning remains generic, graphs and tables lose the same marks, performance falls sharply under time pressure, or the student cannot explain why the original answer failed.

A productive consultation begins with the route, examination year and one recent unaided theory paper or practical-skills task. The aim is to separate content gaps from calculation, evidence and examination-performance problems.

Frequently asked questions

How is Paper 5 different from Paper 6?

Paper 5 is a laboratory Practical Test lasting 1 hour 15 minutes. Paper 6 is a one-hour written Alternative to Practical. Both are 40 marks, worth 20% and assess experimental skills and investigations.

Does a Paper 6 student need to carry out practical work during the course?

Yes. Paper 6 requires practical understanding even though no experiment is performed during that paper. Safe hands-on experience supports reasoning about apparatus, observations, measurement and limitations.

How many full papers should a student complete each week?

There is no universal number. The right balance depends on time remaining and what correction reveals. Complete papers are valuable only when substantial attempts are reviewed and repaired.

Can questions from the previous syllabus be useful?

Yes, selectively, after checking that the content and skill remain relevant. Do not use an older complete paper as the model for the current assessment structure.

When should timed practice begin?

Short timed sections can begin while methods develop. Complete simulations become more useful after core decisions are sufficiently stable and should use the correct current paper combination.

How should a mark scheme be used without copying it?

Mark strictly, find the first missing decision, close the scheme, repair the method and rewrite or resolve independently. Later, test the same idea in a different context.

What should be recorded in an error log?

Record the first incorrect decision, its code, a specific repair, a retry date and evidence from a new context—not merely the correct letter or final answer.

Can practical skills be supported in online tutoring?

Data analysis, planning, evaluation, visualised procedures and correction can be taught online. A video call cannot replace supervised hands-on laboratory experience or the school’s safety arrangements.