Cambridge IGCSE Chemistry Paper 5 and Paper 6: practical skills

Comparing Paper 5 and Paper 6

Feature	Paper 5 · Practical Test	Paper 6 · Alternative to Practical
Duration	1 hour 15 minutes	1 hour
Marks	40	40
Qualification weighting	20%	20%
Assessment objective	AO3 · 100%	AO3 · 100%
Examination setting	carrying out experiments in a laboratory	written analysis and planning of experiments
Qualitative-analysis notes	provided	provided
Entry	school / examination centre	school / examination centre

A candidate takes only one of these papers. The school or examination centre manages the choice; ask which paper is included in the candidate's entry at the start of preparation. Either Paper 5 or 6 may be used for both Core and Extended candidates, and both assess across the full grade range.

Paper 5 is longer because the candidate physically carries out investigations while recording data and observations. Paper 6 contains no experiment performed during the examination, but its diagrams, data and planning questions require rapid, accurate interpretation of laboratory situations. The balance of practice may therefore differ, but neither paper can be reduced to simple factual recall.

Keep a separate list of logistical routines for the correct paper. Paper 5 candidates should practise following instructions in sequence, recording raw data immediately and dividing time among the experiment, graph and written answers. Paper 6 candidates should practise reading apparatus diagrams, identifying missing steps and writing plans that are concise yet reproducible.

In both papers, laboratory vocabulary is most useful when linked to an operation. Do not merely recognise a burette: know when to read it, how to calculate the volume delivered and what error an air bubble causes. Similarly, learn filtration, evaporation and crystallisation with their purposes and correct sequence.

The same AO3 in different settings

AO3 requires candidates to select safe techniques, apparatus and materials; plan investigations; record observations and measurements; interpret data; and evaluate and improve methods. In Paper 5, some of these decisions become visible through practical work. In Paper 6, the same decisions are made from diagrams, descriptions and data.

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.

Online study can develop planning, graph work and evaluation strongly, but it does not replace genuine laboratory experience. Reading a pipette, handling a burette, assembling filtration apparatus or observing gas evolution are physical routines. The school or examination centre should provide these in a safe laboratory environment.

Choosing apparatus: begin with the required precision

The best apparatus is not the item seen most often, but the one whose range and resolution suit the measurement.

Task	Suitable choice	Why?	Weak choice
measure exactly 25.0 cm3 of solution	25.0 cm3 volumetric pipette	fixed volume, high precision	graduations on a beaker
deliver a variable volume precisely	burette	fine reading and controlled delivery	measuring cylinder when titration precision is needed
measure gas volume over time	gas syringe	direct volume reading	inverted test tube when quantitative data are needed
measure a change in mass	balance with suitable resolution	numerical, repeatable data	a quantity estimated “by eye”

Always state what is measured, with which apparatus, in which unit and, where relevant, at what resolution. “Use more accurate apparatus” is a weak improvement by itself; name, for example, the burette replacing a measuring cylinder and the uncertainty it reduces.

Apparatus choice: three questions before naming an item

First decide whether a fixed or variable quantity is required. Second, estimate the expected range: a gas syringe with a 100 cm³ maximum is unsuitable if the expected gas volume exceeds it. Third, check whether the reading uncertainty is small enough relative to the measured change. A 2 cm³ difference measured with a cylinder marked every 1 cm³ may have a large relative uncertainty.

For a diagram question, check the entire setup. A gas apparatus should be sealed, connections stable, the measuring device oriented correctly and the reaction started without unmeasurable early loss. If asked for a fault in the diagram, state its specific consequence rather than only circling the component.

Observation, evidence and inference

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.

An observation records what the senses or instrument show: “a light-blue precipitate formed”, “the temperature rose from 21.0 °C to 27.5 °C”, or “the gas relit a glowing splint”. An inference supplies chemical meaning: the test conditions support identifying an ion or gas, or the measured change indicates an exothermic process.

Avoid circular statements such as “oxygen was formed because oxygen was formed”. State the test and its result. In qualitative analysis, the reagent and conditions are part of the evidence; the same colour in another setting may support a different inference.

Recording precise data: immediately, with units and consistently

Record raw data immediately during measurement. Values measured with the same apparatus should use consistent decimal places, and the unit belongs in the heading. Put raw and calculated data in separate columns.

For example, if a thermometer graduated in 1 °C divisions is read to whole degrees according to its scale, do not write 24.000 °C arbitrarily. For burette readings, use the decimal places appropriate to the instrument’s expected reading precision. Unjustified digits do not make a measurement more precise.

A weak and an improved results table

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.

A good table can be interpreted by itself. Put the independent variable in the first column and the dependent variable next. Use a heading such as time / s, not a separate “s” after every value. Give repeats separate columns and calculate an appropriate mean; never delete an anomaly without explanation.

If the table must be designed during the examination, leave enough rows and set headings for the expected range. For qualitative results, reagent and observation may occupy separate columns so that an inference does not overwrite the raw evidence. For quantitative repeats, do not average a set containing an obvious anomaly until the differing measurement has been investigated or repeated.

Checklist:

• quantity and unit in every heading;
• consistent precision for the same measurement;
• calculated data never overwrite raw data;
• enough space for the expected range;
• precise qualitative description, not merely “changed”.

Graphs: six checks before and after plotting

Poor graph

Improved graph

1. The independent variable is on the x-axis and the dependent variable on the y-axis.
2. Both axes show a quantity and unit.
3. The scale is simple, even and uses the available area well.
4. Points are plotted with thin, precise marks.
5. A line or curve of best fit represents the trend; it does not necessarily join points in sequence.
6. A gradient uses well-separated points on the fitted line and shows the calculation.

Recognising an anomaly does not automatically justify omitting it. State why it differs from the trend and, if the method allows, repeat that measurement.

Gradient, intercept and extrapolation

For a gradient, take the triangle points from the fitted line, not necessarily from two original data points. Use a large triangle, write the axis units and calculate Δy / Δx. The gradient unit is the quotient of the two axis units.

Interpolation estimates within the measured range; extrapolation estimates beyond it. Extrapolation is less certain because it assumes that the trend continues in the unmeasured range. If the chemical system could approach saturation, equilibrium or a different mechanism, name that limitation.

Planning example: how does acid concentration affect the rate of reaction with magnesium?

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

Question: how does the initial rate of hydrogen production change when hydrochloric acid concentration changes while the amount of magnesium remains constant?

Independent variable: hydrochloric acid concentration, for example five safely selected values. Dependent variable: volume of H₂ produced in a specified time, or time required to reach a specified volume. Control variables: acid volume, magnesium mass and surface area, temperature, apparatus and method of mixing.

Method outline: measure equal volumes of acid solution; use equal lengths of cleaned magnesium ribbon; seal the flask to a gas syringe; start timing when the reaction begins; record the volume at regular intervals; repeat each concentration; calculate a mean if repeats agree; plot initial rate against concentration.

Safety: eye protection, risk control appropriate to the acid concentration, securely clamped apparatus and no naked flame near hydrogen. In the examination, connect the risk to the specific precaution.

Why is this stronger than “keep everything else the same”? It names what remains constant and how. The investigation is reproducible and the data processing answers the original question.

What makes the plan complete rather than a list?

Justify the variable range: at least five sensibly spaced concentrations show a trend more effectively than two extreme values. State the number of repeats and how the mean will be handled. Instead of “measure the rate”, define it: initial gradient from the gas-volume–time graph, reciprocal of the time needed for a fixed volume, or volume produced in a fixed time. Use the same definition at every concentration.

End by stating which graph or comparison answers the question. A detailed method can still be irrelevant if its processed data do not make the levels of the independent variable comparable.

Evaluating a method: error → effect → 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.

Specific limitation	Expected effect	Targeted improvement
gas escapes while the stopper is inserted	measured gas volume is too small, especially initially	start the reaction in a closed system with separated reagent
heat transfers to the surroundings	measured temperature change is smaller than the actual change	insulated vessel and lid; equal starting temperatures
a colour endpoint is noticed too late	delivered volume may be consistently too large	suitable indicator and dropwise addition near the endpoint
apparatus resolution is too coarse	relative uncertainty is large	apparatus with finer divisions and a suitable range

“Human error” is not an evaluation. It does not identify the mechanism that distorted the data, the direction of the effect or the method change that would help. Repeats help identify random variation, but they do not correct every systematic error.

Also distinguish a limitation from a mistake. A limitation is a restriction of the method or apparatus that may remain even with careful work, such as heat transfer to the surroundings. A mistake is a one-off execution error, such as a misreading or spilled solution. A stronger examination evaluation improves the method’s general reliability rather than merely asking the experimenter to “be more careful next time”.

State the direction of an effect only when it follows from the mechanism. Gas lost before collection biases measured volume downwards; noticing a titration endpoint late may produce an excessive burette volume. Variation in reaction time does not necessarily act in the same direction every time.

Qualitative analysis: a short introduction

The official Notes for use in qualitative analysis from the 2026–2028 syllabus are provided in both Paper 5 and Paper 6. The aim is not to memorise the entire table blindly but to use the sample → reagent and condition → observation → inference chain quickly and accurately.

For aqueous chloride ions, for example, the official procedure acidifies with dilute nitric acid before aqueous silver nitrate produces a white precipitate. “White precipitate” without the acidification and reagent is incomplete evidence. For more practice, use the qualitative analysis and ion tests guide.

Three practice plans for the time available

30 minutes per week

One skill and one repair: 10 minutes on a table or graph, 10 minutes checking, 10 minutes rewriting. Apply the same skill to a new dataset the following week.

60–90 minutes per week

Rotate measurement/data, planning/evaluation and qualitative blocks. At the end of each session, record one first wrong step in the error log.

The final eight weeks before the examination

Include Paper 5/6 work every week and gradually lengthen the timed portion. The 8-week IGCSE Chemistry plan shows the complete rhythm.

Common myths

“Paper 6 does not require seeing real experiments.”

False. The paper is written, but it assesses the same experimental situations and AO3 skills. Without safe laboratory experience, apparatus and observations can remain only pictures.

“Points on a graph must always be joined.”

False. Many investigations require a line or curve of best fit representing the trend.

“More repeats solve every error.”

False. Repeats characterise random variation; systematic bias from miscalibrated apparatus or heat loss can remain.

“Paper 5 is harder because it is in a laboratory.”

They cannot be ranked in that way. The setting differs, but both assess the same AO3 with the same marks and weighting.