IGCSE Chemistry: the Practical Test and Alternative to Practical

What the papers test

Cambridge lists the contexts candidates should be familiar with: simple measurements of volume, mass, temperature, time and length; rates of reaction; salt preparation; filtration, crystallisation, simple and fractional distillation and chromatography; electrolysis; identification of metal ions, non-metal ions and gases; chemical tests for water; test-tube reactions of dilute acids; tests for oxidising and reducing agents; heating and cooling curves; titrations; solubility; melting and boiling points; displacement reactions; temperature changes during reactions; rusting and corrosion; and procedures with simple apparatus in unfamiliar situations.

The skills are the same in both papers: selecting and safely using apparatus, planning experiments (independent, dependent and controlled variables, range of values, risks), taking readings to an appropriate precision, recording results in tables with units, plotting graphs with best-fit lines, finding gradients and intercepts, identifying anomalous results, drawing justified conclusions and suggesting improvements. Because Paper 6 candidates cannot handle the apparatus, the paper shows diagrams of thermometers, burettes and gas syringes to read.

Edexcel 4CH1 embeds required practicals in the content, for example paper chromatography (1.13), the formula of a metal oxide (1.36), electrolysis of aqueous solutions (1.60C), the percentage of oxygen in air (2.14), making copper(II) sulfate crystals (2.42), temperature changes (3.8), marble chips and acid (3.15), catalysts for hydrogen peroxide (3.16) and preparing an ester (4.43C). Questions on these appear in the written papers, so Edexcel students revise the same skills without a separate paper.

Tests to know cold

Cambridge Paper 5 and Paper 6 provide the qualitative analysis notes, but theory papers do not, so learn them anyway. Edexcel's sulfate test uses acidified barium chloride solution.

Worked example 1: a titration results table

A student records burette readings for four titrations. Final readings: 25.40, 49.50, 24.80, 49.65 cm^3. Initial readings: 0.00, 24.60, 0.00, 24.80 cm^3. Titres: 25.40 (rough), 24.90, 24.80, 24.85 cm^3.

Readings are recorded to 2 decimal places because a burette is read to the nearest 0.05 cm^3. The rough titre is excluded. The other three are concordant (within 0.10 cm^3 of each other), so mean titre = (24.90 + 24.80 + 24.85) ÷ 3 = 24.85 cm^3. A table should have columns headed with quantities and units, such as "titre / cm^3", not units in every cell.

Worked example 2: identifying an unknown salt

Solution X gives a green precipitate with aqueous sodium hydroxide that does not dissolve in excess. Acidified with dilute nitric acid, it gives a white precipitate with aqueous silver nitrate. Conclusion: X contains iron(II) ions and chloride ions, so X is iron(II) chloride.

Mark-scheme wording: write the observation fully ("green precipitate, insoluble in excess") before the conclusion. Writing "iron(II) present" without the observation, or "green solution" instead of "green precipitate", usually loses the mark. If the precipitate turns orange-brown at the surface on standing, that is iron(II) hydroxide being oxidised, which you can mention as an extra observation.

Common mistakes

• Recording thermometer readings to whole numbers when the scale allows 0.5 °C, or burette readings to 1 decimal place.
• Drawing graphs dot to dot instead of a best-fit line or smooth curve, or using less than half the grid.
• Writing "use more accurate equipment" as an improvement. Name it: a burette instead of a measuring cylinder, a gas syringe instead of collecting over water.
• Saying "repeat to make it accurate". Repeats improve reliability and help spot anomalies; accuracy needs better methods or apparatus.
• Describing a colour as "clear" when you mean colourless.
• In planning answers, forgetting to state what is measured, how, and how often.

Exam technique

Read every instruction twice in Paper 5: the Confidential Instructions shape the apparatus, but the question tells you exactly what to record. Work steadily; 1 hour 15 minutes for 40 marks with experiments is tight. In Paper 6, practise reading scales from diagrams, because several marks come from reading a burette, thermometer or syringe correctly.

For planning questions, structure the answer: apparatus, method in numbered steps, variables kept the same, measurements and their frequency, how to process results (for example rate = volume ÷ time, or plot a graph), and a safety precaution linked to a named hazard. Examiners reward specific quantities, such as 25.0 cm^3 measured with a volumetric pipette.

How one-to-one lessons help

Students who never do the Practical Test in a real lab, or who sit Paper 6, often treat it as an afterthought, yet it carries a fifth of the marks. A tutor works through past Paper 6 questions on the shared whiteboard, trains scale reading, table design and graph plotting, and drills the ion and gas tests with the exact observation wording. For Edexcel students, the tutor turns each required practical into the kind of written question Pearson sets.

Self-check

1. Know whether your school enters you for Paper 5 or Paper 6, and the time and marks for each.
2. Read a burette, thermometer and gas syringe to the right precision.
3. Draw a results table with headings and units.
4. Pick concordant titres and calculate a mean.
5. Give the test and result for each gas and common ion.
6. Plot a graph with a best-fit line and identify an anomalous point.
7. Write a plan with variables, method, measurements and safety.