SEC G3 Combined Science Chemistry component K326/K328
C1: Experimental Chemistry
Choose apparatus, gas collection, separations, chromatography comparisons, and purity evidence for the stated task.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Experimental chemistry is a chain of decisions: choose a measurement that answers the question, choose a separation based on physical properties, and keep observations distinct from conclusions.
Measuring and collecting
Use a stopwatch for time, thermometer for temperature, and balance for mass. A measuring cylinder gives routine liquid volumes, a pipette transfers one accurate fixed volume, and a burette delivers an accurately measured variable volume.
A gas syringe measures gas volume directly. Collection over water is suitable only when the gas has low solubility and does not react with water. A rate setup also needs a definite starting event and readings at known times.
Separating mixtures
Base the method on solubility, particle state, and boiling point. A solvent, filtration, and crystallisation or evaporation can separate suitable solid mixtures. Distillation recovers a solvent, while fractional distillation separates miscible liquids with different boiling points.
Paper chromatography separates soluble substances as a solvent carries them over paper. Select the method only after identifying which component should remain as residue, filtrate, distillate, or crystal.
Chromatograms, identity, and purity
Compare the number and positions of sample spots with known samples. The Combined syllabus requires comparison, not Rf calculation.
A pure substance has characteristic melting and boiling data. Agreement with a reference can support identity, while a shifted value or range can indicate impurity, subject to measurement quality.
Formulae and relationships
This chapter is assessed mainly through models, field patterns and explanations. Build the causal chain before adding any calculation.
Worked examples
Example 1: How would you obtain dry crystals of a soluble salt from a mixture containing that salt, water, and sand?
- Filter to remove insoluble sand.
- Heat the filtrate gently until it is concentrated.
- Cool to crystallise, filter the crystals, and dry them.
Answer: Use filtration, concentration, cooling crystallisation, final filtration, and drying.
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Explain Measuring and collecting with the named terms, evidence, and causal links kept distinct.
- Use Separating mixtures to interpret the evidence given and justify each conclusion.
- Apply Chromatograms, identity, and purity to a new example, then check the conclusion against the information given.
Official outcome coverage
K326 C1: 6 mapped outcomes, references C1.1(a), C1.1(b), C1.2(a), C1.2(b), C1.2(c), C1.2(d). Check the official K326 syllabus.
K328 C1: 6 mapped outcomes, references C1.1(a), C1.1(b), C1.2(a), C1.2(b), C1.2(c), C1.2(d). Check the official K328 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Choose apparatus for time, temperature, mass or volume by range and precision; collect gases appropriately; compare chromatograms with known samples; and select filtration, crystallisation, evaporation or distillation from the mixture. Record observations separately from inferences and keep Rf calculation outside this syllabus.
Exam traps and retrieval check
Avoid these traps
- Choosing apparatus without considering precision.
- Using simple distillation for several miscible liquids with close boiling points.
- Calculating an Rf value when only spot comparison is required.
Check from memory
Which apparatus delivers one accurate fixed volume?
A pipette.
What property makes fractional distillation possible?
Different boiling points.
What can a melting range suggest?
Impurity.
Official Combined Science scope
This shared Combined Chemistry owner serves both K326 and K328. Measurement apparatus, gas collection, rate measurements, mixture separation, chromatogram comparison, and purity evidence without Rf calculation.