Chemical Analysis

AQA GCSE Combined Science: Trilogy (8464)

8 ready-made resources for teaching Chemical Analysis, written for AQA GCSE Combined Science. Slides, worksheets, mark schemes, homework, an assessment and retrieval quizzes, all with SEN-friendly scaffolding built in as standard. Below is what the topic requires and where students usually go wrong, free to read whether or not you sign up.

Independently rechecked. These files were written to the specification from our own topic maps, then put through a separate recheck pass from the one that wrote them, which found and fixed real errors. A subject teacher has not signed them off individually, so give them your usual read before you teach from them.

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What is in this bundle

Assessment mark schemeWord, editable
End-of-topic assessmentWord, editable
HomeworkWord, editable
Retrieval-practice quizzesWord, editable
SlidesPowerPoint, editable
Starter & exit ticketWord, editable
Tiered worksheetWord, editable
Worksheet mark schemeWord, editable

Foundation and Higher tier

Define a pure substance, in the chemistry sense, as a single element or compound with nothing else mixed in, distinct from the everyday sense of "pure" (unadulterated, natural), and use melting-point and boiling-point data to distinguish a pure substance (melts/boils at one specific temperature) from a mixture (melts/boils over a range).
Define a formulation as a mixture deliberately designed as a useful product, made by combining components in carefully measured quantities to achieve required properties, and identify examples given appropriate information: including fuels, cleaning agents, paints, medicines, alloys, fertilisers, and foods. Names of components in specific branded products are not required.
Explain how paper chromatography separates a mixture, using a stationary phase and a mobile phase, with separation depending on how each substance distributes between the two phases; calculate an Rf value using Rf = distance moved by substance ÷ distance moved by solvent, interpret chromatograms, and explain how chromatography can distinguish pure substances (a single spot in every solvent) from mixtures (which may separate into multiple spots, and whose spot pattern can vary by solvent): giving Rf answers to an appropriate number of significant figures.
Describe the test for hydrogen: a lit splint held at the mouth of a test tube of the gas produces a rapid "pop."
Describe the test for oxygen: a glowing splint inserted into a test tube of the gas relights.
Describe the test for carbon dioxide: shaking or bubbling the gas through limewater (aqueous calcium hydroxide) turns it cloudy/milky.
Describe the test for chlorine: damp litmus paper placed in the gas is bleached white.

Higher tier only

None: this topic has no content flagged as Higher-tier-only in the specification; both tiers cover identical requirements here.

Required practicals

Required practical 12: use paper chromatography to separate and distinguish coloured substances, calculating Rf values for the separated spots.

Where students go wrong

Using "pure" in its everyday sense (nothing added, natural) rather than its precise chemistry meaning (a single element or compound, nothing else mixed in): these can conflict, since a "pure" fruit juice, for instance, is still a mixture chemically.
Measuring the wrong distances when calculating Rf, particularly measuring from the wrong starting point (the origin line) or to the wrong end point (the centre of the spot, not its edge).
Assuming a substance producing multiple spots on a chromatogram must be impure in every solvent, rather than understanding a single solvent choice might happen not to separate a genuine mixture into visibly distinct spots.
Mixing up the four gas tests, particularly confusing the "pop" (hydrogen) with the "relights" (oxygen) result, since both involve a splint but produce opposite/different outcomes.
Describing the carbon dioxide test result as "clear" rather than "cloudy/milky": the correct positive result is the opposite of what "clear" would suggest.

How it gets asked in the exam

"Describe how you would test for [gas] and state the result", "Explain how chromatography can be used to identify a pure substance", "Calculate the Rf value of substance X", "Explain why melting point data suggests this sample is/isn't pure".

Key vocabulary

Pure substance, formulation, chromatography, stationary phase, mobile phase, Rf value, limewater, litmus paper.

Assumed prior knowledge

Basic understanding of mixtures versus pure substances from Atomic Structure and the Periodic Table (this taxonomy's topic 08).
Comfort with simple ratio/division calculations, needed for Rf values.
Basic significant-figures awareness, needed to give Rf answers to an appropriate precision.

How Speca scaffolds this topic

A single, consistently formatted four-gas-test reference card (gas name, test method, positive result) used repeatedly across worksheets and retrieval quizzes, since these four facts are short, fixed, and benefit from spaced, low-stakes repetition rather than one-off exposure.
A worked chromatogram diagram with the origin line, solvent front, and spot centre explicitly and consistently labelled and colour-coded, used for every Rf calculation example, so measurement errors are caught by habit rather than left to chance.
Formulations benefit from a simple "what's it for, and what does each part do?" question applied to a few concrete, familiar examples (e.g. paint: pigment for colour, solvent for spreadability, binder for adhesion) rather than an abstract definition alone.
Pure-vs-mixture melting/boiling point reasoning benefits from a simple graph comparison (a pure substance's sharp, flat melting plateau versus a mixture's gradual, sloped melting range) shown side by side, making the distinction visually obvious rather than purely definitional.

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