OCR 21st Century GCSE Chemistry required practicals: A complete guide

If you're on OCR Twenty First Century Chemistry B (spec code J258), there are 8 compulsory practical activities you need to know about. OCR calls them PAGs rather than required practicals, which is the first thing that trips people up when they start looking around for revision resources.

Each PAG is a group of techniques, not one specific experiment. Your school picks the activity they want to run (or devises their own), and as long as it covers the apparatus and skills in the spec, it counts. That's why two students on the same course can end up having done quite different experiments for the same PAG.

This guide walks through all 8 OCR B Chemistry PAGs in the order the spec lists them, explains how they're examined across the Breadth and Depth papers, and shows the three places OCR B differs from OCR Gateway Chemistry A. A quick language note before we start: OCR says PAGs, AQA says required practicals, Edexcel says core practicals. Same idea, different label. This article is OCR Twenty First Century (OCR B) only.

The OCR specification says you must complete at least eight practical activities, which OCR has grouped into eight Practical Activity Groups based on the Department for Education GCSE subject content requirements. On OCR B separate Chemistry the labels are PAG1 to PAG8. Gateway separate Chemistry (J248) uses the same groupings but labels them PAG C1 to PAG C8, so a C-prefix doesn't automatically mean Combined Science.

At Higher tier, the papers are J258/03 (Breadth) and J258/04 (Depth). Each is 1 hour 45 minutes, each is worth 90 marks, each is 50% of the qualification.

Because each PAG is a group of techniques rather than a prescribed experiment, two schools can teach PAG 8 using totally different reactions. One school might run hydrochloric acid with marble chips. Another might go for sodium thiosulfate with hydrochloric acid. Both tick the box. OCR publishes example activities, but centres can swap them out as long as the techniques get covered.

There's no separate practical exam on OCR B Chemistry. Your school signs a Practical Science Statement confirming you've done the PAGs, and that's the only paperwork side of it. All the actual marks come from written questions on the Breadth and Depth papers. The OCR specification states: "No less than 15% of the questions will assess practical skills."

AO1 (demonstrate knowledge and understanding) and AO2 (apply knowledge and understanding) each account for 40% of the overall grade. AO3 (analyse, interpret, evaluate and improve) picks up the remaining 20%. So you can picture practical questions as where AO3 shows up most of the time, with AO2 right behind it.

Chemistry also has a maths floor of 20% across the papers, set by Ofqual at Level 2. A fifth of the marks need to involve calculation, formula rearrangement or data analysis. Some PAGs lean into that more than others. PAG 6 Titration is the obvious one, where you'll be expected to calculate concentration using moles equals concentration times volume. PAG 8 Measuring rates is the other, where you're interpreting gradients and reading off tangents.

OCR B also runs an entire chapter called C7 Ideas about Science on separate J258. C7 isn't a PAG. It covers scientific method, data interpretation and ethics, often framed around real-world contexts. A lot of the Depth paper's extended-response questions sit at the intersection of a PAG and C7, which catches people out if they've only revised the practicals in isolation.

The practical-skills chapter on OCR B separate Chemistry is Chapter C8.

OCR Twenty First Century Chemistry B differs from OCR Gateway Chemistry A in three places, and if you're revising from a resource aimed at the wrong one, you'll notice pretty quickly.

The first difference is the PAG labelling. OCR B separate Chemistry (J258) labels its 8 PAGs PAG1 to PAG8. OCR Gateway separate Chemistry A (J248) labels the same 8 groups PAG C1 to PAG C8. The PAG titles overlap closely across both specs (reactivity trend, electrolysis, separation techniques, distillation, identification of species, titration, production of salts, measuring rates of reaction), so it's easy to mistake one for the other if you don't check the codes. If a resource only shows five C-prefixed PAGs, that's a Combined Science list, not a separate-Chemistry one.

The second difference is paper structure. Gateway separate Chemistry (J248) splits content between papers, so you can revise "paper 1 topics" and "paper 2 topics" separately. OCR B doesn't work like that. Both the Breadth and Depth papers cover all chapters, and the only thing that differs between them is the question style. Breadth is multi-topic shorter questions; Depth is deeper application and extended-response synoptic reasoning. Going into Breadth expecting a paper on topics X to Y will leave you flipping through questions that could be about anything.

The third difference is the chapter names. OCR B uses narrative-led titles: C1 Air and water, C2 Chemical patterns, C3 Chemicals of the natural environment, C4 Material choices, C5 Chemical analysis, C6 Making useful chemicals, C7 Ideas about Science, C8 Practical skills. Gateway uses more conventional topic labels. Swapping chapter labels between the two courses is one of the most common revision slips, especially when students are using mixed sources.

Reading through the method isn't enough. PAGs are testing whether you can think like a scientist, not whether you can recite a recipe, and that's where a lot of students lose marks they didn't expect to lose.

For each PAG, pick the activity your class actually ran and try writing the method out from memory. Then check it against your notes or a Cognito video. The steps you forgot are the ones that would have cost you marks. Pay attention to the small details OCR likes to probe: using a pipette and a volumetric flask for concentration work in PAG 6, reading a burette at eye level with the meniscus on the line, calculating R_f as substance distance over solvent distance in PAG 3, running flame tests with a clean nichrome wire dipped in concentrated hydrochloric acid between tests in PAG 5. These are the kinds of specifics mark schemes reward with a single word.

The questions that come up for every PAG tend to fall into four shapes: method, variables, explaining results, evaluation and improvement. Prepare an answer for each. On evaluation, you want a specific improvement with a specific reason, not "repeat it".

The quantitative PAGs are worth sketching the expected graphs for. On PAG 8 Measuring rates, that's a curve that rises (gas volume) or falls (mass of reaction flask) over time, with the initial gradient steepest and the plateau representing complete reaction. On PAG 6 Titration, a sharp pH jump near the equivalence point when you plot pH against volume added. On PAG 2 Electrolysis, a labelled diagram of the circuit with correct symbols for the electrodes and electrolyte. If you can draw these from memory before an exam, you'll find yourself way ahead on the first mark of any data question.

For the Depth paper, practise linking a PAG to C7 Ideas about Science reasoning. A question on PAG 1 can swerve into evaluating whether a conclusion is justified given variability in the data, or whether a model (electron configuration, for example) explains an observed pattern. Our guide to getting a grade 9 in GCSE Chemistry walks through these synoptic patterns and other exam techniques worth practising.

The best thing to do, once you've got the content down, is to work through past paper questions sorted by PAG. OCR recycles wording and graph shapes year on year, and the mark schemes are the clearest guide to the exact phrases they want.

Our OCR Twenty First Century Chemistry course covers all 8 PAGs through short video lessons, worked examples and exam-style questions. Each PAG has its own lesson walking through the technique, apparatus, variables and exam language. Jump into the OCR B Chemistry course and track your progress through the whole spec. For the wider shape of the qualification, our complete guide to OCR Twenty First Century GCSE Chemistry covers Breadth and Depth paper structure, chapter list and timing in one place.