The situation
You revise. You understand most lessons. Yet test after test comes back at a C, or just under. More hours of the same revision do not move it.
That pattern is useful. A grade that will not move usually means marks are leaking from the same few places every time. Find those places and the revision can go where it actually pays.
Extended candidates sit Papers 2 and 4, plus Paper 5 or 6, and can achieve A* to G. Cambridge’s entry guidance puts students who have studied the Supplement content and expect a C or above on Extended. If you are on Core and scoring near the top, ask your teacher about Extended now. It means learning the Supplement content as well, so the earlier the better.
Why marks stall at a C
For Extended students, these are the common leaks. Most students have two or three of them, in different amounts.
Diagnose your own case
Do not guess which leak is yours. Sit one full Extended set under timed conditions: Paper 2, Paper 4 and Paper 6. Use Paper 6 even if you sit Paper 5, because it tests the same skills on paper. Mark it with the mark schemes. Then label every lost mark with one symptom from this table.
| Symptom in your marked paper | Likely cause | The fix |
|---|---|---|
| Blank or guessed answers on mole, titration or formula questions | Supplement content not learned | Learn the topic from the notes, then do its past-paper questions |
| Right idea, wrong number, often a factor of 1000 out | Method slip: units or mole ratio | One written routine for every calculation |
| Could not recall a test, definition or colour | Recall gaps | Recall checklists, covered, every week |
| Low marks on the practical paper despite good theory | AO3 skills never practised | One practical-paper question set each week |
| Correct chemistry, half the marks | Command word misread | Underline the command word before writing |
A general guide. Your own split of causes will differ, which is the point of sorting.
Then weigh the losses. Each paper counts for a fixed share of the qualification, but the papers have different numbers of marks. So one raw mark is not worth the same everywhere.
| Paper | Raw marks | Weighting | Share of the total per raw mark |
|---|---|---|---|
| Paper 2 (multiple choice) | 40 | 30% | 0.75 percentage points |
| Paper 4 (theory) | 80 | 50% | 0.625 percentage points |
| Paper 6 (alternative to practical) | 40 | 20% | 0.5 percentage points |
Marks and weightings from Cambridge’s 0620 syllabus for 2026 to 2028, checked 19 October 2026. Paper 5 has the same marks and weighting as Paper 6. Share per mark is weighting divided by raw marks: an illustration of relative weight, not how a grade is calculated.
On weighting alone, ten marks lost on Paper 2 cost 7.5 percentage points of the total. Ten lost on Paper 6 cost 5. A multiple-choice mark carries 1.5 times the weight of a practical-paper mark, so careless multiple-choice errors are expensive.
The fix, step by step
-
Settle your tier
Confirm with your teacher which papers you are entered for. If you are on Core and want above a C, discuss Extended early, because it adds the Supplement content.
-
Sort, then rank the leaks
Using the diagnostic, count lost marks by cause. Multiply by the share per mark in the table above if the totals are close. The biggest bucket is this month’s main job.
Tip. Start with the biggest leak, even if another topic feels more urgent. -
Fix content gaps topic by topic
Read the topic once in the notes, then do the chapter’s recall checklist with the notes covered. Finish with that topic’s past-paper questions, marked strictly.
-
Write every calculation the same way
Equation, values with units, conversion, substitution, answer with unit. Write it out even when the step feels obvious. The worked example below shows why.
Tip. Convert volumes to dm³ before using c = n ÷ V, every time. -
Give the practical paper its own slot
Do one practical-paper question set a week. Practise drawing results tables, plotting graphs, spotting anomalies and suggesting improvements.
-
Re-sit and re-sort after four weeks
Sit a fresh set from a different series and sort the lost marks again. Then re-rank and move to the next leak.
Here is a common method slip, in a question of our own.
A 25.0 cm³ sample of sodium hydroxide solution contains 0.0020 mol of NaOH. Calculate its concentration in mol/dm³.
How to tell it is working
Measure the leaks, not the hours. Track three numbers from your own marked work.
Do not convert practice papers into predicted grades. Grade thresholds are set for each series, so last year’s boundary is only a rough guide. Falling leaks are the honest sign of progress. This method improves the odds; it guarantees no grade.
Where to go next
Do the diagnostic first. Everything else depends on knowing where your marks really go.