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Understanding how AQA mark schemes work is just as important as knowing the chemistry. This lesson exposes the patterns that examiners use when marking, the traps that catch students every year, and the precise techniques that consistently earn full marks. If you learn these patterns, you will maximise your marks on every question — even when your knowledge is imperfect.
AQA uses two types of mark scheme:
For questions worth 1–5 marks, the mark scheme lists specific marking points. Each marking point is worth 1 mark, and you must make that exact point (or an acceptable equivalent) to earn the mark.
Example (3 marks): Question: "Explain why the rate of reaction increases when the concentration of acid is increased."
Mark scheme:
Key insight: You must make three distinct points for 3 marks. Writing "the particles collide more" only earns 1 mark (for more frequent collisions). You must also explain WHY (more particles per unit volume) and connect it to SUCCESSFUL collisions.
For 6-mark extended response questions, the examiner reads your whole answer and decides which level it fits into:
| Level | Marks | What the Examiner Looks For |
|---|---|---|
| Level 3 | 5–6 | Detailed, coherent account. All or most of the relevant points made. Logical structure. Correct scientific terminology throughout. Ideas are well-developed and linked. |
| Level 2 | 3–4 | Some relevant points, but the answer is incomplete or partially organised. Some correct terminology. Ideas are present but not fully developed. |
| Level 1 | 1–2 | Simple statements. Limited relevant content. Little or no scientific terminology. Ideas are disconnected. |
| 0 | 0 | No relevant content at all. |
The mark scheme provides indicative content — a list of points that a good answer might include. The examiner does NOT tick off individual points. Instead, they judge the overall quality of the response.
Exam Tip: For 6-mark questions, you do NOT need to make every single point in the indicative content list. But you DO need to make enough points, organise them logically, and use correct scientific language to reach Level 3.
This is the single most common source of lost marks on AQA Chemistry papers. Students lose marks every year because they describe when asked to explain, or vice versa.
When a question says "describe," you should state what you observe or what occurs, step by step. You do NOT need to give reasons.
Example: "Describe what you see when sodium is added to water."
When a question says "explain," you must give reasons. Use words like "because," "this is due to," "as a result," "therefore."
Example: "Explain why sodium is more reactive than lithium."
Balancing chemical equations is worth 2–3 marks on AQA papers. The marks are split:
| Mark | Awarded For |
|---|---|
| Mark 1 | Correct formulae of all reactants and products |
| Mark 2 | Correctly balanced equation |
| Mark 3 (if applicable) | State symbols — (s), (l), (g), (aq) |
Example: Balance the equation for the reaction between magnesium and hydrochloric acid.
Wrong: Mg + HCl₂ → MgCl₂ + H₂ (WRONG formula for HCl — gets 0 marks even though it "looks" balanced)
Correct: Mg + 2HCl → MgCl₂ + H₂ (correct formulae AND balanced = 2 marks)
With state symbols: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g) (3 marks)
| Error | Correct Version |
|---|---|
| Writing HCl₂ instead of 2HCl | You change the big number in front, never the subscript |
| Writing NaOH₂ instead of Na(OH)₂ | Wait — Na only forms Na⁺, so it's NaOH. Ca(OH)₂ is correct for calcium hydroxide. |
| Writing CaO₂ instead of CaO | Calcium is 2+ and oxygen is 2−, so the formula is CaO (1:1 ratio) |
| Writing CO when you mean CO₂ | CO is carbon monoxide (a different, toxic compound) |
| Using lowercase incorrectly: co instead of Co (cobalt) or CO (carbon monoxide) | Case matters in chemistry |
Exam Tip: When balancing equations, write out all the correct formulae FIRST, then adjust ONLY the big numbers in front. NEVER change subscripts to balance an equation — changing a subscript changes the substance.
Calculation questions on AQA papers are marked in stages. Even if your final answer is wrong, you can earn marks for correct working. This is called error carried forward (ECF) — if you use a wrong value from a previous step correctly in a later step, you can still get the method mark.
Formula: Mr = sum of the relative atomic masses of all atoms in the formula
Example: Calculate the Mr of calcium carbonate, CaCO₃. (Ar: Ca = 40, C = 12, O = 16)
Formula: moles = mass ÷ Mr
Example: Calculate the number of moles in 11.0 g of carbon dioxide, CO₂. (Mr of CO₂ = 44)
Formula: concentration (mol/dm³) = moles ÷ volume (dm³)
Remember: To convert cm³ to dm³, divide by 1000.
Example: 0.05 moles of NaOH is dissolved in 250 cm³ of water. Calculate the concentration.
Formula: % yield = (actual yield ÷ theoretical yield) × 100
Formula: atom economy = (Mr of desired product ÷ sum of Mr of ALL products) × 100
| Mistake | How to Avoid It |
|---|---|
| Forgetting to convert cm³ to dm³ | Always check: if the volume is given in cm³, divide by 1000 |
| Not showing working | ALWAYS write the formula, substitution and answer — even if you can do it in your head |
| Rounding too early | Keep full calculator values until the final answer, then round to an appropriate number of significant figures |
| Missing units | Always state units: mol, g, mol/dm³, g/dm³, kJ/mol |
| Using the wrong Ar values | Always use values given in the question, not ones from memory |
| Confusing mass and moles | Mass is in grams (g); moles is a count (mol). They are different quantities. |
Exam Tip: On the AQA exam, the number of marks for a calculation tells you how many steps the examiner expects to see. A 3-mark calculation needs three visible steps: formula, substitution, answer.
Graph questions appear on almost every paper. Here is what you need to master:
Gradient = change in y ÷ change in x
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