Download clean, printable lists of the most common mistakes students make — so you can fix them before they cost marks.
Each sheet is aligned to its exam board and built from recurring student errors highlighted in examiner reports and mark schemes.
What you get
A topic-by-topic mistakes list with a “do this instead” fix and a quick self-check.
How to use it
Review before past papers, then use the quick checks to catch errors under timed conditions.
Why it works
Many marks are lost on predictable slips: rounding, sign errors, units, and misreading commands.
Coverage by topic
Preview (up to 5 per topic)
38 total rows in download
| Topic | Common mistake / misconception | Do this instead | Quick check |
|---|---|---|---|
| Atomic structure | Confusing mass number with atomic number. | Atomic number = protons; mass number = protons + neutrons. | Which one equals electrons in a neutral atom? |
| Periodic table | Group vs period confused. | Group = columns (similar properties); period = rows (shells). | Are you counting across or down? |
| Bonding | Saying ionic bonds ‘share’ electrons. | Ionic = transfer of electrons; covalent = sharing. | Is it metal + non-metal? |
| Bonding | Metallic bonding described as ‘ionic between metal atoms’. | Positive ions in a sea of delocalised electrons. | Did you mention delocalised electrons? |
| Bonding | Diamond vs graphite properties with wrong structure claim. | Diamond: tetrahedral, hard, no free electrons; graphite: layers, delocalised electrons between layers. | Which allotrope conducts? |
| Equations | Unbalanced symbol equations accepted in your head only. | Balance atom-by-atom; add state symbols if required. | Do atom counts match on both sides? |
| Stoichiometry | Mr calculated using atomic numbers not Ar. | Sum Ar values for each element in the formula. | Did you use the periodic table Ar? |
| Moles | Using mass ÷ wrong divisor (Ar vs Mr confused). | Moles = mass ÷ Mr (or for atoms: mass ÷ Ar). | Which Mr belongs in the denominator? |
| Concentration | Forgetting to convert dm³ ↔ cm³. | 1 dm³ = 1000 cm³; concentration often mol/dm³. | Did you divide cm³ by 1000? |
| Titration | Endpoint described as ‘when it goes pink’ with no mention of indicator role. | Explain colour change when acid/base fully neutralised for that titre. | Did you name the indicator context? |
| Acids & bases | pH described as a measure of ‘strength’ only. | pH relates to H⁺ concentration; strong/weak is about degree of ionisation. | Did you distinguish strength from pH? |
| Neutralisation | Salt formula wrong for common acids (sulfate vs chloride). | Track ion charges: balance positive and negative ions to get formula. | Is the salt charge-neutral? |
| Electrolysis | Cathode/anode products without referring to ion discharge rules. | Apply reactivity series for molten vs aqueous; state which ions reduced/oxidised. | Did you state at which electrode each product forms? |
| Electrolysis | Half-equations with electrons on wrong side. | Reduction gains electrons; oxidation loses electrons. | Do atoms balance as well as charge? |
| Energy changes | Exothermic described as ‘energy is created’. | Energy transferred to surroundings; bonds broken/formed with net release. | Did you avoid ‘created/destroyed’? |
| Reversible reactions | Equilibrium means ‘equal amounts of reactants and products’. | Forward and reverse rates equal; amounts can differ. | Did you mention rates equal? |
| Le Chatelier | Predicting shift without naming what stresses the system. | Identify change (concentration, pressure, temp); state shift opposing change. | Did you mention closed system equilibrium? |
| Rates | Sketchy collision theory with no mention of activation energy. | Particles collide with sufficient energy and correct orientation. | Did you link temperature to particle energy distribution? |
| Catalysts | Catalyst appears in final balanced equation as reactant. | Lower activation energy; not consumed overall. | Did you omit catalyst from stoichiometry? |
| Organic chemistry | Functional groups: naming alcohol/alkene incorrectly from structure. | Identify longest chain, functional group position, suffix/prefix rules. | Is the lowest number used for the functional group? |
| Organic | Combustion products of hydrocarbons incomplete when air limited. | Complete combustion → CO₂ + H₂O; incomplete can produce CO (and C). | Did the question mention limited air? |
| Organic | Polymers: monomer drawn with wrong double bond for addition polymerisation. | Show breaking of π bond to form repeating unit links. | Does repeat unit match the monomer pattern? |
| Separation | Chromatography Rf > 1 possible. | Rf = distance spot ÷ distance solvent (same baseline; always ≤ 1). | Is denominator solvent front? |
| Analysis | Flame tests: mixing up sodium and potassium without cobalt glass mention. | Use cobalt glass for potassium yellow interference with sodium. | Which metal was present as contaminant? |
| Atmosphere | Greenhouse effect confused with ozone hole as the same issue. | Greenhouse: IR absorption; ozone: UV protection at stratosphere — different processes. | Which layer/gas did the question name? |
| Life-cycle / sustainability | LCA only as ‘bad for environment’ with no evidence. | Reference extraction, manufacture, use, disposal impacts as appropriate. | Did you name at least two lifecycle stages? |
| Practical skills | Burette readings taken from top meniscus for solutions. | Read bottom of meniscus at eye level for liquids like water. | Did you mention eye level? |
| Uncertainty | Claiming perfect accuracy from one trial. | Repeat and compare concordant titres; use mean of concordant. | Did you repeat at least twice? |
| Graphs | Line of best fit drawn to hit every point. | Balance points above/below; ignore anomaly if identified. | Is there one clear outlier? |
| Ions | Writing electron configuration of ions without adjusting electrons. | Add/remove electrons; noble gas shorthand; check charge on ion. | Does the ion’s electron total match its charge? |
| Patterns | Group 1 reactivity trend explained only as ‘more reactive’ with no electron shell reasoning. | Outer electron further from nucleus / more shielding → easier loss (as you go down). | Did you link structure to trend? |
| Exam technique | State symbols omitted when mark scheme demands them. | (s), (l), (g), (aq) after species in required equations. | Highlight ‘including state symbols’ in the question. |
| Exam technique | Writing narrative instead of ordered bullet when ‘give two reasons’ asked. | Numbered/bulleted two distinct points with specific chemistry. | Are your two points genuinely different? |
| Exam technique | Spelling ‘separate’, ‘occurrence’, ‘apparatus’ wrong in method questions. | Learn high-frequency practical vocabulary for AO2/AO3 practical questions. | Proofread method answers? |
| Calculations | Limiting reagent: using wrong substance after moles calculated. | Compare mole ratios to equation; smallest amount limits product. | Did you divide by coefficients? |
| Acids & metals | Hydrogen test confused with oxygen test. | Splint pops for H₂; relights glowing splint for O₂. | Which gas is being tested? |
| Fuels | Energy density vs specific energy confused. | Match definitions used in the specification context of fuels comparison. | Are you using the phrase from the lesson card? |
| Chemical cells | Current direction without reference to half-cells/electrode polarity at GCSE level. | Link more reactive metal as negative terminal in basic voltaic explanation if taught. | Did you follow the mark scheme diagram labels? |
A revision checklist of typical quantitative slips, equation errors and practical write-up wording problems for AQA-style questions.
Question contexts and command expectations differ by board. This list targets AQA GCSE Chemistry (8462) phrasing; cross-check with your tier and the equations you are given in the exam.