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)
36 total rows in download
| Topic | Common mistake / misconception | Do this instead | Quick check |
|---|---|---|---|
| General | Not using the command word properly (state/describe/explain). | State = short fact; describe = what you observe; explain = reason using chemistry ideas. | Did you match the command word? |
| General | Missing or incorrect units in calculations. | Write units in substitutions and final answers; check they make sense (e.g. g, dm³, mol). | Are units present and correct? |
| General | Rounding too early / wrong significant figures. | Keep extra digits in working; round only at the end unless instructed. | Did you round only at the end? |
| General | Not showing working so method marks are lost. | Write the formula, substitute numbers with units, then calculate clearly. | Did you show formula + substitution + working? |
| Particles & states | Saying particles 'expand' when heated (instead of moving faster / further apart). | Heating increases kinetic energy; particles move faster and (in gases) further apart. | Did you mention kinetic energy and spacing/motion correctly? |
| Particles & states | Confusing melting and boiling (or describing temperature change during a change of state). | During melting/boiling, temperature stays constant while energy breaks intermolecular forces. | Did you keep temperature constant during the phase change? |
| Separation | Using filtration for dissolved solids. | Filtration removes insoluble solids; use evaporation/crystallisation for soluble solids. | Is the solid soluble or insoluble? |
| Separation | Distillation vs evaporation confusion. | Distillation collects a solvent/liquid by boiling + condensation; evaporation leaves solute behind. | Are you trying to collect the solvent or the solute? |
| Atoms & structure | Confusing atoms, molecules and ions. | Atoms are neutral particles; molecules are bonded atoms; ions are charged particles. | Is the particle charged or neutral? |
| Atoms & structure | Isotopes vs ions confusion. | Isotopes differ in neutrons; ions differ in electrons (charge). | Is the change neutrons or electrons? |
| Periodic table | Group number vs period number mixed up. | Group = number of outer-shell electrons; period = number of electron shells. | Did you link group to outer electrons and period to shells? |
| Periodic table | Trends explained without particle reasoning (e.g. 'more reactive' with no why). | Use electron shells, shielding, nuclear charge and electron transfer to explain trends. | Did you mention electron transfer/attraction and shielding? |
| Bonding | Ionic vs covalent bonding confusion (especially electron transfer/sharing). | Ionic: electrons transferred → ions attract. Covalent: electrons shared between atoms. | Did you state transfer (ionic) or sharing (covalent)? |
| Bonding | Dot-and-cross diagrams: wrong electron count for ions or missing brackets/charges. | Show correct outer electrons after transfer; put ions in brackets with charges. | Do your ions have full outer shells and correct charges? |
| Bonding | Explaining melting/boiling points without mentioning bonding/forces. | Ionic/giant covalent: strong bonds; simple molecular: weak intermolecular forces; metals: metallic bonding. | Did you link property to bonding/forces? |
| Bonding | Assuming graphite conducts because it has 'strong bonds'. | Graphite conducts due to delocalised electrons between layers; diamond doesn’t. | Did you mention delocalised electrons for graphite? |
| Stoichiometry | Mole calculations: using Mr where Ar is needed (or vice versa). | Use Ar for elements and Mr for compounds. Check formula first. | Is it an element or a compound? |
| Stoichiometry | Not balancing the equation before using ratios. | Balance first, then use coefficients for mole ratios. | Is the equation balanced before calculations? |
| Stoichiometry | Gas volume at r.t.p.: using wrong molar volume or wrong units. | At r.t.p., 1 mol gas = 24 dm³ (use consistent units). | Did you use 24 dm³ mol⁻¹ at r.t.p.? |
| Stoichiometry | Concentration: confusing cm³ and dm³ in (c = n/V). | Convert cm³ to dm³: divide by 1000 before using (V) in dm³. | Did you convert cm³ to dm³? |
| Stoichiometry | Limiting reagent: assuming the first reactant is limiting. | Calculate moles of each; divide by coefficient; smallest value limits. | Did you compare against coefficients to find the limiting reagent? |
| Acids & bases | pH scale: thinking pH 0 is neutral or pH 14 is most acidic. | pH 7 neutral; lower pH more acidic; higher pH more alkaline. | Is pH 7 neutral and acidity increases as pH decreases? |
| Acids & bases | Strong vs concentrated confusion. | Strong = fully ionised; concentrated = high amount per volume (can be weak but concentrated). | Are you talking about ionisation or amount per volume? |
| Acids & bases | Neutralisation: forgetting salt formation depends on reactants. | Acid + base → salt + water; acid + metal → salt + hydrogen; acid + carbonate → salt + CO₂ + water. | Does your product set match the reactants? |
| Salts | Solubility rules not applied when choosing preparation method. | Insoluble salts: precipitation. Soluble salts: titration or excess solid + filtration. | Is the salt soluble or insoluble? |
| Redox | Oxidation/reduction defined only as 'gain/lose oxygen' and misapplied. | Use electron transfer: oxidation = loss of electrons; reduction = gain of electrons. | Did you identify electron loss/gain correctly? |
| Reactivity series | Predicting displacement without using reactivity order. | A more reactive metal displaces a less reactive metal from its compound. | Is the displacing metal higher in the reactivity series? |
| Electrolysis | Cathode vs anode confusion (or ion charges). | Cathode is negative: cations gain electrons (reduction). Anode is positive: anions lose electrons (oxidation). | Did cations go to cathode and anions to anode? |
| Electrolysis | Aqueous electrolysis: forgetting water competes (H⁺/OH⁻). | In aqueous solutions, H⁺/OH⁻ can be discharged; use reactivity/selective discharge rules. | Did you consider H⁺/OH⁻ in aqueous electrolysis? |
| Energetics | Exothermic/endothermic sign confusion in energy level diagrams. | Exothermic releases energy: products lower than reactants. Endothermic absorbs: products higher. | Are products lower (exo) or higher (endo) than reactants? |
| Rates | Saying catalysts 'increase collisions' without 'lower activation energy'. | Catalysts provide an alternative pathway with lower activation energy. | Did you mention lower activation energy? |
| Rates | Rate graphs: mixing up gradient and height. | Rate at a time = gradient of curve (tangent), not the y-value. | Did you use the gradient/tangent for rate? |
| Organic chemistry | Homologous series: not stating general formula or functional group. | State functional group + general formula + similar chemistry (differ by CH₂). | Did you mention functional group and CH₂ difference? |
| Organic chemistry | Alkanes vs alkenes confusion (saturated vs unsaturated). | Alkanes: single bonds, saturated. Alkenes: C=C, unsaturated, decolourise bromine water. | Is there a C=C double bond? |
| Organic chemistry | Drawing displayed structures with wrong number of bonds (carbon valency). | Carbon forms 4 bonds; check each atom’s valency (H=1, O=2, N=3). | Does every carbon have 4 bonds? |
| Organic chemistry | Polymerisation: mixing addition and condensation ideas. | Addition polymerisation: alkene monomers add with no small molecule lost. | Is an alkene double bond opening with no by-product? |
It is a downloadable list of frequent misconceptions and mark-losing mistakes in IGCSE Chemistry (0620), paired with a short fix and a “quick check” prompt.
It covers common mistakes across core 0620 areas, including particles and separation, atomic structure and periodic trends, bonding, stoichiometry, acids and bases/salts, redox and electrolysis, energetics and rates, and organic chemistry.
No. It is a practical revision resource summarising recurring error patterns and mark-scheme expectations. Always verify definitions, equations, and command words against your official syllabus and mark schemes.
Before a paper, skim the topics you are revising. After marking, identify which mistakes you made and practise 5–10 similar questions, using the “quick check” prompts to avoid repeating them.