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)
42 total rows in download
| Topic | Common mistake / misconception | Do this instead | Quick check |
|---|---|---|---|
| General | Not using the command word correctly (state/describe/explain). | State = short fact; describe = what you observe; explain = reason with chemistry. | Did you match the command word? |
| General | Using vague phrases that don’t earn marks in Edexcel mark schemes (e.g. 'pollution', 'weather', 'it reacts'). | Be specific: name the chemical/ion/process and the direction of change (e.g. 'fewer successful collisions', 'lower activation energy'). | Is your explanation specific and chemistry-based? |
| General | Missing units / wrong significant figures in calculations. | Include units in working; round at the end to the required s.f. | Are units present and s.f. correct? |
| General | Not balancing equations before mole ratio calculations. | Balance first; then use coefficients as mole ratios. | Is the equation balanced first? |
| General | State symbols missing or incorrect in equations (s, l, g, aq). | Include correct state symbols, especially for aqueous ions and gases. | Are state symbols correct and included where required? |
| Atomic structure | Isotope vs ion confusion. | Isotopes differ in neutrons; ions differ in electrons (charge). | Is the change neutrons or electrons? |
| Periodic table | Trends explained without particle reasoning. | Use electron shells, shielding, nuclear charge, and electron transfer to explain trends. | Did you mention electron transfer/attraction and shielding? |
| Bonding | Ionic vs covalent confusion (transfer vs sharing). | Ionic: electron transfer → ions. Covalent: electrons shared. | Did you state transfer (ionic) or sharing (covalent)? |
| Bonding | Explaining properties without linking to bonding/forces. | Relate melting/boiling point, conductivity, hardness to bonding and structure. | Did you link to bonding/structure? |
| Bonding | Ionic equations: writing spectator ions in the net ionic equation. | Cancel spectator ions to write the net ionic equation only. | Did you remove spectator ions? |
| Bonding | Covalent structures: calling intermolecular forces 'bonds' within a molecule. | Covalent bonds are within molecules; forces between molecules are intermolecular. | Did you distinguish bonds vs intermolecular forces? |
| Bonding | Conductivity: saying solid ionic compounds conduct electricity. | Solid ionic compounds do not conduct because ions are not free to move; molten/aqueous do. | Are ions free to move in the state given? |
| Stoichiometry | Using Ar where Mr is needed (or vice versa). | Use Ar for elements; Mr for compounds; check formula carefully. | Element or compound? |
| Stoichiometry | Concentration: mixing cm³ and dm³ in (c=n/V). | Convert cm³ to dm³ (÷1000) before using volume in dm³. | Did you convert cm³ to dm³? |
| Stoichiometry | Empirical formula: not converting masses to moles first. | Convert each element mass to moles, then divide by the smallest to get ratios. | Did you convert to moles and simplify ratios? |
| Stoichiometry | Empirical formula: forgetting to multiply to whole numbers (e.g. 1.5 ratios). | If ratios are fractional, multiply all by the same factor to get whole numbers. | Did you convert ratios to whole numbers? |
| Stoichiometry | Limiting reagent guessed rather than calculated. | Compare moles against coefficients; smallest value limits. | Did you compare with coefficients? |
| Acids & bases | Strong vs concentrated confusion. | Strong = fully ionised; concentrated = high amount per volume. | Ionisation or amount per volume? |
| Acids & bases | Neutralisation products wrong (missing CO₂ for carbonates). | Acid + carbonate → salt + CO₂ + water; acid + base → salt + water. | Do products match reactants? |
| Acids & bases | pH: thinking pH 0 is neutral or pH 14 is most acidic. | pH 7 is neutral; lower pH is more acidic; higher pH is more alkaline. | Is pH 7 neutral and acidity increases as pH decreases? |
| Acids & bases | Indicator colours mixed up (acid vs alkali). | Learn the colour changes for common indicators used in the specification. | Have you matched the correct indicator colour to pH? |
| Salts | Using the wrong preparation method (soluble vs insoluble). | Insoluble salts: precipitation. Soluble salts: titration or excess solid + filtration. | Is the salt soluble? |
| Salts | Crystallisation method missing key steps (e.g. not filtering first, unclear drying method). | If a solid impurity is present: filter first. Concentrate to near saturation, cool to crystallise, filter crystals, then dry on filter paper. | Did you include filter → concentrate → cool → filter → dry? |
| Redox | Oxidation/reduction mixed up. | Oxidation = loss of electrons; reduction = gain of electrons. | Which species loses electrons? |
| Electrolysis | Cathode/anode confusion and incorrect ion discharge. | Cathode: reduction (gain e⁻). Anode: oxidation (lose e⁻). Consider H⁺/OH⁻ in aqueous solutions. | Did you apply reduction at cathode, oxidation at anode? |
| Electrolysis | Aqueous electrolysis: ignoring H⁺/OH⁻ competing for discharge. | In aqueous solutions, water provides H⁺/OH⁻; use selective discharge rules. | Did you consider H⁺/OH⁻ for aqueous solutions? |
| Electrolysis | Redox at electrodes: swapping oxidation/reduction. | Reduction at cathode (gain e⁻); oxidation at anode (lose e⁻). | Cathode = reduction; anode = oxidation? |
| Energetics | Exothermic/endothermic sign confusion in energy diagrams. | Exothermic: products lower than reactants. Endothermic: products higher. | Are products lower (exo) or higher (endo)? |
| Rates | Catalysts described as increasing collisions but not lowering activation energy. | Catalysts provide an alternative pathway with lower activation energy. | Did you mention activation energy? |
| Rates | Rate graphs: using the y-value instead of gradient to find rate at a time. | Rate at a time = gradient of curve (tangent). | Did you use the gradient/tangent? |
| Rates | Graph reading: misreading scales or rounding incorrectly at the end. | Check axis increments first; only round your final value to the required accuracy. | Did you confirm the axis scale and round at the end? |
| Rates | Collision theory: missing the idea of successful collisions (enough energy + orientation). | Explain rate changes via frequency of successful collisions and activation energy. | Did you mention successful collisions/activation energy? |
| Organic chemistry | Confusing alkanes and alkenes (saturated vs unsaturated). | Alkenes have C=C and decolourise bromine water; alkanes do not. | Is there a C=C double bond? |
| Organic chemistry | Displayed formula bonds incorrect (carbon valency). | Carbon forms 4 bonds; check valency of each atom. | Does each carbon have 4 bonds? |
| Organic chemistry | Functional groups: confusing alcohols, carboxylic acids and esters. | Recognise key groups: –OH (alcohol), –COOH (carboxylic acid), –COO– (ester). | Did you identify the functional group correctly? |
| Organic chemistry | Homologous series: not stating general formula / difference of CH₂. | State functional group, general formula and that successive members differ by CH₂. | Did you mention CH₂ difference and functional group? |
| Corrosion | Naming rust incorrectly (e.g. iron(II) oxide). | Rust is hydrated iron(III) oxide (not iron(II) oxide). | Did you give the correct full name for rust? |
| Experimental skills | Describing diffusion/rate processes without particle reasoning (random motion/collisions). | Use particle model language: random motion, collisions with air particles, different speeds due to molar mass. | Did you mention particle motion/collisions rather than just 'rate'? |
It is a downloadable list of frequent misconceptions and mark-losing mistakes in Edexcel IGCSE Chemistry (4CH1), paired with a short fix and a “quick check” prompt.
It covers common mistakes across the main 4CH1 areas: bonding and structure, quantitative chemistry, acids and bases, 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 Edexcel specification and mark schemes.
Before a paper, skim the topic you’re revising. After marking, identify which mistakes you made and practise 5–10 similar questions using the “quick check” prompts to avoid repeating them.