Chemistry rewards precise equation balancing, calculation discipline and organic-mechanism fluency. Here is what an A* candidate does differently across Cambridge, Edexcel and A-Level.
Velocity Tuition Academy · Chemistry · A* Strategy
Updated May 2026·Written by Velocity Tuition Academy·Reviewed by experienced Cambridge CAIE and Edexcel Chemistry tutors
Chemistry is the most reliably learnable A* of the three sciences — the syllabus is precise, the mark schemes are predictable, and the calculation discipline transfers from one topic to the next. But it is also the one where students most commonly stall at a B or A: not because the content is missing, but because equation balancing, mole calculations or organic mechanisms are not yet automatic. This guide explains the exam-specific habits that consistently move students from B to A* across Cambridge IGCSE 0620, Edexcel 4CH1, Cambridge A-Level 9701 and Edexcel International A-Level Chemistry.
An A* in Chemistry assumes that balancing equations is reflexive. A student who slows down to check coefficients in the exam loses time on harder problems. The drill: 20 equations a day for two weeks at the start of the exam term, mixed across acid-base, redox, displacement, combustion, organic synthesis. By the end, balancing is automatic.
The specific patterns to internalise:
Acid + Carbonate → Salt + Water + CO₂. Always.
Acid + Metal Oxide → Salt + Water. Always.
Acid + Reactive Metal → Salt + Hydrogen.
Combustion of hydrocarbon → CO₂ + H₂O. Balance the carbons first, hydrogens second, oxygens last.
Displacement — the more reactive metal/halogen displaces the less reactive from a compound.
Mole Calculations: The Mark Spread is Huge
Mole calculations carry the highest mark density in Chemistry exams. A student who understands them deeply can earn 12-15 marks in 10 minutes on questions that students who guess earn 2-3 on. The relationships to drill until automatic:
n = m / M (moles = mass ÷ molar mass)
n = c × V (moles = concentration × volume in dm³)
n(gas) = V / 24 at room temperature and pressure (in dm³)
Atom economy: (mass of desired product ÷ mass of all products) × 100
The A* habit is to write the equation first, identify the mole ratio from the equation, calculate moles of the known substance, scale to the unknown, then convert back to mass, volume or concentration as required. Show every step. Mark schemes award method marks at each conversion.
Bonding And Structure: Get The Definitions Exact
Bonding questions are where students most commonly lose marks at the top end. Mark schemes are unusually strict:
Ionic bonding — electrostatic attraction between oppositely charged ions, formed by transfer of electrons. Note: "transfer," not "sharing." Many students write the wrong one.
Covalent bonding — shared pair of electrons between two non-metal atoms. The shared pair attracts both nuclei.
Metallic bonding — sea of delocalised electrons surrounding positive metal ions; electrostatic attraction between the positive ions and the delocalised electrons.
Giant covalent (e.g., diamond, graphite, SiO₂) — many strong covalent bonds in a 3D (or layered) network, hence high melting point.
Simple molecular — strong covalent bonds within molecules but weak intermolecular forces between molecules; the weak forces are broken on melting, not the covalent bonds.
The classic mark-loser: explaining why a giant covalent substance has a high melting point. The answer is many strong covalent bonds need to be broken — these require a lot of energy. Not "strong covalent bond."
Organic Chemistry: Mechanism Discipline
At IGCSE, organic content is limited (homologous series, basic functional groups, simple reactions). At A-Level, organic becomes one of the largest topics and rewards a systematic approach:
Curly arrows show electron movement — from a bond or lone pair, to an atom (or to form a new bond). One curly arrow = movement of two electrons. The arrowhead starts and ends at the correct points; sloppy arrows lose marks.
Mechanisms by reaction type — nucleophilic substitution (SN1 vs SN2), nucleophilic addition (to C=O), electrophilic addition (to C=C), electrophilic aromatic substitution, free radical substitution. Each has a standard mechanism that should be drawn from memory.
IUPAC nomenclature — name organic compounds systematically; this is a low-effort, high-mark area that students often skip.
Functional group tests (IGCSE and A-Level) — bromine water for C=C, Tollens' reagent for aldehydes, Fehling's solution, iodoform — drill the reagent, observation and conclusion for each.
Practical Skills And Required Practicals
Both Cambridge and Edexcel assess practical skills heavily. Common practical-skills mark losers:
Apparatus selection — choose the most precise instrument for the measurement (burette for accurate volume, balance for mass, gas syringe for gas volume).
Results tables — column headings with quantity and units in square brackets. Consistent decimal places within a column.
Titrations — concordant titres only (within 0.10 cm³), average of concordant readings, use the moles equation correctly.
Errors and improvements — random vs systematic, practical improvements (insulation, repeats, smaller increments, calibration).
At A-Level, three topics most often separate the A from the A*:
Equilibria — Kc, Kp, Kw, Ka, Kb expressions; predicting shift direction; calculating equilibrium concentrations and partial pressures from initial conditions and Kc. Many students skip the ICE-table method, which is the most reliable way to score full marks.
Energetics — Hess's law, bond enthalpies, lattice enthalpies via Born-Haber cycles, enthalpies of solution. The Born-Haber cycle is a standard mark-magnet that rewards careful drawing.
Electrochemistry — standard electrode potentials, cell potentials, predicting feasibility, redox titrations. The sign convention (E° more positive = species more readily reduced) trips students up; drill it.
Aiming for an A* in IGCSE or A-Level Chemistry?
Our 1-on-1 Chemistry tutors prepare students for Cambridge (0620 / 9701) and Edexcel International — mole calculations, organic mechanisms, energetics, and exam-mark-scheme literacy. Free diagnostic trial.
An A* in IGCSE Chemistry requires four things: automatic equation balancing, fluent mole calculations across mass/volume/concentration, precise bonding-and-structure definitions that match the mark scheme, and consistent practical-skills technique (apparatus, results tables, percentage error). Combined with 10+ timed past papers and a tracked error log, this consistently produces A* outcomes.
A-Level Chemistry A* adds three demanding areas to the IGCSE fundamentals: equilibria (Kc/Kp/Ka calculations using ICE tables), energetics (Born-Haber cycles, Hess's law), and electrochemistry (standard electrode potentials, feasibility). Organic mechanisms with correct curly arrows are also essential — they account for a substantial fraction of A2-paper marks.
Generally yes for students who struggle with quantitative work — A-Level Chemistry has substantial calculation, equilibrium analysis and organic-mechanism content. Biology has more content to memorise but fewer calculations. For students strong in maths and visual-spatial reasoning, Chemistry can be easier than Biology because the structure is more systematic.
For IGCSE Chemistry A*: 5-7 hours a week in the year of the exam, rising in the final term. For A-Level Chemistry A*: 8-10 hours a week across two years, with the heaviest load in the second year where the A* is decided. Daily 30-minute equation-balancing and mole-calculation drills are highly effective.
Both cover the same major topics: atomic structure, bonding, stoichiometry, energetics, rates, equilibria, acids/bases, redox, organic chemistry. Cambridge 0620 emphasises extended explanation questions. Edexcel 4CH1 has marginally more structured calculation questions and slightly different practical-skills emphasis. Difficulty is comparable; choice usually follows the school.
Strongly recommended, almost universally required. A-Level Chemistry builds directly on IGCSE foundations (mole calculations, bonding, basic organic). Students starting A-Level without IGCSE Chemistry need substantial catch-up in the first term. Most schools require IGCSE Chemistry at grade 6 / B or above for A-Level entry.
