How to Score Higher in OCR A Level Chemistry A (H432)

• •For Kp: use a RICE table; write mole fractions, then partial pressures, before substituting into the Kp expression — never use square brackets
• •For mc∆T: m is the mass of the solution (not the solute); label it explicitly before substituting
• •For ∆G: convert ∆S from J mol–1 K–1 to kJ mol–1 K–1 (divide by 1000) before combining with ∆H in kJ mol–1
• •For Born–Haber cycles: draw the cycle before calculating; mark each arrow with its enthalpy term and correct sign; check mole ratios (e.g. 2 × atomisation for Cl2 → 2Cl)

• •For electrophilic substitution of benzene: show only four sides of the delocalised ring in the carbocation intermediate (two electrons have left to form the new bond)
• •For nucleophilic addition to carbonyls: the first arrow goes from the nucleophile lone pair to the δ+ carbon, not to the oxygen
• •For radical substitution: initiation (homolytic fission), propagation (two steps), termination (three steps) — include all three termination steps for full marks
• •Cross out and redraw rather than erasing — a rubbed-out structure that leaves ghost lines cannot be marked

• •Always check that the proposed structure matches the molecular formula — a pentavalent carbon or missing substituent immediately fails
• •Do not force data to fit a pre-selected structure; let the evidence lead to the structure
• •For the 1H NMR data sheet: note the caveat that CH adjacent to electron-withdrawing groups on both sides may shift further downfield than expected
• •Draw and cross out candidate structures as you reason — do not leave rejected structures uncrossed as examiners cannot tell which is your final answer

• •Preparing a standard solution: dissolve in a beaker → transfer to correctly-sized volumetric flask → rinse beaker and rod with distilled water and add rinsings → make up to the graduation mark → invert to mix
• •Purifying an organic liquid: use a separating funnel (not a conical flask) → identify layers using density data → dry with anhydrous salt → filter → distil at the boiling point of the pure compound
• •Recrystallisation (organic solid): dissolve in minimum hot solvent → hot-filter → cool slowly → filter under suction → dry the crystals
• •Titration: use two concordant titres (within 0.10 cm3) to calculate the mean — do not include the rough titre in the mean

• •For transition metal definitions: include d-block element (highest-energy electron in a d subshell), transition element (forms at least one ion with an incomplete d subshell), and give electronic configurations for Cr and Cu explicitly
• •For rate order: use the half-life approach (read two consecutive half-lives from the graph; if constant, first order) OR compare initial rates from the data table, showing the numerical ratios
• •For structure and bonding: name the lattice type ('giant metallic', 'giant covalent', 'simple molecular'), describe the bonding, and explicitly link bond/force strength to the magnitude of the melting point
• •Use specific chemical names and formulae — vague references to 'particles' or 'energy' without identifying the substance score Level 1 at best

Give a specific, factual answer with no explanation required — a name, formula, value, or one-line definition.

Give the key features, steps, or observations in sequence — for practical procedures, for graph trends, or for what is seen in a test.

Give chemical reasons for an observation or trend — link cause to mechanism to effect.

Work out a numerical answer, showing every step with quantities labelled and units stated.

Apply chemical principles to a novel or unfamiliar situation not explicitly covered in the specification.

Reach a conclusion by reasoning from data or information given in the question.

Derive a printed numerical result through explicit calculation — the answer is given; you must demonstrate the working that produces it.

Give a brief account covering the main points without full detail — often used for synthesis routes or procedures.