Electrochemistry and Redox Reactions
What you must know
Identify oxidation (loss of electrons, increase in oxidation number) and reduction (gain). Balance redox equations by half-reaction and oxidation-number methods. Understand galvanic versus electrolytic cells, anode and cathode conventions (oxidation at anode, reduction at cathode in both), standard electrode potentials, and cell EMF = E°cathode − E°anode. Know electrolysis products, Faraday's laws and applications such as electroplating and corrosion.
Traps
- Confusing anode and cathode in galvanic versus electrolytic cells.
- Reversing the sign convention for electrode potentials.
- Forgetting to balance atoms and charge in half-reactions.
- Mixing up oxidation-number changes with electron count.
Worked example
For a Zn/Cu cell: E°(Cu²⁺/Cu) = +0.34 V, E°(Zn²⁺/Zn) = −0.76 V. EMF = 0.34 − (−0.76) = +1.10 V. Copper is reduced (cathode), zinc oxidised (anode). Rule of thumb: the more positive reduction potential is reduced; EMF = E°cathode − E°anode.
Organic Chemistry: Hydrocarbons and Functional Groups
What you must know
Recognise homologous series, functional groups and IUPAC naming for alkanes, alkenes, alkynes, arenes, alcohols, aldehydes, ketones, carboxylic acids, esters, amines and halogenoalkanes. Know addition, substitution, elimination, oxidation and esterification reactions, and the tests that distinguish functional groups (bromine water, Tollens' and Fehling's reagents, sodium carbonate). Understand isomerism: chain, position, functional group and stereoisomerism.
Traps
- Naming with the wrong suffix or ignoring the principal functional group.
- Confusing aldehydes and ketones in Tollens'/Fehling's tests (only aldehydes react positively).
- Forgetting Markovnikov's rule in addition to alkenes.
- Mixing substitution (alkanes) with addition (alkenes).
Worked example
Distinguish ethanal from propanone. Ethanal gives a silver mirror with Tollens' reagent and a red precipitate with Fehling's; propanone does neither because it lacks the –CHO group. Rule of thumb: aldehydes are oxidised easily; ketones resist mild oxidation.
Laboratory Practice, Safety and Chemical Calculations
What you must know
Understand safe handling, hazard symbols, and correct use of apparatus (burette, pipette, volumetric flask, balance). Know good technique: rinsing glassware, reading meniscus at eye level, weighing by difference, and recording significant figures consistent with instrument precision. Apply error analysis - systematic versus random, precision versus accuracy - and calculate percentage error and percentage yield. Recognise appropriate separation methods (filtration, distillation, crystallisation, chromatography) and titration technique.
Traps
- Rinsing a pipette with the solution to be measured (correct) versus rinsing a burette with water (incorrect).
- Reporting too many significant figures.
- Confusing precision with accuracy.
- Forgetting to subtract the container mass when weighing.
Worked example
A 25.0 cm³ pipette delivers a solution titrated against 0.100 mol dm⁻³ NaOH; the average titre is 24.60 cm³. Moles NaOH = 0.02460 × 0.100 = 2.46 × 10⁻³ mol. For a 1:1 stoichiometry the acid concentration is 2.46 × 10⁻³/0.0250 = 0.0984 mol dm⁻³. Rule of thumb: average concordant titres (within 0.10 cm³) before calculating, and carry units throughout.