Chemistry
This section covers the single Chemistry domain assessed in NZ Scholarship Chemistry. The exam goes beyond Level 3 recall: it asks you to integrate atomic structure, bonding, equilibrium, redox, organic mechanisms and spectroscopy into multi-step problems, and to justify answers with evidence and correct terminology.
Core concepts to master
- Structure and bonding: VSEPR shapes, hybridisation, molecular orbital diagrams for diatomics, and how intermolecular forces explain physical properties.
- Equilibrium and thermodynamics: Kc and Kp expressions, reaction quotient Q versus K, Le Chatelier reasoning, and the links ΔG° = −RT ln K = −nFE°cell.
- Acid–base: Ka/Kb, buffer calculations, titration curves, and indicator choice.
- Redox and electrochemistry: standard electrode potentials, cell notation, and the Nernst equation for non-standard conditions.
- Organic chemistry: functional-group interconversions, mechanisms (SN1/SN2, E1/E2, electrophilic addition and aromatic substitution, carbonyl addition), stereochemistry, and multi-step synthesis.
- Spectroscopy: IR absorptions, 1H and 13C NMR (shift, integration, n+1 splitting), and mass spectra including M+ and isotope patterns.
Worked example
For Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s), E°cell = +1.10 V and n = 2. Find K at 298 K. Use ΔG° = −nFE°cell = −RT ln K, so ln K = nFE°cell/RT. ln K = (2 × 96 485 × 1.10)/(8.314 × 298) = 85.7. K = e^85.7 ≈ 1.6 × 10^37. The large value shows the reaction is strongly product-favoured under standard conditions.
Traps that cost marks
- Using E°cell when concentrations are non-standard; apply the Nernst equation.
- Omitting n or using the wrong sign in ΔG° = −nFE°.
- Drawing curly arrows from an atom with no lone pair or from a σ bond in the wrong direction.
- Predicting NMR splitting from equivalent neighbours rather than non-equivalent ones.
- Giving a numerical answer without units or with unjustified significant figures.