SEC Chemistry: Core Syllabus Content
Domain overview
This domain spans the SEC Chemistry syllabus: formulae and moles, bonding and structure, the periodic table, acids, bases and salts, electrolysis, energetics, rates, equilibrium, organic families, and air, water and fuels. The exam tests recall of definitions and tests, application of calculations to unfamiliar data, and particle-level explanations of observations.
Core rules and concepts
- Mole bridge: n = m/Mr; n = cV with V in dm³; one mole of gas occupies about 24 dm³ at r.t.p.
- Balance equations first; correct formulae and state symbols secure method marks.
- Ionic lattices conduct when molten or aqueous, not solid; simple molecules have weak intermolecular forces and low melting points.
- Group I reactivity increases down; Group VII increases up; transition metals form coloured compounds and variable oxidation states.
- Acids donate H⁺, bases accept H⁺; phenolphthalein suits weak acid–strong base, methyl orange strong acid–weak base.
- Electrolysis: cathode reduction, anode oxidation; reactive electrodes dissolve, inert electrodes release gas.
- Homologous series share a general formula and functional group; name from the longest chain.
Worked example
4.8 g magnesium reacts fully with dilute hydrochloric acid. Volume of H₂ at r.t.p.? Mg + 2HCl → MgCl₂ + H₂. n(Mg) = 4.8/24 = 0.20 mol; ratio 1:1, so n(H₂) = 0.20 mol; V = 0.20 × 24 = 4.8 dm³. Reasoning: mass → moles → ratio → gas volume.
Traps
- Using cm³ in cV; convert to dm³ first.
- Quoting gas volume without r.t.p.; molar volume varies with temperature and pressure.
- Confusing empirical with molecular formula; divide by smallest ratio, not by Mr.
- Calling every salt solution neutral; check the parent acid and base.
- Saying cathode is positive in electrolysis; it is negative there but positive in a cell.
- Forgetting a 2:1 ratio such as 2HCl:1H₂; write the ratio explicitly.