Chemistry
Core concepts
The chemistry paper covers atomic structure, the periodic table, chemical bonding, formulae and equations, moles, acids and bases, and simple organic chemistry. Understand: protons, neutrons and electrons; atomic number versus mass number; isotopes; electron shells and how they explain group and period position; ionic, covalent and metallic bonding; writing and balancing equations; relative atomic mass and the mole concept (n = m/M, Avogadro's number); concentration (c = n/V); pH and neutralisation; oxidation and reduction as electron loss and gain; the reactivity series and displacement reactions; hydrocarbons (alkanes, alkenes) and simple functional groups.
Traps to expect
- Unbalanced equations: every element must balance, and charges must balance in ionic equations.
- Mole arithmetic: molar mass uses atomic masses from the periodic table, and mass must be in grams.
- Confusing atoms, molecules and ions - for example, O₂ is a molecule of two atoms.
- Acid–base language: an acid donates H⁺, a base accepts it; a pH below 7 is acidic, above 7 basic.
- Oxidation state sign errors and mixing up oxidation with reduction (remember OIL RIG: Oxidation Is Loss, Reduction Is Gain of electrons).
Rule of thumb
For any calculation involving amounts, convert mass to moles first, use the balanced equation's coefficients as a mole ratio, then convert back to mass or volume. Round only at the final step.
Worked example
How many moles are in 36 g of water? M(H₂O) = 2(1) + 16 = 18 g/mol, so n = 36/18 = 2 mol. This contains 2 × 6.02 × 10²³ ≈ 1.2 × 10²⁴ molecules.