Unit 2: Molecular interactions and reactions

Gas behaviour. States the assumptions of the kinetic theory of gases, derives Boyle's, Charles's and Gay-Lussac's laws qualitatively from particle behaviour, and works through combined gas law problems of the kind QCAA poses in EA Paper 1.

PV = nRT. Sets out the ideal gas equation with QCAA's preferred units, derives molar volume at standard laboratory conditions (24.79 L/mol at SLC), and works through calculations linking pressure, volume, temperature and amount of gas.

Gas stoichiometry. Sets out the four-step mole map for reactions with gas reactants or products, applies the molar volume at SLC and the ideal gas equation, and works through limiting-reactant and percent-yield calculations of the type QCAA poses in EA short response.

Acidity. Defines acids and bases qualitatively, introduces the pH scale and Kw, distinguishes strong from weak acids by extent of ionisation, calculates pH of strong acid and base solutions, and writes balanced equations for acid reactions with active metals, metal carbonates and metal hydroxides.

Water as a solvent. Explains why water's bent shape and O-H bonds give it a permanent dipole and extensive hydrogen bonding, then walks through ion-dipole solvation of NaCl, hydrogen-bonding solvation of ethanol, and the "like dissolves like" rule with worked exceptions.

Solubility and precipitation. Lists the QCAA solubility rules for common ionic compounds, walks through predicting whether a precipitation reaction occurs when two aqueous solutions are mixed, and shows how to write balanced molecular, complete ionic and net ionic equations.

Solution concentration. Defines mol/L, g/L, percent and ppm; works through interconversions; applies the dilution formula c_1 V_1 = c_2 V_2; and links to solution stoichiometry calculations for reactions in aqueous solution.