Unit 2: How do chemical reactions shape the natural world?

Redox in aqueous solution. Covers the rules for assigning oxidation numbers, identification of oxidant and reductant, the half-equation balancing procedure in acidic solution (electrons, then H2O for O, then H+ for H), and combining half-equations into a balanced overall ionic equation.

Concentration and acid-base chemistry. Covers concentration units (mol L^-1, g L^-1, %m/v, %m/m, %v/v, ppm) and dilution calculations, the Brønsted-Lowry model with conjugate acid-base pairs, strong vs weak and concentrated vs dilute, and the calculation of pH from [H+].

Chemistry of water. Covers hydrogen bonding and how it explains water's anomalous physical properties, how water dissolves ionic and polar molecular substances, the use of solubility rules to predict precipitation, and writing balanced ionic and net ionic equations.

Four classic acid reactions. Covers acid plus metal (redox, hydrogen gas), acid plus metal oxide (neutralisation, salt and water), acid plus metal hydroxide (neutralisation, salt and water) and acid plus carbonate or hydrogen carbonate (salt, water and carbon dioxide), with balanced equations and the underlying mechanisms.

Strength of acids and bases. Covers the extent of ionisation as the defining criterion for strong vs weak, the ionisation constants Ka and Kb, how to compare strengths using pKa and pKb, and the inverse relationship between an acid and its conjugate base.

Metal reactivity series and displacement reactions in aqueous solution. Covers the ordering of common metals, the prediction of whether a displacement will occur, the half-equations for the redox process, and the reactions of metals with water, acids and oxygen.

Writing balanced full, ionic and net ionic equations for aqueous reactions. Covers precipitation, neutralisation and metal displacement reactions, the rules for splitting (aq) species, the role of spectator ions, and consistent use of state symbols.

Water polarity and intermolecular forces in aqueous solutions. Covers the bent shape and dipole of water, hydrogen bonding versus dipole-dipole versus dispersion forces, the like-dissolves-like rule, and how to rank the relative solubility of polar, ionic and non-polar substances in water.

Stoichiometry of aqueous reactions. Covers the use of n = cV with concentration in mol per litre, the limiting-reagent decision, the calculation of mass or concentration of products from a balanced equation, and percentage yield in a solution context.

Volumetric analysis. Covers acid-base and redox titrations, primary and secondary standards, the choice of indicator from titration curves, the c1V1 / c2V2 / mole-ratio workflow, and back-titration for samples that react slowly or with excess.

Gravimetric analysis. Covers the choice of precipitating reagent, the lab steps (precipitation, filtration, washing, drying to constant mass), the stoichiometric calculation from precipitate mass to analyte amount, and the common sources of error in a gravimetric determination.

Instrumental analysis. Covers the principles of colorimetry and UV-visible spectroscopy with the Beer-Lambert relationship, the use of calibration curves, and atomic absorption spectroscopy (AAS) for trace-metal analysis, with a comparison of techniques.

Choosing analytical techniques for water-quality testing. Compares gravimetric analysis, volumetric analysis (titration), colorimetry, UV-visible spectroscopy and atomic absorption spectroscopy on the basis of detection limit, accuracy, cost, sample type and analyte concentration.