An interactive companion resource that covers Achievement Standard 91392 - Demonstrate understanding of equilibrium principles in aqueous systems, from NCEA Level 3 Chemistry. The first chapter covers sparingly soluble salts, precipitates and solutions with common ions. The second chapter revises acids and bases and calculating pH, extending the calculations to weak acids and bases too. The third chapter investigates buffer systems, how to make them and a range of calculations. The final chapter introduces titration curves, the key considerations and calculations.