Acids and bases are among the most familiar and widely encountered chemicals in both the laboratory and everyday life, from the citric acid in fruit juice to the alkaline cleaning products under the sink. Yet beneath these familiar examples lies a rich and precise chemistry that this chapter unpacks in detail.

We begin by examining the characteristic properties of acids and bases, looking at how they react with metals, carbonates and each other, and how indicators such as litmus, methyl orange and thymolphthalein can be used to distinguish between them. We then introduce the pH scale as a measure of hydrogen ion concentration, and define neutralisation at the ionic level. For Extended candidates, we go further and introduce the Bronsted-Lowry definitions of acids as proton donors and bases as proton acceptors, and distinguish between strong and weak acids in terms of their degree of dissociation in aqueous solution.

We then classify oxides as acidic, basic or amphoteric, and explore how this relates to the metallic or non-metallic character of the element involved. The chapter closes with the preparation of salts, covering a range of methods including titration, reaction with excess metal, excess insoluble base or carbonate, and precipitation. We also look at solubility rules for common salts, and introduce the concepts of hydrated and anhydrous substances and water of crystallisation.