Short Summary

Chapter 2, Acids, Bases and Salts, details the chemical behaviours, ionic properties, and classification of acidic, basic, and neutral substances. Acid-base indicators such as purple litmus dye, which is extracted from lichens, turmeric, and the petals of flowers such as Hydrangea, Petunia, and Geranium change colour to indicate whether a solution is acidic or basic. Acids react with bases to produce salt and water in a process known as neutralisation, while metallic oxides react with acids to form salt and water, demonstrating their basic nature. When dissolved in water, acids conduct electricity because they release hydrogen ions (H⁺), which are also present as hydronium ions (H₃O⁺), whereas bases produce hydroxide ions (OH⁻). Diluting an acid or base by dissolving it in water is an exothermic process that decreases the concentration of hydronium ions (H₃O⁺) or hydroxide ions (OH⁻) per unit volume. The pH and nature of salt solutions depend on the strength of the acid and base from which they are formed: a strong acid and a strong base produce a neutral salt with a pH of 7, a strong acid and a weak base produce an acidic salt with a pH below 7, and a strong base and a weak acid produce a basic salt with a pH above 7.