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LearnCambridge06202026–2028Papers 1, 3 · CoreAcids, bases and salts

Papers 1, 3 · Module

Acids, bases and salts

3 subtopics≈ 110 min in total

Start the module: Acids, bases and pH Open graphing calculator

Acids, bases and pH
Acids release $\mathrm{H^+}$ ions in water (proton donors); pH below 7. Bases neutralise acids (proton acceptors); soluble bases are alkalis, releasing $\mathrm{OH^-}$ , pH above 7. Acids react with metals (→ salt + hydrogen), bases (→ salt + water) and carbonates (→ salt + water + carbon dioxide). Strong acids ionise completely; weak acids only partly.
≈ 40 min
Oxides
Metal oxides are usually basic: they react with acids to form salts. Non-metal oxides are usually acidic: they react with bases, and soluble ones give acidic solutions. Amphoteric oxides ( $\mathrm{Al_2O_3}$ , $\mathrm{ZnO}$ ) react with both acids and bases. Neutral oxides (CO, NO, $\mathrm{N_2O}$ ) react with neither.
≈ 25 min
Preparation of salts
A salt forms when the hydrogen of an acid is replaced by a metal (or ammonium). The acid gives the second part of the name: hydrochloric → chloride, sulfuric → sulfate, nitric → nitrate. Soluble salts are made by adding excess insoluble base, metal or carbonate to acid, filtering, then crystallising; or by titration when using an alkali. Insoluble salts are made by precipitation: mix two solutions, filter, wash and dry.
≈ 45 min