Acids, bases, and salts cover reactions of acids with metals, bases, and carbonates; the pH scale; salt preparation methods; and practical titration techniques.
Acids: produce H⁺ ions in solution. Common: HCl (hydrochloric), H₂SO₄ (sulfuric), HNO₃ (nitric). Properties: pH < 7, react with metals, carbonates, and bases. Bases: neutralise acids. Alkali: soluble base (produces OH⁻ in solution). Common: NaOH, KOH, Ca(OH)₂. pH scale: 0–14. pH 7 = neutral. Universal indicator/pH meter to measure. Strong acids fully dissociate; weak acids partially dissociate.
Acid + metal → salt + hydrogen (e.g., Mg + 2HCl → MgCl₂ + H₂). Acid + base → salt + water (neutralisation). Acid + carbonate → salt + water + CO₂ (fizzing). Acid + alkali → salt + water. Name of salt: metal name + acid root (HCl → chloride, H₂SO₄ → sulfate, HNO₃ → nitrate).
Soluble salts from insoluble reactant: add excess solid to acid, filter, evaporate. Soluble salts from both soluble reactants: titration method — find exact volumes, mix without indicator, evaporate. Insoluble salts: precipitation — mix two solutions containing the ions, filter the precipitate, wash and dry. Example: BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq).
Strength and concentration are different concepts. A strong acid (e.g., HCl, H₂SO₄) fully dissociates — all its molecules split into ions in solution. A weak acid (e.g., ethanoic acid, citric acid) only partially dissociates. Concentration refers to the amount of acid per unit volume (mol/dm³). You can have dilute strong acid (few moles of HCl in lots of water) or concentrated weak acid (many moles of ethanoic acid). Strength is about the degree of dissociation; concentration is about quantity.
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