Acids and bases are two of the most fundamental classes of chemicals in chemistry. Understanding their properties, reactions, and the pH scale is tested in almost every WAEC Chemistry paper.
Properties of acids
• pH < 7 • Taste sour (do NOT test by tasting in a lab) • Turn blue litmus RED • React with metals to produce hydrogen gas: Zn + H₂SO₄ → ZnSO₄ + H₂ • React with carbonates to produce CO₂: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ • Common acids: HCl (hydrochloric), H₂SO₄ (sulfuric), HNO₃ (nitric), CH₃COOH (acetic/vinegar)
Properties of bases
• pH > 7 • Taste bitter, feel soapy (do not test!) • Turn red litmus BLUE • Soluble bases are called ALKALIS • React with acids in a neutralisation reaction • Common bases: NaOH (sodium hydroxide), Ca(OH)₂ (calcium hydroxide), NH₃ (ammonia)
Neutralisation and salt formation
Acid + Base → Salt + Water Example: HCl + NaOH → NaCl + H₂O The salt formed depends on the acid and base: • HCl → chloride salts • H₂SO₄ → sulfate salts • HNO₃ → nitrate salts Indicators: Litmus (red in acid, blue in base), Universal indicator (shows pH by colour), Phenolphthalein (colourless in acid, pink in base).
Key points
- Acids: pH < 7, red litmus, sour
- Bases: pH > 7, blue litmus, bitter
- Neutralisation: acid + base → salt + water
- Salt name = metal name + acid radical
- Universal indicator shows exact pH
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WAEC tip
Remember the mnemonic: 'Red is for Acid, Blue is for Base.' WAEC always tests this in Paper 1. Get the litmus colours wrong and you lose easy marks.
Practise this
Write the balanced equation for the reaction between sulfuric acid and sodium hydroxide. Name the salt formed and state its pH.
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