Acids release hydrogen ions in water: they taste sour, have pH below 7, turn blue litmus red and react with bases, carbonates and metals. Bases/alkalis are bitter, slippery, have pH above 7 and neutralise acids. Both only show their properties when dissolved in water, where they dissociate into ions.
Common acids: organic acids include citric acid (citrus fruits), acetic acid (vinegar), formic acid (ant and bee stings) and lactic acid (sour milk); mineral acids include hydrochloric, nitric and sulphuric acid.
Uses: acids go into fertilisers, explosives, rust removal and food preservation; bases go into soap and cleaning products, water treatment, medicines such as antacids, and soil treatment.
Simple tests: acids turn blue litmus red and bases turn red litmus blue. When an acid and a base react, they neutralise each other to give a salt and water.
Role of water: in water, acids release H⁺ ions and bases release OH⁻ ions. This is why dry hydrogen chloride gas does not change litmus but moist hydrogen chloride does.
Safety: concentrated acids and strong alkalis are corrosive. Never taste laboratory chemicals; the 'sour' experiment uses only safe food acids such as lemon juice or vinegar.
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