Acids, Alkalis & Neutralisation

Acid definition

Substance that releases H⁺ ions in solution

Alkali definition

Soluble base that releases OH⁻ ions in solution

Base definition

Substance that neutralises an acid

pH of acids

Less than 7

pH of alkalis

Greater than 7

pH of neutral solution

7

Strong acid

Fully ionises in water (e.g., HCl)

Weak acid

Partially ionises in water (e.g., ethanoic acid)

Strong alkali

Fully ionises (e.g., NaOH)

Neutralisation

Reaction between acid and base forming salt + water

Neutralisation ionic equation

H⁺ + OH⁻ → H₂O

Acid + metal

Salt + hydrogen

Acid + metal oxide

Salt + water

Acid + metal hydroxide

Salt + water

Acid + metal carbonate

Salt + water + carbon dioxide

Test for CO₂

Turns limewater milky

Salt formed depends on acid

HCl → chlorides, H₂SO₄ → sulfates, HNO₃ → nitrates

Example: HCl + NaOH

NaCl + H₂O

Example: H₂SO₄ + MgO

MgSO₄ + H₂O

Example: HNO₃ + CuCO₃

Cu(NO₃)₂ + H₂O + CO₂

Neutralisation use

Treating indigestion, soil pH control, wastewater treatment