Strong Acids

Sodium hydroxide

Strong Acids

• Strength of an acid – the degree of ionisation or dissociation of the acid in water.
• Strong acid – an acid which ionises / dissociates completely in water to form high concentration of hydrogen ions (H⁺).
• Example of strong acid: Mineral acid – hydrochloric acid (HCl), nitric acid (HNO₃) and sulphuric acid (H₂SO₄).
• Example of the strong acid reaction in water: HCl(aq) –> H⁺(aq) + Cl^-(aq)  (The concentration of hydrogen ions is equal to the concentration of hydrochloric acid)

Weak Acids

• Weak acid – an acid which ionises / dissociates partially in water to form low concentration of hydrogen ions (H⁺).
• Example of weak acid: ethanoic acid (CH₃COOH) and methanoic acid (HCOOH)
• Example of the weak acid reaction in water: CH₃COOH <—-> CH₃COO^-(aq) + H⁺(aq) {The concentration of hydrogen ions is low and the ions (CH₃COO^- and H⁺) reacts to reform the ethanoic acid molecule = reversible reaction}

Strong Alkalis

• Strength of an alkali – the degree of ionisation or dissociation of the alkali in water.
• Strong alkali – an alkali which ionises / dissociates completely in water to form high concentration of hydroxide ions (OH ^– ).
• Example of strong alkali: Sodium hydroxide (NaOH) solution, potassium hydroxide (KOH) solution and barium hydroxide (Ba(OH)₂) solution.
• Example of the strong alkali reaction in water: NaOH(aq) –> Na⁺(aq) + OH^-(aq)

Weak Alkalis

• Weak alkali – an alkali which ionises / dissociates partially in water to form low concentration of hydroxide ions (OH ^– ).
• Example of weak alkali: ammonia (NH₃) solution.
• Example of the weak alkali reaction in water: NH₃(g) + H₂O(l) <—-> NH₄⁺(aq) + OH^- (aq)