Strength of Acids and Bases

Learning Objectives

  • The Brønsted-Lowry theory of acids and bases including polyprotic acids and amphiprotic species, and writing of balanced ionic equations for their reactions with water including states

  • The distinction between strong and weak acids and bases, and between concentrated and dilute acids and bases, including common examples

Summary Notes

Properties of Acids and Bases

Acids and bases both have distinctive properties.

A Brønsted-Lowry acid is known as a proton donor while a Brønsted-Lowry base is known as a proton acceptor.

This means that an acid will lose a H⁺ ion while a base will gain a H⁺ ion.

Strength of Acids and Bases

The strength of acids and bases can be determined by the ability for the substance to gain or accept protons.

A stronger acid or base is a substance that readily donates or accepts a proton. They also completely ionise.

  • HCl (l) + H₂O (l) → H₃O⁺ (aq) + Cl⁻ (aq)

  • Mg(OH)₂ (s) → Mg⁺² (aq) + 2OH⁻ (aq)

A weak acid or base is a substance that does not donate or accept protons readily. They only partially ionise.

  • CH₃COOH (l) + H₂O (l) ⇌ H₃O⁺ (aq) + CH₃COO⁻ (aq)

  • NH₃ (g) + H₂O (l) ⇌ NH₄⁺ (aq) + OH⁻ (aq)

Take note of the arrow used to represent partial ionisation. This means the reactions are reversible.

Concentration vs Strength

Concentration refers to how much of a substance is present in a system.

A solution can be concentrated or dilute depending on the amount of acid or base that has been diluted in water.

Videos to help your understanding

Strengths of Acids and Bases

Conjugate Acid and Bases

Practice Material

Conjugate Acid and Base Quiz