Strength of Acids and Alkalis

6.3

Strengths of Acids and Akalis

Degree of Dissociation

The strength of an acid or an alkali depends on the degree of dissociation in water (also known as the degree of ionisation).
Both acid and alkali can be divided into two, either strong or weak.
These all depend on the degree of dissociation in water.

Strong Acid

Definition

A strong acid is a chemical substance that can dissociate completely in water to form freely moving hydrogen ions, \(H^+\).

Example of Strong Acids

The diagram show example of strong acid such as hydrochloric acid, HCl, sulphuric acid H2SO4 and nitric acid HNO3

Weak Acid

Definition

A weak acid is a chemical substance that only dissociates partially in the water to form hydrogen ion, \(H^+\).

Example of Weak Acids

The diagram shows the example of weak acid such as ethanoic acid CH3COOH and carnonic acid H2CO3.

Strong Alkali

Definition

A strong alkali is a chemical substance that dissociates completely in water to produce hydroxide ion, \(OH^-\).

Example of Strong Alkalis

Sodium hydroxide, \(NaOH\)
Potassium hydroxide, \(KOH\)

Weak Alkali

Definition

A weak alkali is a chemical substance that dissociates partially in water to produce hydroxide ion, \(OH^-\).

Example of Weak Alkalis

Calcium hydroxide, \(Ca(OH)_2\)
Aqueous ammonium, \(NH_4OH\)