6.3	Strength of Acids and Alkalis

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

• A strong acid is a chemical substance that can dissociate completely in water to form freely moving hydrogen ions, \(H^+\). 
• Example of strong acids are:
  • Hydrochloric acid, \(HCl\)
  • Sulphuric acid, \(H_2SO_4\)
  • Nitric acid, \(HNO_3\)

 

Weak Acid

• A weak acid is a chemical substance that only dissociates partially in the water to form hydrogen ion. 
• Example of weak acids are:
  • Ethanoic acid, \(CH_3COOH\)
  • Carbonic acid, \(H_2CO_3\)

 

Strong Alkali

• A strong alkali is a chemical substance that dissociates completely in water to produce hydroxide ion, \(OH^-\). 
• Example of strong alkalis are:
  • Sodium hydroxide, \(NaOH\)
  • Potassium hydroxide, \(KOH\)

 

Weak Alkali

• A weak alkali is a chemical substance that dissociates partially in water to produce hydroxide ion, \(OH^-\). 
• Example of weak alkalis are:
  • Calcium hydroxide, \(Ca(OH)_2\)
  • Aqueous ammonium, \(NH_4OH\)