SPM Chemistry

Strength of Acids/Alkalis

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Strong Acids and Weak Acids

  1. Acids are chemical substances that ionize/dissociate in the presence of water to produce hydrogen ions (or hydroxonium ions).
  2. Acids can be classified into 2 categories:
    1. Strong acids
    2. Weak acids
  3. The strength of an acid depends on the degree of ionization/dissociation of the acid.

Strong Acids

Strong acids are acids that ionise completely to form hydrogen ions in water.
Examples:
Sulphuric acid
Hydrochloric acid
Nitric acid
Weak Acids
Weak acids are acids that partly ionise to form hydrogen ions in water.
Examples:
Ethanoic acid
Phosphoric acid
Citric acid

Strength of Alkali

  1. Similar to strength of acids, the strength of an alkali is defined by its ability to ionise and release hydroxide ions (OH–) in the solution.
  2. In a solution of strong alkali, all the alkali molecules are ionised in the water to produce hydroxide  ions.
  3. In a solution of weak alkali, only small portion of the molecules are ionised to release hydroxide ions.
  4. Table below shows some example of strong/weak alkalis.

Alkali
Strong
Weak
NaOH
KOH
LiOH		 NH3