05 Chemical Bonds
06 Acids, Bases and Salts
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6.3.1 Strength of Acids and Alkalis

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 the 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 a small portion of the molecules are ionised to release hydroxide ions.
  4. The table below shows some example of strong/weak alkalis.
Alkali
Strong
Weak
NaOH
KOH
LiOH
NH3