CATEGORIZATION OF WEAK AND STRONG ELECTROLYTES

 Weak and Strong Electrolytes

Weak electrolytes are compounds that are only partially or slightly ionized in aqueous solutions.

Some substances, for example, ethanoic acid solution ionize partially.

CH3COOH(aq)    ------->   CH3COO-(aq) + H+(aq)

Most of the electrolytes exist in solution in the form of unionized molecules. For example, in ordinary dilute (2M) ethanoic acid, out of every 1000 molecules present, only 4 are ionized and 996 are unionized. 

A solution of ammonia water is also a weak electrolyte, containing a relatively small proportion of ammonium and hydroxyl ions.

NH4OH(aq)  ------> NH4+(aq) + OH-(aq)

Most of the organic acids are weak electrolytes, e.g. tartaric, citric and carbonic acids.

However, there is no sharp dividing line between weak and strong electrolytes.Water is also a weak electrolyte. It ionizes only slightly.

H2O(l)  ------>   H+(aq) + OH-(aq)

Study shows that for every molecule of water ionized, there are 6 million molecules of water not ionized. Strong electrolytes are compounds that are completely ionized in aqueous solutions. When sodium chloride is dissolved in adequate water it ionizes completely into Na⁺and Cl^- ions. There are no NaCl solid particles left unionized. All strong electrolytes (salts, the mineral acids and caustic alkalis) ionize completely in solutions.