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Strong And Weak Electrolytes

A solute when dissolved in water may produce three different types of solution depending upon whether it is a good, poor or bad conductor of electricity. The conduction in the solution is due to the movement of ions. Hence a good conducting solution contains a larger number of ions, a poor one contains lesser number of ions and the bad one will not contain any ions. The ions in the solution are produced by dissolving the solute (also known as electrolyte) in water. Based on the conducting ability, an electrolyte may be classified into three categories as described below.


Conducting Ability


Strong electrolyte


NaCl, KCl, KBr, NH4Cl, HCl, H2SO4, NaOH

Weak electrolyte


PbCl2, HgCl2, H2CO3, CH3COOH

Non - electrolyte


CH3OH, CHCl3, CCl4

The classification of compounds in terms of strong and weak electrolytes is based on their behaviour in a particular solvent, namely, water. However, such a classification suffers from a great disadvantage in the sense that a particular electrolyte, though weak in water, might behave as a strong one when dissolved in some other solvent or vice versa. For example, sodium chloride behaves as a strong electrolyte and acetic acid as a weak electrolyte when dissolved in water. However, when acetic acid and sodium chloride are dissolved in ammonia, their conducting abilities are comparable, indicating a strong electrolyte behaviour for acetic acid.

Thus, the above classification depends upon the solvent used. Another classification that is largely based on the characteristics of the solute and not on that of the solvent is to label them as the true electrolyte and the potential electrolyte. 

The essential characteristic of a true electrolyte is that even in the pure liquid state it is an ionic conductor. In dissolution process, all that a polar solvent does is to use ion-dipole forces to disengage ions from their lattice sites, solvate them and disperse them into the solution. Examples are NaCl, KCl, etc. The potential electrolyte, however, does not conduct in the pure liquid state, though it provides a conducting solution on dissolution in an ionic solvent. Examples are hydrochloric acid, acetic acid, etc.

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