11.2 Electrolytes

Lets have a look at compounds we call electrolytes and see what makes them an excellent conductor of electricity.

What makes the flow of electricity possible in solution?  For the flow of electricity, we need to have a charged particle that can run from one place to another and carry the charge.  In solid wires in our homes, electrons are responsible for moving and carrying the charge that allows the flow of electricity through wires. When ionic compounds, acids or bases are allowed to mix with water, they dissociate or ionize in the solution and produce ions. These free-floating ions are responsible for the flow of electricity in the solution. These compounds which allow the flow of electricity in solution are called Electrolytes.

Potassium chloride, an ionic compound dissociate to produce Potassium and chloride ions. 

KCl (s)           K⁺ (aq) + Cl^– (aq) Eq. 11.2

Fig. 11.2 Potassium chloride dissociating to produce ions in solution.

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Some covalent compounds, also ionize in solution and produce ions, and will act as an electrolyte.  Equations below show the ionization of acetic acid (HC₂H₃O₂) and ammonia (NH₃) in water.

 HC₂H₃O₂ + H₂O              C₂H₃O₂ ^– + H₃O⁺    Eq. 11.3

NH₃ + H₂O              OH^– + NH₄⁺  Eq. 11.4

In the example above, acetic acid (HC₂H₃O₂), a weak acid, produced few C₂H₃O₂ ^– and H₃O⁺  ions in the solution hence will act as a weak electrolyte.  Similarly, NH_3, a weak base, produced few OH^– and NH₄⁺ ions in solution and will be a weak electrolyte.

Other covalent compounds dissolve in water but do not ionize.  Since no ions are present in these solutions, they do not allow the flow of electricity.  We call these compounds nonelectrolytes.  Ethanol is an excellent example of non electrolyte.

C₂H₅OH(l)                                C₂H₅OH (aq) Eq. 11.5

Fig. 11.3

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The picture above is an illustration of the dissolution of three different compounds in water. The leftmost picture shows dissolution of ethanol, a covalent compound, in water. It did not produce any ions in the solution.  Therefore it is a nonelectrolyte and the bulb did not light up in this solution. In the middle picture, KCl, an ionic compound and a strong electrolyte produced lot of ions, hence bulb lit up very brightly. The picture on the right shows acetic acid, which produces few ions in solution.  Therefore it is a weak electrolyte and and as a result, the bulb lit up but it looks very dim.

Watch this video for a further understanding of electrolytes.