Evidence for non-ideality in electrolyte solutions

The Debye-Htickel theory deals with departures from ideality in electrolyte solutions. The main experimental evidence for this non-ideality is that  

These departures from ideality become less as the concentration decreases, and behaviour approaches ideality. They are taken care of thermodynamically as the non-ideal part of the free energy, often called the excess free energy , G . This can alternatively be expressed in terms of activity coefficients. 

Departures from ideality in electrolyte solutions have been shown (see Chapter 1) to be mainly due to  

Although this is the major factor other smaller contributions must be considered  

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