The Debye-Huckel Approximation Results

The Debye-Hiickel approximation is strictly applicable only in the case of low potentials. Nevertheless, there are several reasons why the significance of Equation (37) should be fully appreciated  

It is simpler to understand than any of the modifications we consider subsequently. 

It is a limiting result to which all equations that are more general must, reduce in the limit of low potentials. 

The effects of electrolyte concentration and valence in this approximation are qualitatively consistent with the results of more elaborate calculations. 

One of the most important quantities to emerge from the Debye-Huckel approximation is the parameter k. This quantity appears throughout double-layer discussions and not merely at this level of approximation. Since the exponent kx in Equation (37) is dimensionless, k must have units of reciprocal length. This means that k has units of length. This last quantity is often (imprecisely) called the thickness of the double layer. All distances within the double layer are judged large or small relative to this length. Note that the exponent kx may be written x/k a form that emphasizes the notion that distances are measured relative to k in the double layer. 

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