Final answer:
The Freundlich isotherm has a logarithmic relationship. It is used to describe how the adsorption capacity is related to the concentration of an adsorbate in solution, which plots as a non-linear graph unless transformed to a logarithmic scale.
Step-by-step explanation:
The relationship described by the Freundlich isotherm is logarithmic. The Freundlich isotherm represents the adsorption of substances onto surfaces and indicates that the binding sites are not equivalent and/or the surface concentrations are not homogenous. The adsorption capacity is related to the concentration of the adsorbate in the solution by a logarithmic relationship, which can be represented by the Freundlich equation:
C = kads1/n
where C is the amount adsorbed, k is the Freundlich constant, ads is the adsorbate concentration, and 1/n is the heterogeneity factor. In practice, this leads to a plot that is not linear unless the data are transformed into a logarithmic scale, at which point the Freundlich isotherm can be plotted linearly. This is useful in analyzing the adsorption characteristics of various materials.