Some solids are capable of adsorbing certain solutes from the solution. This property is made use of in adsorbing colouring matter from solutions of organic substances. Raw cane juice is decolourised by activated charcoal. Similarly, charcoal adsorbs oxalic and acetic acid dyes from their aqueous solutions.Freundlich adsorption isotherm is also applicable to solutions by replacing the pressure term by the concentration (C) of adsorbates in solutions. The relationship is modified as follows
x/m = kC(1/n)
Taking logarithm, it becomes
log x/m = logk + 1/n logC
A graph between log (x/m) and log C is a straight line for small ranges of
concentrations. |