Q.What are the limitations of Freundlich adsorption isotherm ?

Freundlich's adsorption isotherm is an empirical equation, x/m = k·p^(1/n), describing how much gas is adsorbed per gram of adsorbent at a given equilibrium pressure and fixed temperature.

The Freundlich adsorption isotherm relates the mass of gas adsorbed per unit mass of adsorbent (x/m) to the equilibrium pressure p (for adsorption of a gas) or equilibrium concentration C (for adsorption from solution), at a fixed temperature:

x/m = k · p^(1/n) (0 < 1/n < 1, i.e. n > 1)

where k and n are empirical constants depending on the adsorbent-adsorbate pair and temperature. Taking logarithms:

log(x/m) = log k + (1/n) log p

A plot of log(x/m) versus log p is a straight line with slope 1/n and intercept log k, which is how k and n are determined experimentally. The isotherm is only valid over a limited (moderate) pressure range — at very high pressure, x/m becomes independent of p (adsorption approaches saturation), which the simple power-law form doesn't capture.

OR (alternative part):

(i) Tyndall effect — when a strong beam of light is passed through a colloidal sol (in a dark room, viewed from the side), the path of the beam becomes visible as a bright, illuminated cone/path. This happens because colloidal particles, being comparable in size to the wavelength of light, scatter light in all directions.

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