Four activated carbons, one of them commercially available Darco active carbon and the remaining three from a series of coconut charcoals steam activated to varying degrees, are used to study the adsorption of weak and non-electrolytes. Introduction of -Cl into the CH&OOH molecule increases adsorption onto activated carbon while -OH and -NH, have the opposite effect. Substitution in the benzene ring shows that adsorption from aqueous solutions is in the order -NH*, >-OH, >CO*, >(-OH + -COOH).
Effect of polarity of solvent on adsorption capacities is studied in H20, CHCl, and C6Hs. Substitution of -Cl into the CH,COOH molecule invariably increases the adsorption irrespective of the polarity of the solvent. On introducing a specific group in the benzene ring the adsorption is in the order: aniline 2 phenol > benzoic acid > salicylic acid in H20 medium but in CHCls and CbH, media aniline 2 phenol > salicylic acid > benzoic acid. However, on comparing the results of individual adsorbates in three media, generally the magnitude of adsorption is H20 > CGHb> CHC&. Adsorption of lower aliphatic acids (formic to caproic) from aqueous solutions increases regularly as one ascends the homologous series-a behaviour known as Traube's rule; however, of all the surface area available for Ns adsorption, only a fraction of it is available for adsorption of the aliphatic acids.