Study of the Dissociation Constants of Some Weak Indicator Bases in Ethyl Cellosolve - Water Solvent Mixtures

Abstract

Abstract.A spectrophotometric method has been used for the determination of the dissociation constants of some weak indicator bases in various ethyl cellosolve (ECS)-water solvent mixtures at 25ºC. The indicators used are p-nitro, o-nitro and m-nitroaniline. The dissociation constants are found to decrease with increase of ECS for all investigated indicators which indicates that the basicity of the medium is increased by the addition of solvent. The acidity function, H º , of HCl in water-ECS mixtures is also determined and is found to increase with concentration increase of organic solvent for a fixed acid concentration. This is explained owing to the salting-in effect which depends on the used solvent type.