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

A spectrophotometric method has been used for the determinationof the dissociation constants of some weak indicator bases invarious ethyl cellosolve (ECS)-water solvent mixtures at 25ºC. Theindicators used are p-nitro, o-nitro and m-nitroaniline. The dissociationconstants are found to decrease with increase of ECS for allinvestigated indicators which indicates that the basicity of the mediumis increased by the addition of solvent. The acidity function, Hº, ofHCl in water-ECS mixtures is also determined and is found toincrease with concentration increase of organic solvent for a fixedacid concentration. This is explained owing to the salting-in effectwhich depends on the used solvent type.