Evaluation of o-and p-aminophenol polymers as indicators for acidity function spectrophotomerically

ABSTRACT

The Ultraviolet absorption spectra of o-aminophenol and p-aminophenol redox product polymers as indicators in different acidic solutions are investigated. They support the idea that the indicator reacts with H+ ions existing in solutions by proton transfer. The values of the indicator ratios I and thermodynamic ionization constant pkBH+ are calculated. Also, the evaluation of the acidity function H degree of the different solutions are given. Values of Hammett's acidity function of different concentrations for acetic acid, hydrochloric, nitric and sulphuric acids in aqueous and ethanolic solutions are computed from the spectrophotometrically measured indicator ratios of o-AP and p-AP polymers. The order of acid strength of the investigated acids in these media is discussed. In case of o-polymer the rate of decrease of log I-log CH with CH is appreciably decreased with the increase of CH in the order of protonation of p-polymer is more pronounced by H2SO4. It was found that, generally, the o-AP polymer indicator is more sensitive than the p-AP polymer in measurements of the acidity function H degree of different solutions