Effect of anion basicity in influencing the acidity function of concentrated aqueous solutions of oxyacids
- 1 January 1979
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 75, 1606-1612
- https://doi.org/10.1039/f19797501606
Abstract
The measurement of Hammett acidity of anhydrous acids and their concentrated aqueous solutions by amine indicators is viewed in terms of the transference of a proton to the —NH2 group from a solvating cluster provided by the medium. It is argued that a measure of the difficulty with which the proton can be transferred should be given by the optical (Lewis) basicity of the deprotonated solvating cluster. Optical basicities for clusters of various sizes are calculated for the systems H3PO4+ H2O, H2SO4+ H2O and HClO4+ H2O, and the values are found to increase with increasing water content of the solvating cluster in line with the decreasing acidity of the medium. When they are plotted against the H0 values of the corresponding acid solutions, straight line relationships are observed which are especially good when based upon two molecule and three molecule solvating clusters. These relationships indicate the dependence of H0 not only upon the water content but also the decreasing basicity in going from phosphate to sulphate to perchlorate. Changes in H0 with change of indicator and the prediction of H0, e.g. for oleum and orthosilicic acid, are also discussed.Keywords
This publication has 0 references indexed in Scilit: