Determination of the Activity of Hydrogen Ions in Dilute Sulfuric Acids by Use of an Ionic Liquid Salt Bridge Sandwiched by Two Hydrogen Electrodes

摘要

The activities of hydrogen ions in 20-200 (mu)mol dm~(-3) H_(2)SO_(4) solution were estimated by use of an ionic liquid salt bridge (ILSB), made of tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide (TBMOEPC_(2)C_(2)N), sandwiched by two hydrogen electrodes. The experimental pH values (pH velence -log a_(H), where a_(H) is the activity of hydrogen ions) were in good agreement, within 0.01 pH unit, with those calculated using the Pitzer model. The difference between the experimental and theoretical pH values at 50 (mu)mol dm~(-3) H_(2)SO_(4) solution was much smaller than that obtained by use of a glass electrode in combination with a reference electrode with a concentrated KCl salt bridge. The source of the small deviation can be explained by the residual diffusion potential due to the dissolution of TBMOEPC_(2)C_(2)N in the H_(2)SO_(4) solution (W) and the resultant increase in the ionic strength of W. The use of a reference electrode equipped with an ILSB opens the way to accurately estimate the pH in dilute aqueous solutions, for which we have not had effective means.