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 µmol dm 3nH2SO4 solution were estimated by use of an ionicnliquid salt bridge (ILSB), made of tributyl(2-meth-noxyethyl)phosphonium bis(pentafluoroethanesulfo-nnyl)amide (TBMOEPC2C2N), sandwiched by twonhydrogen electrodes. The experimental pH valuesn(pH log aH, where aH is the activity of hydrogennions) were in good agreement, within 0.01 pH unit,nwith those calculated using the Pitzer model. Thendifference between the experimental and theoreticalnpH values at 50 µmol dm 3 H2SO4 solution wasnmuch smaller than that obtained by use of a glassnelectrode in combination with a reference electrodenwith a concentrated KCl salt bridge. The sourcenof the small deviation can be explained by the resi-ndual diffusion potential due to the dissolution ofnTBMOEPC2C2N in the H2SO4 solution (W) and thenresultant increase in the ionic strength of W. The usenof a reference electrode equipped with an ILSBnopens the way to accurately estimate the pH in dilutenaqueous solutions, for which we have not had effec-ntive means.