The pH meter as a hydrogen-ion concentration probe

Abstract

Results obtained with three commercial pH meters, by measuring the e.m.f. of cells consisting of glass electrodes coupled with either calomel or silver chloride reference electrodes, are compared with the hydrogen-ion concentrations in solutions with three different background electrolytes at five or six different levels of salt concentration. The hydrogen-ion functions measured in this way can be empirically converted into concentrations for use in calculating equilibrium constants. When thermodynamic equilibrium constants cannot be calculated from such measurements it is preferable to report concentration quotients. Concordance is demonstrated among values of the second-stage ionisation constant for sulphosalicylic acid, measured in different ionic media and with different reference electrodes, when all values are converted into concentration quotients.