Determination of the HCl dissociation constant at a temperature of 350°C and 200 bars of pressure by the potentiometric method using a ceramic electrode

A technique has been developed for pH measurement in flow-through cells at temperatures from 175 to 350°C and pressures up to 350 bars in a nonisothermal cell consisting of a ZrO₂(Y₂O₃) ceramic electrode and a Ag/AgCl (2 M KCl, 25°C) flow-through reference electrode. This technique has been applied to determination of the HCl dissociation constant at 350°C and 200 bars; previously, the HCl dissociation has not been studied sufficiently reliably under these conditions. The obtained value pK _dis = 2.16 ± 0.03 was used to estimate the acidity of fluids from their chemical composition at the vent of high-temperature submarine hydrothermal solutions.