Spectroscopic measurement of the acid dissociation constant of 2-naphthol and the second dissociation constant of carbonic acid at elevated temperatures

2-Naphthol can be used to measure the pH of aqueous solutions if the acid dissociation constant for 2-naphthol is known at a given temperature. The temperature dependence of the acid dissociation constant for 2-naphthol was spectroscopically determined in borate buffer solutions under vapor-saturated pressure up to 200°C. The result was where T is in Kelvin. The pH of carbonate buffer solutions was measured by obtaining the UV–visible spectra of 2-naphthol and utilized to determine the second dissociation constant of carbonic acid up to 175°C under vapor-saturated pressure. The result was where T is in Kelvin. By using the temperature dependence of the dissociation constant, the isocoulombic reaction was studied. The plot of -log Kisoc against 1/T was approximately linear in the temperature range studied. The linearity can be used to predict the dissociation constant by the extrapolation of -log Kisoc to higher temperatures.