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 pK(i) = -34.97 + 2947/T + 6.086 ln(T) 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 pK2 = 4201.48 229 200/T - 661.21 ln(T) + 0.647 53T + 13 1498 200/T2 where T is in Kelvin. By using the temperature dependence of the dissociation constant, the isocoulombic reaction was studied. The plot of -log K(isoc) 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 K(isoc) to higher temperatures.