Calibration of the glass electrode in pyridine

For the purpose of calibrating the glass electrode in py r i dine, the conductometric and the potentiometric measurements were made for the mixtures of the nitrophenols with the ir tetrabutylammonium salts. A new equation have been derived for calculating the electrol y tic conductivity of ion from the ionic concentrations. This equation was applied to t he experimental values of conductivity in order to obtain more reliable equilibrium constants in these system. It was necessary to take into account the ion pair formation between the homo c onjugate ion and tetrabutylammonium ion, especially in the case of the very weak a c ids such as mono-nitrophenols. The equilibrium constants represented by eq. (3), (4), (6) and ( 18)were determined respectively as given in Table 4. A saturated solution of tetramethylammonium chloride in pyridine was used as the electrolyte solution of the reference electrode for the potentiometric measurement. The r elations between the potential of the glass electrode, E, and log(ca/c8), where ca and c8 den ote the analytical concentrations of nitrophenols and their tetrabutylammonium salts, respecti v ely, are summarized in Fig.2. The hydrogen ion activity, a(H+), in the mixtures of the nitrophenols and their salts was calculated by using ca, c8 and the equilibrium constants obtaine d above. The calibration curve in pyridine which pa(H+) values are plotted vs. po tential, are shown in Fig.3. A good linear relation was obtained in the mixtures of the nitr ophenols and their salts. The equation-for the calculation of pa(H+) from glass electrod e measurements was pa(H+)=(352-E)/64, where E was given in millivolts.