For a certain glass electrode, the selectivity coefficient for Na+ relative to H+ is 1.0 x 10-12. The electrode is calibrated with NBS standard buffers 6.86 and 9.18, which produce no significant response to interfering ions. It is then used to measure the pH of 0.0100 M NaOH in 0.50 M NaCl at 25 oC.
What is the true pH of the solution and the observed pH? Use the Debye-Huckel equation to estimate acitivity coefficients.