When the voltage of the solution containing 0.1 M NaCl was measured by a pH meter, it was -0.45V at pH = 8, -0.57V at pH = 10, and -0.69V at pH = 13.0. Use the following equation to calculate the potentiometric

selectivity constant of the glass membrane used here.

Em=FRTlnaH++kH+,Na+potaNa+aH++kH+,Na+potaNa+=constant+FRTln(aH++kH+,Na+potaNa+)