Calibration of a glass electrode gave a reading of 145.7 mV with 0.05 m potassium hydrogen phthalate buffer standard (pH = 4.015) and a reading of -54.0 mV with 0.08 m HEPES, 0.08 m NaHEPES, 0.08 m NaCl buffer standard (pH = 7.454), both measured at 30°C.
a) What is the observed slope (mV/pH unit) of the calibration curve?
b) What is the theoretical slope at 30°C?
c) What is ?, the electromotive efficiency to three significant figures? Open the hint panel below for the definition of electromotive efficiency.
d) What is the pH of an unknown that gives a reading of 47.5 mV with this electrode at 30°C?