Calibration of a glass electrode gave a reading of 136.9 mV with 0.05 m potassiu

Question

Calibration of a glass electrode gave a reading of 136.9 mV with 0.05 m potassium hydrogen phthalate buffer standard (pH = 4.015) and a reading of -63.7 mV with 0.008695 potassium dihydrogen phosphate, 0.0343 m disodium hydrogen phosphate buffer standard (pH = 7.400), both measured at 30degree C. (a) What is the observed slope (mV/pH unit) of the calibration curve? Slope_observed = (b) What is the theoretical slope at 30degree C? Slope_theoretical = (c) What is beta, the electromotive efficiency to three significant figures ?? Open the hint panel below for the definition of electromotive efficiency. beta = (d) What is the pH of an unknown that gives a reading of 45.6 mV with this electrode at 30degree C? pH =

Explanation / Answer

a) Observed slope = (Reading 2 - Reading 1) / (pH 2 - pH 1)

= (-63.7 - 136.9) / (7.4 - 4.015)

= -59.26 mV/pH

b) As per the data given Observed slope = Theoritical Slope = -59.26 mV/pH

c) Insufficient data

d) -59.26 = (-63.7 - 45.6) / (7.4 - x)

Therefore, pH of an unknown (x) = 5.56

  

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