An antibiotic compound (symbolized AB-O^+) can be reduced reversibly to a pure s
ID: 1069998 • Letter: A
Question
An antibiotic compound (symbolized AB-O^+) can be reduced reversibly to a pure solid form AB(s) at an inert solid electrode (for instance platinum) according to the half reaction: AB-O^+ + 2H^+ + 3e^- doubleheadarrow AB(s) + H_2O E degree = 0.107 V a. As analytical chemist in a pharmaceutical company producing the antibiotic, describe how you would practically develop an analytical method based on potentiometry to monitor AB-O^+ concentration in various batches. Comment on the sensitivity of this method based on the mathematical equation that you derive. b. An unknown concentration of the antibiotic AB-O^+ gave an electrode potential E = -0.288 V versus SHE at pH = 7. Calculate the unknown concentration of AB-O^+. c. How can the same electrode be used to monitor the pH? Derive the equation relating potential measured to pH. How docs the sensitivity of this pH determination compare with the sensitivity of the electrode when it is used to monitor AB-O^+? d. Calculate both the formal potential (E degree) and the measured potential (E of question b above) versus the Ag/AgCl reference electrode (of course using the values given vs. SHE)Explanation / Answer
Ecell = E' cell + 0.059/n log [M^n+] at room Temprature at 298 Kelvin
E cell = -.288 V
E'cell = .107 V
n = 1
-.288 = .107 +.059/1 log [AB-O+]^1
-.395 = .059 log [AB-O+]
-6.67 = log[AB-O+]
.0012 M =AB-O+