10/2016 11:55 PM A 12Al15 5/9/2016 08:55 PM Print Calculator Periodic Table Grad

Question

10/2016 11:55 PM A 12Al15 5/9/2016 08:55 PM Print Calculator Periodic Table Grade bo estion 9 of 9 apling leaming Mapdob Calibration of a glass electrode gave a reading of 125.3 mv with 0.05 m potassium hydrogen phthalate buffer standard (pH 4.015) and a reading of-74.3 mV with 0.008695 potassium dihydrogen phosphate, 0.0343 m disodium hydrogen phosphate buffer standard (pH 7.400), both measured at 300C (a) What is the observed slope (mVpH unit of the calibration curve? Number Slope observed mv pH What is the theoretical slope at 30°C? Number Slope mv/pH theoretical (cy what is 8, the electromotive open the hint panel below for the definition of electromotive efficiency to three significant figures?? efficiency. Number (d) What is the pH of an unknown that gives a reading of 36.0 mv with this electrode at 30c? Number pH Previous Give up & View Solution Check Answer Next Ex Hint privacy policy terms of use about us careers pai

Explanation / Answer

Slope S = dE/dpH

a) is (125.3-(-74.3mV))/(4.015pH-7.400pH) = -58.966

b) the theoretical slope is -2.303RT/nF ..... The known value at 298 K is - 0.058966 V.... The value at 303K (30 degrees) is...... -0.058966 V x 303K / 298K = -0.05996 V = -59.96 mV

c) (58.966 mV/pH)/(59.96 mV/pH) = 0.983

d) pHx = pH + (Ex-E)/S (pH and E, any known pair, look also at a., same equation) = 7.400 - (36.0 + 74.3)/ 58.966 = 7.454 - 1.870 = 5.584

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