Calibration of a glass electrode gave a reading of 129.7 mV with a saturated potassium hydrogen tartrate buffer standard (pH = 3.557), and a reading of -98.7 mV with a 0.008695 m potassium dihydrogen phosphate,0.0343 m disodium hydrogen phosphate buffer standard (pH = 7.400), both measured at 30 °C.What is the observed slope (mV/pH unit) of the calibration curve?slopeobserved =mV/pHWhat is the theoretical slope at 30 °C?slope heoreticalmV/pHWhat is the pH of an unknown that gives a reading of 18.5 mV with this electrode at 30 °C?pH =

The response of a glass electrode is given by the equation: E=constant-β(0.05916)(pH) (A)At pH = 3.557, using equation (A): 129.7 (mV)=constant-β(0.05916)(3.557)129.7-constant(0.05916)(3.557)=-β (B) At pH = 7.400, using equation (A): -98.7 (mV)=constant-β(0.05916)(7.400) (C)Substituting (B) into (C):-98.7 (mV)=constant+(129.7-constant)(0.05916)(3.557)(0.05916)(7.400)-98.7=constant+(129.7-constant)(2.080)-98.7=constant+269.776-2.080 constant-368.476=-1.080 constantconstant=341.18Observed readings: E pH 129.7 3.557 -98.7 7.4 Equation of line obtained from excel plot: y=-59.433x+341.1 Thus, Slopedobserved=-59.433 mV/pHUsing equation (C), and the value obtained for constant: -98.7 (mV)=341.18 (mV)-β(0.05916)(7.400)Slope of the plot of E versus pH as per equation A is -β(0.05916)Thus, solving for -β(0.05916),-β(0.05916)=Slopetheoretical=-59.443 mV/pHUsing equation (A) for the unknown, 18.5 (mV)=341.18-β(0.05916)(pH)18.5 (mV)=341.18-(59.443)(pH)pH=5.43