38. Solving a chemistry problem

772. Determination of substance A in the analyzed solution was carried out by direct potentiometry. First, reference solutions were prepared with various precisely known concentrations C(A) of the analyte, after which the reference solutions were introduced one by one into an electrochemical cell, including the corresponding ion-selective indicator electrode and a silver chloride reference electrode, and the electromotive force E of the circuit was measured for each reference solution . Then, under the same conditions, the electromotive force of the circuit with the analyzed solution was measured.
Based on the data below, construct a calibration graph * in the coordinates E - pA, where
рА = –lgC(A), and determine the molar concentration of substance A in the analyzed solution
Option Substance A Electromotive force E of the circuit, mV
Reference solutions with concentration С(А), mol/l Analyzed solution
0.00001 0.0001 0.001 0.01 0.1
in Cd2 –168 –144 –120 –97 –72 –108
*To build a graph when applying scale scales to coordinate axes, it is recommended to choose for each scale such a scale at which one small cell on millimeter paper would correspond to the abscissa axis pA = 0.05, and along the ordinate axis - E = 2 mV.