2. Using a nitrate-selective electrode, the content of NO3 ion in the solution was determined. A standard KNO3 solution was prepared by dissolving an accurately weighed portion of 0.4964 g in 100 ml of water. From this solution, a series of more diluted solutions with a concentration of C(KNO3) mol/l were prepared. For this, each previous solution was diluted 10 times with water in a volumetric flask. When measuring the electrode potentials of standard solutions, the following data were obtained:
C , mol/l n*10-2 n*10-3 n*10-4 n*10-5
E, mV 76.7 130.4 184.3 234.1
The test solution with a concentration of Cx was brought to the mark with water in a 100 ml volumetric flask and Ex, 166.8 mV, was measured. Calculate the exact concentration of standard KNO3 solutions, construct a calibration graph and determine the mass of nitrate ion in the test solution, g.

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