141. Solving a chemistry problem

141. Solving a chemistry problem

In standard solutions of potassium salt with a concentration of CK, the electrode potentials of the potassium selective electrode relative to the silver chloride electrode were measured and the following data were obtained:
CK, mol / L 1.0 * 10-1 1.0 * 10-2 1.0 * 10-3 1.0 * 10-4
E, mV 100 46.0 -7.00 -60.0
Based on these data, a calibration graph was constructed in the coordinates E - pK. A sample of a sample weighing 0.2000 g containing potassium was dissolved in water and the volume was adjusted to V (ml). Then measured the electrode potential of the potassium selective electrode (EX) in the resulting solution:
Option 1 2 3 4
V, ml 100.0 250.0 500.0 1000
Ex, mV 60.0 34.0 10 -30
Calculate the mass fraction (%) of potassium in the sample.

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