11. A sample weighing 0.5150 g was dissolved in 50.0 ml of distilled water. In the resulting solution, the electrode potential of the calcium-selective electrode relative to the silver-silver chloride reference electrode is 12.0 mV. In standard solutions containing known calcium ion contents, the potentials of the indicator electrode are measured. measured under identical conditions were:
c(Ca2), mol/l 1.0*10-1 1.0*10-2 1.0*10-3 1.0*10-4 1.010-5
E, mV 726.0 46.0 18.0 -8.0 -34.0
Calculate the mass fraction of calcium in the sample.

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