Mass of KxFe(C2O4)y · zH2O : 3.58 g
Mass of sample : 0.161 g
Mass of FeCl3 used in preparation : 1.60 g
Molarity of standard NaOH used : 0.0990
V1, volume of standard NaOH required for first equivalence point : 8.700 mL
V2, volume of standard NaOH required for second equivalence point : 17.70 mL

Calculate the mass of potassium in the sample

thanks so much

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