Question

Mass of KyFe(C204)y. ZH20 : 4.60 g Mass of sample : 0.195 g Mass of FeCl3 used in preparation : 1.60 g Molarity of standard NaOH used : 0.100 V1, volume of standard NaOH required for first equivalence point : 6.000 mL V2, volume of standard NaOH required for second equivalence point : 16.40 mL The questions below are part of the final analysis, they are due at the beginning of the next lab, Wed Mar 25 12:00:00 pm 2020 (EDT). Calculate the mass of potassium in the sample : Submit Answer Incorrect. Tries 1/3 Previous Tries Calculate the percent of potassium in the sample : % Submit Answer Tries 0/3 Calculate the volume of standard NaOH that reacted with iron : mL Tries 0/3 Submit Answer Calculate the mass of iron in the sample : Submit Answer Tries 0/3 Calculate the percent of iron in the sample : Submit Answer % Fe Tries 0/3

Answer 1

• Calculate the mass of potassium in the sample :

  1st equivalence point corresponds to K+ ;

  mol K+ = moles of NaOH used in titration (from V1 ) = 0.100 mol/L * 6.00 ml/1000 ml/L = 0.00060 moles

  mass of K+ in sample =  0.00060 moles* 39.1 g/mol = 0.02346 g

  Calculate the percent of potassium in the sample :

  mass of K+ in sample / mass of sample *100

  0.02436 g / 0.195 g *100 = 12.03 %

  Calculate the volume of standard NaOH that reacted with iron :

  V2 -V1 = 16.40 ml - 6.00 ml = 10.40 mL

  Calculate the mass of iron in the sample :

  three moles of hydroxide ion are required to react with each mole of iron ion in the salt.

  moles of Fe = 1/3* moles of NaOH used in titration (form V2 - V1) = 0.100 mol/L * 10.4 ml/1000 ml/L /3 = 0.000347 moles

  mass of Fe in sample = (moles of Fe)(55.85 grams/mole) = 0.000347 moles*55.85 g/mol = 0.01936 g

  Calculate the percent of iron in the sample :

  mass of Fe in sample / mass of sample *100

  0.01936 g / 0.195 g *100 = 9.93 %