A sample is analyzed to determine its iron content Fe2+ via a redox titration with potassium...

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Chemistry

A sample is analyzed to determine its iron content Fe2+ via aredox titration with potassium chromate as the titrant. In thetitration Fe2+ is oxidized to Fe3+ and CrO4 2- is reduced to Cr 3+.What is the percent by mass of iron in the sample if 0.9087g of thesample required 45.68mL of a 0.04322 M K2CrO4 solution to reach theendpoint?

I worked out the balanced equation to be:

8H+ + 3Fe2+ + CrO4 2- = 3Fe3+ + Cr3+ + 4H2O

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4.1 Ratings (790 Votes)

8H+ + 3Fe2+ + CrO4 2- = 3Fe3+ + Cr3+ + 4H2O

no of moles of K2CrO4 = molarity* volume in L

                                         = 0.04322*0.04568   = 0.00197 moles

K2CrO4 ---------> 2K+ + CrO42-

0.00197moles              0.00197moles

from balanced equation

1 mole of CrO42- react with 3 moles Fe2+

0.00197 moles CrO42- react with = 3*0.00197/1 = 0.00591moles of Fe+2

mass of Fe   = no of moles* gram atomic mass

                    = 0.00591*56 = 0.33096g of Fe

mass percentage of Fe = 0.33096*100/0.9087   = 36.42%


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