Potassium dichromate is used to titrate a sample containing an unknown percent o

Question

Potassium dichromate is used to titrate a sample containing an unknown percent of iron. The sample is dissolved in sulfuric acid and phosphoric acid mixture to reduce all the iron to Fe+2 ions. The solution is then titrated with 0.01625 mol.dm-3 of a K2Cr2O7, producing Fe+3 and Cr+3 ions in acidic solution. The titration requires 32.26ml of potassium dichromate for 1.2765 grams of sample.   
Calculate the mole of Fe+2 Potassium dichromate is used to titrate a sample containing an unknown percent of iron. The sample is dissolved in sulfuric acid and phosphoric acid mixture to reduce all the iron to Fe+2 ions. The solution is then titrated with 0.01625 mol.dm-3 of a K2Cr2O7, producing Fe+3 and Cr+3 ions in acidic solution. The titration requires 32.26ml of potassium dichromate for 1.2765 grams of sample.   
Calculate the mole of Fe+2 Potassium dichromate is used to titrate a sample containing an unknown percent of iron. The sample is dissolved in sulfuric acid and phosphoric acid mixture to reduce all the iron to Fe+2 ions. The solution is then titrated with 0.01625 mol.dm-3 of a K2Cr2O7, producing Fe+3 and Cr+3 ions in acidic solution. The titration requires 32.26ml of potassium dichromate for 1.2765 grams of sample.   
Calculate the mole of Fe+2

Explanation / Answer

the concentration of Fe+2 is calcualted by titrating it against K2Cr2O7

The volume of K2Cr2O7 required = 32.26mL

the concentration of 0.01625 mol / L

so moles of K2Cr2O7 = molarity X volume = 0.01625 X 32.26 = 0.524 millimoles

The balanced equation is

10 FeSO4 + K2Cr2O7 + 7 H2SO4 5 Fe2(SO4)3 + K2SO4 + Cr2(SO4) + 7 H2O

So each mole of K2Cr2O7 will oxidized 10 moles of Fe+2

Moles of Fe+2 present = moles of K2Cr2O7 present / 5 = 0.524 / 5 = 0.1048 millimoles

= 0.1048 X 10^-3 moles of Fe+2

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