A total of 2115 ml of K2Cr2O7 is required for the titration

A total of 21.15 ml of K2Cr2O7 is required for the titration of a 0.1414 gram sample of FeSO4, that is 88.88% pure. If the products are Cr +3 and Fe +2, write the correctly balanced equation.

b. You take a sample of iron ore, dry it, and then weigh it at 0.9757 grams. After dissolving it and reducing the natural Fe +3 to Fe +2, this sample was titrated with KMnO4. This sample required 10.55 ml of 0.03233 M KMnO4 to reach the equivalence point, where the permanganate was reduced to Mn +2. Calculate the % Fe in the original ore.

c. What are possible problems with this analysis?

Solution

Equation : 6FeSO4 + K2Cr2O7 + 7H2SO4 ===> 3Fe2(SO4)3 + Cr2(SO4)3 + K2SO4 + 7H2O

b.) 2KMnO4 + 10FeSO4 + 8H2SO4 → 5Fe2(SO4)3 + K2SO4 + 2MnSO4 + 8H2O

For this milliequivalents of KMnO4 reacted = 10.55*0.03233 * 5 = 1.70

Same should b milliequivalents of Fe2+ = 1.70

No. of millimoles of fe2+ = 1.70

Mass of Fe = 0.0952 grams..

Hence %age = 9.94%

c) The titration may nt b accurate as Fe2+ is easily oxidised by air.