Ferrous sulfate, FeSO4 was titrated by potassium permanganate, KMnO4 in my chemi

Question

Ferrous sulfate, FeSO4 was titrated by potassium permanganate, KMnO4 in my chemistry lab experiment with the following equation:

5Fe + 8H2SO4 + 2KMnO4 --> 5FeSO4 + 2MnSO4 + K2SO4 + 8H2O

subsequently, mass of iron Fe2+ was found. A question in the lab sheet was asked if ferrous fumarate, FeC2H2O4 instead of FeSO4 were titrated with KMnO4 in the same experiment using the same titrating method, what problem would be encountered? I learned that ferrous fumarate, FeC2H2O4 can react with potassium permanganate, KMnO4 as shown in the following chemical formula:

2KMnO4 + 3FeC2H2O4 --> K2CO3 + 2MnO2 + 3H2O + 5CO2 + 3Fe

I know the molarity of KMnO4 is 0.007626 mol / liter as given in the lab. Why the titration cannot be applied same as Ferrous sulfate, FeSO4? If not, would the answer be higher or lower than actual mass of ferrous fumarate, FeC2H2O4? Please explain.

Explanation / Answer

The oxidation of oxalate by permanganate to yield carbon dioxide is a well-studied reaction . Under the conditions stated in the question, the total reaction would be

2KMnO4 + 3FeC2H2O4 --> K2CO3 + 2MnO2 + 3H2O + 5CO2 + 3Fe

The balanced equation can be obtained using the usual methods for balancing redox reactions, such as the ion-electron method and the half-reaction method.

The titration cannot be applied the same as Ferrous sulfate, FeSO4, as there is no notable physical change involved except for fumes of CO2 observed. For titration calculations it is very important for an observable change to take place, otherwise, the end point of the reaction cannot be known.

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