Iron Analysis


Objectives
To quantitatively analyze an iron containing compound by a redox chemical reaction.

Discussion
You will be given one of the following problems to solve: determine the molecular formula of hydrated ferrous salt, determine the percentage of iron in a sample, determination of the purity of a iron compound, or determine the concentration of ferrous ion (Fe2+) in a solution. In all cases the main redox reaction will center around the following unbalanced reaction: Fe2+ + MnO41- + H1+ ------> Mn2+ + Fe3+ + H2O

After sample preparation you will titrate the Fe2+ ion solution with a KMnO4 solution until the color of the purple MnO41- persists. The unbalanced half reactions involved are:
Fe2+ ----> Fe3+ + 1e-
MnO41- + 5e- ----> Mn2+ + H2O

The class will be responsible for mixing up all solutions. Since you will not know the concentration of iron in your sample you will have to make some assumptions in order to mix up the potassium permanganate solution. The assumptions made will depend on the type of problem given to you by your instructor.

Procedure
Have your procedure approved by your instructor prior to starting the experiment.

Questions
Questions will be given to you by your instructor depending on the analysis performed. Your lab report should contain all calculations summarized in a neat table.


Teacher Notes

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I feel that students rely too heavily on cook-book type experiments. Therefore, I do several labs with my Chem II students where they have to devise there own procedure in an attempt to get them to do some thinking on their own. The simplest use of this laboratory investigation is determining the normality of a ferrous solution. Determining either the purity of a ferrous compound or the molecular formula of a ferrous hydrate is more challenging.

One year I told students that they were working with FeSO4(H20)5 that was several years old. Their task was to determine the percentage of water lost from the sample due to dehydration. If you come up with other practical applications for the ferrous ion titration, please let me know.

Suggestion from John A. Raasch
Perhaps students could do the following: (1) set up a simple aquarium with a fast-growing plants, (2) fertilize plants with a known concentration of iron (should probably check water for existing iron, especially if it is well water), (3) measure iron concentration every few days to find out how rapidly it declines and when fertilizer should be applied again (assuming the goal was to enhance growth). This could be tied in with plant  growth, agriculture, timing application of fertilizer to reduce ground-water contamination. Perhaps this could be done with potted plants by checking iron in  soil. The idea needs a lot more work. If you would like me to refine it, just let  me know.


 
Questions? Comments??