what is the need to know amount of Fe2+ by titrating with KMnO4?
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Answer:
As with acid-base titrations, a redox titration (also called an oxidation-reduction titration) can accurately determine the concentration of an unknown analyte by measuring it against a standardized titrant. A common example is the redox titration of a standardized solution of potassium permanganate (KMnO4) against an analyte containing an unknown concentration of iron (II) ions (Fe2+). The balanced reaction in acidic solution is as follows:
[latex]MnO_4^-(aq)+5Fe^{2+}(aq)+8H^+(aq) \rightarrow 5Fe^{3+}(aq)+Mn^{2+}(aq)+4H_2O(l)[/latex]
In this case, the use of KMnO4 as a titrant is particularly useful, because it can act as its own indicator; this is due to the fact that the KMnO4 solution is bright purple, while the Fe2+ solution is colorless. It is therefore possible to see when the titration has reached its endpoint, because the solution will remain slightly purple from the unreacted KMnO4.
Permanganate Titration EndpointA redox titration using potassium permanganate as the titrant. Because of its bright purple color, KMnO4 serves as its own indicator. Note how the endpoint is reached when the solution remains just slightly purple.
Explanation:Experiment 8 –Redox TitrationsPotassium permanganate, KMnO4, is a strong oxidizing agent. Permanganate, MnO4-, is an intense dark purple color. Reduction of purple permanganate ion to the colorless Mn+2ion, the solution will turn from dark purple to a faint pink color at the equivalence point. No additional indicator is needed for this titration. The reduction of permanganate requires strong acidic conditions.In this experiment, permanganate will be reduced by oxalate, C2O42-in acidic conditions.Oxalate reacts very slowly at room temperature so the solutions are titrated hot to make the procedure practical. The unbalance redox reaction is shown below.MnO4-+ C2O42-→Mn2++ CO2(acidic solution)In part I of this experiment, a potassium permanganate solution will be standardized against a sample of potassium oxalate. Once the exact normality (eq/L) of the permanganate solution is determined, it can be used as a standard oxidizing solution. In part II of this experiment, the standard permanganate solution will be used to find the concentration of iron(II) in a ferrous solution(g/L).The unbalanced redox reaction is shown below.MnO4-+ Fe2+→Mn2++ Fe3+(acidic solution)Phosphoric acid will be used to ensure that the ferric product, Fe3+remains in its colorless form.