AP CHemistry: Determination of Iron by reaction with Permanganate- A redox titration.
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Potassium permanganate, KMnO4, is widely used as an oxidizing agent in volumetric analysis. In acid solution, MnO4- ion undergoes reduction to Mn2+ as shown in the following equation:
8 H+ (aq) + MnO¬4- (aq) + 5 e-  Mn2+ (aq) + 4 H2O
Since the MnO4- ion is violet and the Mn2+ ion is nearly colorless, the end point in titration using KMnO3 as the tyrant can be taken as the first permanent pink color that appears in the solution.
KMnO4 will be employed in this experiment to determine the percentage of iron in an unknown containing iron (II) ammonium sulfate, Fe (NH4)2(SO)2 * 6 H2O. The titration, which involves the oxidation of Fe2+ ion to Fe3+ by permanganate ion, is carried out in sulfuric acid solution to prevent the air oxidation of Fe2+. The end point of the titration is sharpened markedly if phosphoric acid is present, because Fe3+ ion produced in the titration forms an essentially colorless complex with the acid.
The number of moles of potassium permanganate used in the titration is equal to the product of the morality of the KMnO4 and the volume used. The number of moles of iron present in the samples is obtained by weight of iron in the solid sample follows directly.
Advance Study Assignment: Determination of iron by Reaction with Permanganate-A Redox Titration
1. Write the balanced net ionic equation for the reaction between Mn04 - ion and Fe2+ ion in acid solution.
2. How many moles of Fe2+ ion can be oxidized by 1.2 X l0-2 moles Mn04- ion in the reaction in Question 1?
3. A solid sample containing some Fe2+ ion weighs 1.750g. It requires 36.44 ml. 0.0244 M KMnO4 to titrate the Fe2+ in the dissolved sample to a pink end point.
a. How many moles Mn04 ion are required?
b. How many moles Fe2+ are there in the sample?
c. How many grams of iron are there in the sample?
d. What is the percent Fe in the sample?
4. What is the percent Fe in iron (II) ammonium sulfate hexahydrate, Fe(NH4 )2(S04)2* 6 H20?
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