Chemical Conclusion
Experiment 18 Chemistry 101
Redox Titration:
Determination of the Percentage of Iron in a Sample
INTRODUCTION The concentrations of redox-active species can be determined by redox titrations. In a redox titration, a measured sample of the unknown is titrated against a standard solution of a substance that will oxidize or reduce the unknown. In the present experiment you will take a sample containing iron, add acid to dissolve it [thereby converting all the iron to iron(II)], then use a solution containing permanganate ion, MnO4-, to oxidize this Fe2+ to Fe3+ ion. The percent of iron in the sample will be calculated from the amount of permanganate needed to oxidize fully all the Fe2+ ions. A solution of permanganate ion in sulfuric acid efficiently oxidizes Fe2+ to Fe3+
MnO4- + 5 Fe2+ + 8 H+ ( Mn2+ + 5 Fe3+ + 4 H20
The permanganate ion acts as its own indicator, as MnO4- is highly colored while Mn2+ is essentially colorless. The product of oxidation, the Fe3+ ion, is itself, slightly colored. To avoid any possible interference with the equivalence point determination a little phosphoric acid, H3PO4, is added so as to complex Fe3+ to a completely, colorless ion.
PROCEDURE
I. Standardization of permanganate solution Use distilled water at all times throughout the experiment. (1) Weigh three clean dry labeled 125 mL erlenmyer flasks on an analytical balance. Place about 0.135 grams of oxalic acid dihydrate, H2C204.2H20, into each of the three separate flasks and reweigh the flasks containing the acid.
(2) Set up a buret with KMnO4 solution to be standardized by titration.
(3) Dissolve each acid sample in about 25 mL of distilled water. Again don't mix up the samples. Take one flask and add 1-2 mL of concentrated sulfuric acid.
· CAUTION! Concentrated sulfuric acid is dangerous; don't spill or splash any. Always slowly add acid to water, never the other way around.
(4) The solution to which the
Redox Titration:
Determination of the Percentage of Iron in a Sample
INTRODUCTION The concentrations of redox-active species can be determined by redox titrations. In a redox titration, a measured sample of the unknown is titrated against a standard solution of a substance that will oxidize or reduce the unknown. In the present experiment you will take a sample containing iron, add acid to dissolve it [thereby converting all the iron to iron(II)], then use a solution containing permanganate ion, MnO4-, to oxidize this Fe2+ to Fe3+ ion. The percent of iron in the sample will be calculated from the amount of permanganate needed to oxidize fully all the Fe2+ ions. A solution of permanganate ion in sulfuric acid efficiently oxidizes Fe2+ to Fe3+
MnO4- + 5 Fe2+ + 8 H+ ( Mn2+ + 5 Fe3+ + 4 H20
The permanganate ion acts as its own indicator, as MnO4- is highly colored while Mn2+ is essentially colorless. The product of oxidation, the Fe3+ ion, is itself, slightly colored. To avoid any possible interference with the equivalence point determination a little phosphoric acid, H3PO4, is added so as to complex Fe3+ to a completely, colorless ion.
PROCEDURE
I. Standardization of permanganate solution Use distilled water at all times throughout the experiment. (1) Weigh three clean dry labeled 125 mL erlenmyer flasks on an analytical balance. Place about 0.135 grams of oxalic acid dihydrate, H2C204.2H20, into each of the three separate flasks and reweigh the flasks containing the acid.
(2) Set up a buret with KMnO4 solution to be standardized by titration.
(3) Dissolve each acid sample in about 25 mL of distilled water. Again don't mix up the samples. Take one flask and add 1-2 mL of concentrated sulfuric acid.
· CAUTION! Concentrated sulfuric acid is dangerous; don't spill or splash any. Always slowly add acid to water, never the other way around.
(4) The solution to which the