Volumetric Determination of Iron with Potassium Permanganate
This experiment consists of titrating the ferrous ion with permanganate ion to study the oxidation-reduction reaction. The ions react in acidic solution to give ferric ion and a reduced ionic form of manganese. All the reactants and products except permanganate ion are weakly colored, whereas permanganate is a very intensely colored ion. Then a solution of permanganate is removed as long as there is a ferrous ion present to react with it. But as soon as the entire ferrous ion has been oxidized, the next small portion of added permanganate colors the solution.The first appearance of a permanent pink color indicates the endpoint of the experiment. From the titration it will be able to calculate the percentage of iron in the sample from the data.
Add 15mL of 6N sulfuric acid to a 125mL Erlenmeyer flask containing 105mL of deionized water (preparing approximately 0.75N sulfuric acid). Obtain a sample of the unknown. Weight the vial and contents accurately on an analytical balance. Handle the vial with a small strip of paper to reduce the risk of error (due to added weight). Pour about half of the sample into a clean dry 200mL Erlenmeyer flask and weight again. Use the remaining half of the sample to get a second weight of around 0.6g-0.7g. Make sure the vial is capped on every weight taken.
Rinse a 25mL buret with three 5mL portions of standard permanganate solution. Fill the buret with the standard permanganate solution and record initial and final readings.
To the first Erlenmeyer flask with the ferrous salt add about 1/3 of the 0.75N sulfuric acid. Dissolve the salt by gently swirling it in the dilute acid. Add about 5mL of the Zimmerman-Reinhardt Reagent (this reagent contains phosphoric acid which complexes yellow ferrous ions into colorless compounds which do not obscure the endpoint; it also contains manganous ions which inhibit the oxidation of any chloride ions in the sample). The use of a white background underneath the flask aids in the detecting of the endpoint. Repeat with second sample.
1st weighing, vial and sample6.042g
2nd weighing, vial and minus half of sample 5.283g
3rd weighing, vial 4.524g
Weight of samples0.759g, 0.760g
Initial buret reading of first trial 0.00mL
Final buret reading of first trial14.1mL
Initial buret reading of second trial0.00mL
Final buret reading of second trial14.4mL
0.0141L KMnO4 | 0.1001N KMnO4 | 55.85g KMnO4* 100%= 10.4% Fe
0.759g KMnO4 | 1 mol KMnO4
0.0144L KmnO4 | 0.1001N KmnO4 | 55.85 g KmnO4* 100% =10.6% Fe
0.760g KmnO4 | 1 mol KMnO4
From the equations below it is possible to obtain the oxidation state of reduced ionic form
5Fe+25Fe+3+ 5e-oxidation reaction
MnO4-1 + 5e- + 8H+1Mn+2 + 4H2Oreduction reaction
5Fe+2 + MnO4-1+ 8H+15Fe+3 + Mn+2+ 4H2O
The reduced ionic form of manganese is Mn+2.The equation showsMnO4-1
decomposes into Mn+2, in the reduction equation, which in turn is the reduced ionic form