The purpose of this experiment is to analyze iron content of an unknown solution by reduction-oxidation titration with a standardized permanganate solution.
Conditions of Redox Analysis
Redox titration is based on reduction and oxidation, it is similar to acid-bade titration if the four principles are met:
1 The reaction is thermodynamically spontaneous enough to be stoichiometric
2 The reaction is usually fast to produce an immediate result
3 There is no other reaction that occurs
4 There is an adequate indicator (Burk, 84)
Analysis of Fe2+ by Redox Titration:
By these principles, the titration of Fe (II) solutions with different redox reagents is easy. As ...view middle of the document...
Standardization of Permanganate Solutions
The KMnO4 oxidizes spontaneously to MnO2 because it is not standardized and sodium oxalate is used so that the concentration can be known and standardize it.
The reaction equation:
16H3O+(aq) + 5C2O42-(aq) + 2MnO4-(aq) - 2Mn2+(aq) + 10CO2(aq) + 24H2O(l)
Reducing agent C2O42: C2O42- 2CO2 + e-
Oxidizing agent MnO4- : MnO4- + 8H3O+ 5e- Mn2+ + 12H2O
The KMnO4 solution is filtered in order to get rid of all the solid MnO2 that is present in the solution interfering the standardization of KMnO4. Titration begins at room temperature because the hot sodium oxalate is left open to air in the presence of acid and this causes it to decompose by producing water and peroxide. 1M H2SO4 is titrated as blank is to ensure it turns pink and to test for the end point of the blank solution.
Part I â€“Standardization of KMnO4
The solution of 0.02M KMnO4 was prepaid before the lab. 1000ml of water was added into a 1000ml Erlenmeyer flask. Then 55ml of H2SO4 concentration was added into the 1000ml Erlenmeyer flask with the water. 0.2140g and 0.2729 of sodium oxalate was weighed by difference from an analytic balance into a 500ml Erlenmeyer flask. 50ml of 1.0M H2SO4 from the 1000ml Erlenmeyer was added to each samples of Na2C2O4 in the 500ml Erlenmeyer flask. The solutions were swirled and Stirring rod was used to dissolve large chunks of Na2C2O4. Permanganate in the burette was added to the solution to consume 90 to 95% of the oxalate by swirling until it is colourless. In order to calculate the volume of 90% of KMnO4 needed the below equation was used:
Vol 90% KNmO4 (ml) =() x 0.9 x 1000ml/l
The three solutions were heated up to 55 and titrated until a pink pale colour was discovered which is the end point. The volumes were recorded. In order to test for the end point of the blank, a single drop of KMnO4 was added to 1.0M H2SO4 and it turned pink immediately.
Part II-Determination of the Fe2+ content of an unknown
A numbered sample of iron ore was obtained and the sample number was recorded. 1.4951g and 1.5693 of iron ore was weighed by difference from an analytic balance into a 250ml Erlenmeyer flask. Distilled water, 10ml of 3M H2SO4, and 2ml of H3PO4 was added to dissolve the samples. Standardized KMnO4 solution was titrated into each sample, taking the end point as the fainted shade pink that appears in the solution during titration.
Table1:- Standardization of KMnO4
Physical description of dried Na2C2O4
White, powdery substance
Physical description of solution when 250mL of 1M H2SO4 was added to each sample already containing weighed Na2C2O4
Colour change of the titration solution during â€œthe standardization of KMnO4â€
Pale pink colour
Table 2- Weight of Sodium Oxalate (Na2C2O4)
Table 3- Titration Volume from the Burette