Redox Titration of Iron
Wiley Turner
Liam Doyle, and Liam Springer
The Packer Collegiate Institute, 170 Joralemon Street, Brooklyn, New York, 11201
Performed on November 10th and 13th, 2017
Due on December 6th, 2017
Liam Doyle, and Liam Springer
The Packer Collegiate Institute, 170 Joralemon Street, Brooklyn, New York, 11201
Performed on November 10th and 13th, 2017
Due on December 6th, 2017
Objective:
The objective of this lab was to determine the amount of iron in an iron supplement bought from Duane Reade by using the amount of permanganate solution that reacted with the tablet to calculate the amount of iron in the tablet. In the process of doing this, we also familiarized ourselves with the titration, a process often used in advanced experiments.
Pre-lab Questions:
1.
Fe2+(aq) + MnO4-(aq) --> Fe3+(aq) + Mn2+(aq)
Iron is being oxidized, going from a +2 charge to a +3 charge and losing an electron.
Manganese is being reduced, going from a +3 charge to a +2 charge and gaining an electron.
Oxidation
5(Fe2+--> Fe3+ + e- )
Reduction
5e- + 8H+ + MnO4- --> Mn2+ + 4H2O
Balanced
5Fe2+(aq) + 8H+ (aq)+ MnO4- (aq)--> Mn2+ (aq)+ 4H2O (l)+ 5Fe3+ (aq)
Post-Lab Questions:
1.
This would affect our reaction because it would mean that the permanganate reacts with another metal in the solution. Due to this, it would take more permanganate to fully react and the titration would indicate a larger volume of permanganate solution used. Using this larger volume in the calculation, we would find that there was a larger amount of iron in the tablet.
2.
Because we crushed up our tablet, the green coating would not affect the results of the titration. However, if we decided not to crush up the tablet, no reaction between the iron in the tablet and the permanganate solution would occur because of the nonreactive green coating covering the iron. Consequently, our results would indicate that there is no iron in the tablet.
3.
Sulfuric acid was added before titration because the iron from the tablet reacts in a redox reaction with the permanganate in an acidic environment (5Fe2++ 8H+ + MnO4- --> Mn2+ + 4H2O + 5Fe3+). The sulfuric acid provides the redox reaction with the H+ cation and in the process of the reaction, the hydrogen cation from the acid is consumed and turned into water.
4a.
The student affects the results of the experiment because in the adding of the distilled water, they changed the molarity of the permanganate solution and made it more dilute. In turn, this would affect the amount of titrated solution as it would take more solution to react with the same amount of iron. When plugging the new value into their calculations, they would find that there was more iron in the tablet than there actually was due to this error.
4b.
The student affects the results of the experiment because by leaving the solution exposed to the air, they allow for the iron to be oxidized. While it is likely that all of the iron would not oxidize, a noticeable amount would, taking away from the amount of iron that reacts with the titrated permanganate solution. Because of this decreased value of iron, it would take a lower volume of permanganate solution to fully react. When plugging the new number moles of permanganate into his calculations, they would find that there was less iron in the tablet than there actually was due to the other remaining iron from the tablet being oxidized.
4c.
The student affects the results of the experiment because by not getting all of the tablet residue off the sides of the flask, they do not get all the iron from the tablet into the flask. This means that, due to the decrease in iron, it will take less permanganate solution to react with the iron in the flask and the volume of the solution from the titration will decrease. When plugging the new number of moles of permanganate into their calculations, they would find that there was less iron in the tablet than there actually was due to the other remaining iron from the tablet being left on the side of the flask.
The objective of this lab was to determine the amount of iron in an iron supplement bought from Duane Reade by using the amount of permanganate solution that reacted with the tablet to calculate the amount of iron in the tablet. In the process of doing this, we also familiarized ourselves with the titration, a process often used in advanced experiments.
Pre-lab Questions:
1.
Fe2+(aq) + MnO4-(aq) --> Fe3+(aq) + Mn2+(aq)
Iron is being oxidized, going from a +2 charge to a +3 charge and losing an electron.
Manganese is being reduced, going from a +3 charge to a +2 charge and gaining an electron.
Oxidation
5(Fe2+--> Fe3+ + e- )
Reduction
5e- + 8H+ + MnO4- --> Mn2+ + 4H2O
Balanced
5Fe2+(aq) + 8H+ (aq)+ MnO4- (aq)--> Mn2+ (aq)+ 4H2O (l)+ 5Fe3+ (aq)
Post-Lab Questions:
1.
This would affect our reaction because it would mean that the permanganate reacts with another metal in the solution. Due to this, it would take more permanganate to fully react and the titration would indicate a larger volume of permanganate solution used. Using this larger volume in the calculation, we would find that there was a larger amount of iron in the tablet.
2.
Because we crushed up our tablet, the green coating would not affect the results of the titration. However, if we decided not to crush up the tablet, no reaction between the iron in the tablet and the permanganate solution would occur because of the nonreactive green coating covering the iron. Consequently, our results would indicate that there is no iron in the tablet.
3.
Sulfuric acid was added before titration because the iron from the tablet reacts in a redox reaction with the permanganate in an acidic environment (5Fe2++ 8H+ + MnO4- --> Mn2+ + 4H2O + 5Fe3+). The sulfuric acid provides the redox reaction with the H+ cation and in the process of the reaction, the hydrogen cation from the acid is consumed and turned into water.
4a.
The student affects the results of the experiment because in the adding of the distilled water, they changed the molarity of the permanganate solution and made it more dilute. In turn, this would affect the amount of titrated solution as it would take more solution to react with the same amount of iron. When plugging the new value into their calculations, they would find that there was more iron in the tablet than there actually was due to this error.
4b.
The student affects the results of the experiment because by leaving the solution exposed to the air, they allow for the iron to be oxidized. While it is likely that all of the iron would not oxidize, a noticeable amount would, taking away from the amount of iron that reacts with the titrated permanganate solution. Because of this decreased value of iron, it would take a lower volume of permanganate solution to fully react. When plugging the new number moles of permanganate into his calculations, they would find that there was less iron in the tablet than there actually was due to the other remaining iron from the tablet being oxidized.
4c.
The student affects the results of the experiment because by not getting all of the tablet residue off the sides of the flask, they do not get all the iron from the tablet into the flask. This means that, due to the decrease in iron, it will take less permanganate solution to react with the iron in the flask and the volume of the solution from the titration will decrease. When plugging the new number of moles of permanganate into their calculations, they would find that there was less iron in the tablet than there actually was due to the other remaining iron from the tablet being left on the side of the flask.
Conclusion:
Overall, we were generally successful in using titration to confirm the amount of iron in the tablet. Titration is a technique used to find a value of molarity of a solution being titrated or the amount of reactant in a substance titrated into. In the first part of the experiment, we determined the molarity of a potassium permanganate solution by titrating the solution into a substance with a known amount of iron (FAS), measuring the change of volume of potassium permanganate solution once the iron had fully reacted (11.0 mL), and using this volume in our calculations to find the molarity. We found that the molarity of our solution was 0.00927 M. In the second part of the experiment, we used this new molarity of the potassium permanganate solution and titrated it into a substance with an unknown amount of iron (ferrous sulfate tablet). This was done in order to determine the amount of iron in the substance. We ended up using the first trial as we had slightly overshot the second trial. In the first trial, we titrated 21.8 mL of the potassium permanganate solution into the substance and through calculations found that there was 56.5 milligrams of iron in the tablet. This recovery gave us percent uncertainty of 13% when compared to the 65 milligrams of iron that was advertised by Duane Reade.
While this experiment was successful, the results were not everything that we had hoped for and there are many errors that could have affected the results of our experiment in negative ways. One source of error that we found was the fact that we may have misjudged the color of our titrated solution in both parts of the lab. By misjudging the color of the FAS solution in the first part, we would have standardized the KMnO4 incorrectly and wouldn’t have gotten the correct molarity of the solution. In turn, the incorrect molarity would affect the second part of the lab, as our calculations would indicate that either more or less KMnO4 than the actual amount would have reacted with the tablet due to our incorrectly standardized solution. Not only would the molarity of the KMnO4 solution affect the second part of the experiment, but if we had misjudged the color of the titrated tablet solution, we would be lead to believe that either more or less KMnO4 than the actual amount would have reacted with the tablet, causing our calculations to be even more wrong.
Another error was the fact that we may have also diluted the solution by adding too much water to the Erlenmeyer flask in both parts. In doing this, we added more particles to the respective solutions of iron and may have decreased the reaction rate as there would be less collisions between the dissociated iron and permanganate. Because of the slowed reaction rate, the purple color of the unreacted potassium permanganate may have stayed in our solution for longer after being titrated leading us to stop the titration prematurely. This stop would have lead to a higher molarity in the first part as it would appear that less potassium permanganate solution was used to react with the FAS. In the second part, it would have lead to a lower amount of iron as it would appear to take less of the standardized solution to react with the iron in the tablet, thus through calculations we would find a lower amount of iron. This could explain how we were only able to confirm 87% of the iron from the tablet.
In addition to fixing the errors in our experiment, there are also other ways that we could improve our experiment. For one, we could use a stir bar during titration in part two in order to continuously stir the iron tablet solution and the titrated potassium permanganate solution. In doing this, we would be able to make sure that the potassium permanganate gets spread around the solution and is able to react with all the iron so that the purple color does not appear to stay due to the fact that it is not coming into contact with the iron. With this change, the potassium permanganate would react quicker causing the purple color to disappear quicker. When the iron has fully reacted, we would be able to clearly tell that the purple color is no longer dissipating and would be able to quickly stop the titration, thus recording a more accurate measurement for the amount of potassium permanganate solution used. With these changes, we would be able to get a more accurate value of iron in the tablet and our lab would be overall more successful.
Citations:
POTASSIUM PERMANGANATE. (n.d.). Retrieved December 5, 2017, from https://pubchem.ncbi.nlm.nih.gov/compound/potassium_permanganate
Overall, we were generally successful in using titration to confirm the amount of iron in the tablet. Titration is a technique used to find a value of molarity of a solution being titrated or the amount of reactant in a substance titrated into. In the first part of the experiment, we determined the molarity of a potassium permanganate solution by titrating the solution into a substance with a known amount of iron (FAS), measuring the change of volume of potassium permanganate solution once the iron had fully reacted (11.0 mL), and using this volume in our calculations to find the molarity. We found that the molarity of our solution was 0.00927 M. In the second part of the experiment, we used this new molarity of the potassium permanganate solution and titrated it into a substance with an unknown amount of iron (ferrous sulfate tablet). This was done in order to determine the amount of iron in the substance. We ended up using the first trial as we had slightly overshot the second trial. In the first trial, we titrated 21.8 mL of the potassium permanganate solution into the substance and through calculations found that there was 56.5 milligrams of iron in the tablet. This recovery gave us percent uncertainty of 13% when compared to the 65 milligrams of iron that was advertised by Duane Reade.
While this experiment was successful, the results were not everything that we had hoped for and there are many errors that could have affected the results of our experiment in negative ways. One source of error that we found was the fact that we may have misjudged the color of our titrated solution in both parts of the lab. By misjudging the color of the FAS solution in the first part, we would have standardized the KMnO4 incorrectly and wouldn’t have gotten the correct molarity of the solution. In turn, the incorrect molarity would affect the second part of the lab, as our calculations would indicate that either more or less KMnO4 than the actual amount would have reacted with the tablet due to our incorrectly standardized solution. Not only would the molarity of the KMnO4 solution affect the second part of the experiment, but if we had misjudged the color of the titrated tablet solution, we would be lead to believe that either more or less KMnO4 than the actual amount would have reacted with the tablet, causing our calculations to be even more wrong.
Another error was the fact that we may have also diluted the solution by adding too much water to the Erlenmeyer flask in both parts. In doing this, we added more particles to the respective solutions of iron and may have decreased the reaction rate as there would be less collisions between the dissociated iron and permanganate. Because of the slowed reaction rate, the purple color of the unreacted potassium permanganate may have stayed in our solution for longer after being titrated leading us to stop the titration prematurely. This stop would have lead to a higher molarity in the first part as it would appear that less potassium permanganate solution was used to react with the FAS. In the second part, it would have lead to a lower amount of iron as it would appear to take less of the standardized solution to react with the iron in the tablet, thus through calculations we would find a lower amount of iron. This could explain how we were only able to confirm 87% of the iron from the tablet.
In addition to fixing the errors in our experiment, there are also other ways that we could improve our experiment. For one, we could use a stir bar during titration in part two in order to continuously stir the iron tablet solution and the titrated potassium permanganate solution. In doing this, we would be able to make sure that the potassium permanganate gets spread around the solution and is able to react with all the iron so that the purple color does not appear to stay due to the fact that it is not coming into contact with the iron. With this change, the potassium permanganate would react quicker causing the purple color to disappear quicker. When the iron has fully reacted, we would be able to clearly tell that the purple color is no longer dissipating and would be able to quickly stop the titration, thus recording a more accurate measurement for the amount of potassium permanganate solution used. With these changes, we would be able to get a more accurate value of iron in the tablet and our lab would be overall more successful.
Citations:
POTASSIUM PERMANGANATE. (n.d.). Retrieved December 5, 2017, from https://pubchem.ncbi.nlm.nih.gov/compound/potassium_permanganate
