Redox Titration Lab
In this lab, 0.010 M purple-colored potassium permanganate solution was standardized by redox titration with iron (II) ammonium sulfate hexahydrate (FAS). The average mass of the three flasks of FAS was 0.483 grams. Once the concentration of the standard solution of KMnO4 (aq) was determined, it was used to determine the concentration of Fe2+ in iron pills. On average, there was 0.01813 L of solution used. With this information and the balanced net-ionic equation 10Fe(NH4)2(SO4)2*6H2O+2KMnO4+H2SO4 --> 5Fe2(SO4)3+(NH4)2SO4+K2SO4+2MnSO4+H2O, the average percentage by mass composition of Fe2+ in iron pill samples was 16.99%. (103) INTRODUCTION:
The scientific concept of this lab was to titrate potassium permanganate with iron (II) ammonium sulfate hexahydrate in order to oxidize the Fe2+ to Fe3+. Then the concentration of the standard solution of KMnO4 (aq) will be used to determine the concentration of Fe2+ in iron pills. The purpose of the lab is to first standardize a stock KMnO4 (aq), and then determine the percentage Fe2+ in iron pills. The expected outcome of this lab was for the percentage of Fe2+ in the iron pills to be 17%. This is what was on the bottle of iron pills, and the point of the lab was to use titration to retrieve as much if the iron as possible. MATERIALS AND METHODS:
The procedure for the standardization of KMnO4 (aq) was to first fill a clean 50 mL buret with 0.0100 M KMnO4 (aq). Three clean Erlenmeyer flasks needed to be labeled, and a piece of FAS needed to be weighed to 0.5g on a piece of weighing paper. Flask 1 was tarred and tapped into the FAS. The mass was then recorded. This was then repeated with flask 2 and 3. 10 mL of water and 5 mL of 3M H2SO4 was added to the three flasks. 50 mL of water was put in a beaker and 1 drop of permanganate solution was added. The color intensity of the mixture matched the standard and remained for 5 seconds or more. The initial volume was recorded to 0.01 mL. Permanganate was then added to the FAS solution in flask 1 until the equivalent point was reached. The final volume was recorded and the permanganate solution used was determined. The titration process was repeated using FAS in flask 2 and 3. The flasks were then washed down the drain and rinsed with distilled water. Moles of Fe2+ ions present was calculated from the mass of FAS. The balanced equation was used to find the moles of KMnO4 needed to reach the same point. The three molarities of the permanganate solutions were then calculated. The molarities were added to the class data which would calculate the overall molarity for permanganate solutions.
The procedure for the analysis of the iron pill was to first grind 2 iron pills in a mortar and pistol. There was 63 mg of iron per pill. 0.3 grams was weighed on weighing paper, and an Erlenmeyer flask was tarred. The powder was then put in the flask and massed to 0.001 g. This was then repeated with the second sample. 25 mL water, 15 mL 3M H2SO4, and a few drops of H3PO4(aq) was added to each flask and swirled until the iron pill was dissolved. The initial volume of the reading in the buret was recorded, and permanganate was added to the iron pill solution in flask 1 until the same point is reached. The final volume reading was recorded, and the exact volume of the permanganate used was found. The titration process was repeated using the iron pill in flask 2. The mixtures in flasks were washed down the drain, and the flasks were rinsed with water. The buret was rinsed with tap water and the stopcock was open for storage. RESULTS:
FAS mass Flask #1: 0.500 g
tarred: 0.485 g
FAS mass Flask #2: 0.501 g
tarred: 0.496 g
FAS mass Flask #3: 0.497 g
tarred: 0.467 g
KMnO4 |Initial V (mL) |Final V (mL) |Solution used (mL) | |Titration #1 |0.01 |25.45 |25.44 | |Titration #2 |0.00 |26.36 |26.36 | |Titration #3 |0.00 |24.31 |24.31 | |Iron Pills:
Iron Pill mass Flask #1: 0.286 g
Iron Pill mass Flask...
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