Redox Titration: Standardization of Kmno4 & the % Fe2+ in Iron Pills

2+ Redox Titration: Standardization of KMnO4 & the % Fe in Iron Pills

Background: Redox titration is a process used to determine the concentration of an ion in an unknown solution by reacting it with another ion in a solution having a known concentration. The equivalence point is reached when the total number of electrons lost in the oxidation reaction is equal to the total number of electrons gained in the reduction reaction. In this experiment, a purple-colored solution of potassium permanganate with an approximate concentration of 0.02 M will be added to a solution containing Fe2+ ions. The permanganate ions -1 3+ (MnO4 ) are a strong oxidizing agent which causes the iron to be oxidized to Fe ions. The manganese is reduced from a 7+ oxidation state in the permanganate ion to form colorless Mn2+ ions. The equivalence point is indicated at the point when all of the Fe2+ ions in solution are oxidized and the colorless mixture retains a 2+ purple tint. (This color may be more orange in appearance, depending upon the concentration of the Fe (aq), which has a yellow-green tint. A few drops of concentrated phosphoric acid can be added to form a complex with the iron and minimize this color.) Sulfuric acid is added to increase the concentration of hydrogen ions in the solution. Caution: Potassium permanganate and sulfuric acid can cause chemical burns. The KMnO4 will stain skin and clothing. Avoid skin contact with these chemicals.

1-- Problem: Can you determine the molarity of the MnO4 ions in a solution by performing a redox titration?

Standardization of KMnO4: Use no more than 2g of your primary standard, iron (II) ammonium sulfate hexahydrate (abbreviated FAS), Fe(NH4)2(SO4)2•6H2O, to standardize two samples of the potassium permanganate solution. Tip 1: Add 25 mL of distilled water, 15 mL of 3M H2SO4, and a few drops of concentrated H3PO4(aq) to each flask and swirl to dissolve the FAS. Tip 2: Place about 50 mL of water in a beaker and add 1 drop of the permanganate solution. This is the color standard for the reaction. When the equivalence point is reached, the color intensity of the mixture should match this standard.

Analysis of the Iron Pill: Use no more than 5 iron pills, a mortar and pestle, distilled water, 3M H2SO4, concentrated H3PO4(aq) to prepare two samples for analysis.

Disposal: Drain any excess KMnO4 into the waste beaker, rinse the buret with 10 mL of tap water, then add the washing to the beaker. Add a small scoop of sodium hydrogen sulfite, NaHSO3, to the waste beaker and stir to reduce 2+ the KMnO4 to colorless Mn . Rinse this colorless solution down the drain and rinse with plenty of water.

Results and Conclusions: 1. Write a balanced equation for the redox reaction that occurs in both parts of the experiment. 2. Determine the molarity of the potassium permanganate solution. 3. Determine the mass percent of Fe2+ in the iron pills. 4. Analyze the accuracy and precision of your results. The manufacturer claims that there are 65 mg of Fe2+ per pill. 5. Analyze your data for the experiment in the spreadsheet and compare your results to the class data. Should any values by excluded by the Q test? (If you don’t know it, look it up. If you decide yes, show calculation)