Erlenmeyer flasks, 250-mL, 3
Potassium permanganate, KMnO,, ~ 0 . 0 2 , 100 mL
Ferrous ammonium sulfate, Fe(NH4)2S04.6H20,.100 M, 50 m L
Volumetric pipet, 10-mL
Oxalic acid solution, HzC204, 0 mL
Volumetric pipet, 25-mL
Sulfuric acid, H2S04,6 M, 50 mL
Beakers, 100-mL, 3
Manganese sulfate, MnS04.Hz0,1.0 M, 5 mL
Graduated cylinder, 10-mL
Water, distilled or deionized
S afety Precautions
Sulfuric acid ( 6 M ) is corrosive to eyes, skin, and other tissue; always add acid to water, never the reverse. Potassium permanganate solution may be a skin irritant. The oxalic acid solution is a skin and eye irritant; it is moderately toxic by ingestion. The manganese sulfate solution is a body tissue irritant. Wear chemical splash goggles and chemical-resistant gloves and apron. Wash hands thoroughly with soap and water before leaving the laboratory.
Part 7. Standardization of a Potassium Permanganate Solution 1. Obtain approximately 80 mL of Ihe potassium permanganate solution in a 100-mL beaker. s
Obtain 50 mL of the 0.100 M Fez+ olution in another 100-mL beaker. Label both beakers. 2. Set up a clean, 50-mL buret in the ring stand and buret clamp.
3. Rinse the buret with approximately 10 mL of distilled or deionized water and then with two 5 m L portions of the M n 0 4solution.
4. Close the stopcock and fill the buret to above the zero mark with M n 0 4solution. 5. Open the stopcock to allow any air bubbles to escape from the tip. Close the stopcock when the liquid level is between the 0- and 10-mL marks.
6. Record the precise level of the solution in the buret in the Part 1 Data Table. This is the initial volume of the M n 0 4solution. (See Figure 1 for reading buret level.)
7. With the volumetric pipet, transfer 10 mL of the 0.100 M Fez+ solution to a clean 250-mL Erlenmeyer flask. Record this volume in the Part 1 Data Table.
8. Measure out 10 mL of the 6 M HzS04into a clean 10-mL graduated cylinder and add this to the Erlenmeyer flask. Swirl to mix.
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9. Position the flask under the buret so that the tip of the buret is within the flask but at least 2 cm above the liquid surface.
10. Titrate the ~ e'' solution with the M n 0 4 solution until the first trace of pink color persists for 30 seconds. Remember to swirl the flask and to rinse the walls of the flask with distilled water before the endpoint is reached.
11. Record final buret reading as the final volume of the M n 0 4 solution in the Part 1 Data Table. 12. Repeat the standardization titration two more times.
P art 2. Determination of Concentration of an Oxalic Acid Solution
1. Obtain approximately 60 mL of the oxalic acid solution in a clean 100-mL beaker. 2. With a 25-mL volumetric pipet, transfer 25 mL samples of the oxalic acid solution to each of two 250-mL Erlenmeyer flasks. Record the volume in the Part 2 Data Table. 3. Add 5 drops of the 1.0 M M nS04solution to each flask. ( The ~ n ' ion acts as a catalyst for +
4. Measure out 10 mL of 6 M H 2S04into a graduated cylinder and add this amount to each of the 250-mL Erlenmeyer flasks. Add 20 mL of distilled water to each flask and swirl.
5. Warm the first flask to about 85 "C on the hot plate.