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This is from a lab: DETERMINATION OF THE IRON CONTENT OF A DIETARY SUPPLEMENT A.) Calculate the molarity of the standardized permanganate solution. B.) Calculate the mass content of Fe (in mg) per tablet. Procedure of lab: 1. Preparation of 0.002 M potassium permanganate: Use one of the large beakers for this preparation. Permanganate solutions are heated first to destroy reducible substances (traces of organics remaining in deionized water). After cooling, decant the supernatant to an amber bottle to get rid of the manganese dioxide impurities. If the solution is kept in the dark and is not acidified, its concentration will remain stable for several weeks. Procedure: Dissolve about 0.32 g of KMnO4 (F.W. 158.034 g/mol) in 1 L of deionized water using a large beaker. Cover that beaker with a watch-glass and heat to boiling using a hot plate in the hood. Keep the solution at a gentle boil for about 1 hr. Let the solution cool and transfer the supernatant of the solution to a clean amber glass-stoppered bottle (if you do not have it, use a regular glass bottle, then wrap it with aluminum foil); store in the dark when not in use. 2. Standardization of the potassium permanganate solution: Procedure: Weigh about three portions of 0.015 g dry sodium oxalate, Na2C2O4 samples (to the nearest 0.1 mg) and transfer a sample into a beaker or conical flask. Dissolve each sample in about 65 mL of 6M H2SO4. Fill a clean buret with the KMnO4 solution (make sure to rinse the buret three times with a few milliliters of the KMnO4 solution and dispose of the used KMnO4 in the appropriate waste container). Heat each solution to 80-90Â°C, and titrate with KMnO4 while stirring with a thermometer. The temperature should not drop below 60Â°C. The end point is marked by the appearance of a faint pink color that persists at least 30 s. Record the titration data, and calculate the concentration of the permanganate solution. Notes: 1. During the titration, promptly wash down any KMnO4 that spatters on the walls of the beaker into the bulk of the liquid using a wash bottle. 2. Finely divided MnO2 will form if the KMnO4 is added too rapidly and will cause the solution to acquire a faint brown discoloration. This is not a serious problem if sufficient oxalate remains to reduce the MnO2 to Mn2+; simply discontinue the titration until the brown color disappears. 3. The surface of the permanganate solution rather than the bottom of the meniscus can be used to measure titrant volumes if you encounter difficulty reading. 4. Partial decomposition of the permanganate to MnO2 may occur if it remains in the buret for a long time. Clean the buret with a dilute sodium bisulfite solution. 3. The Determination of Iron in a supplement tablet: Grind two iron supplement tablets to a fine powder by using a mortar and pestle as fine powder as possible, and transfer to a 250-mL beaker. Add about 50 mL of 1 M sulfuric acid solution and stir for approximately 30 min to dissolve it completely. Quantitatively transfer the resulting solution into a 100 mL volumetric flask and make up to volume with 1 M sulfuric acid solution (be careful not to overfill). Titrate three 10-mL aliquots of the sample solution with the potassium permanganate solution to the first faint pink that persists for 30 s. Do not add the KMnO4 rapidly at any time. Save the rest of the unknown sample solution (in the original 100 mL flask) for Lab 7. Part A was solved: The average Molarity calculated was 0.002099 M. Part B: Results of iron solution titrated (2 iron tablets, 100 mL of sulfuric acid): (Note: only 10 mL of this solution was used) Trial 1: Initial reading, mL: 23.80 mL Final reading, mL: 44.22 mL Vol. of titrant, mL: 20.42 mL Trial 2: Initial reading, mL: 4.85 mL Final reading, mL: 25.30 mL Vol. of titrant, mL: 20.45 mL Trial 3: Initial reading, mL: 25.30 mL Final reading, mL: 45.60 mL Vol. of titrant, mL: 20.30 mL Equation: 5Fe2+ + MnO4- + 8H+ â†’ 5Fe3+ + Mn2+ + 4H2O According to the reaction equation given above, 1 mole of permanganate reacts with 5 moles of iron, and this ratio has to be used for titration result calculation.

This is from a lab: DETERMINATION OF THE IRON CONTENT OF A DIETARY SUPPLEMENT

A.) Calculate the molarity of the standardized permanganate solution.

B.) Calculate the mass content of Fe (in mg) per tablet.

Procedure of lab:

1. Preparation of 0.002 M potassium permanganate: Use one of the large beakers for this preparation. Permanganate solutions are heated first to destroy reducible substances (traces of organics remaining in deionized water). After cooling, decant the supernatant to an amber bottle to get rid of the manganese dioxide impurities. If the solution is kept in the dark and is not acidified, its concentration will remain stable for several weeks.

Procedure: Dissolve about 0.32 g of KMnO4 (F.W. 158.034 g/mol) in 1 L of deionized water using a large beaker. Cover that beaker with a watch-glass and heat to boiling using a hot plate in the hood. Keep the solution at a gentle boil for about 1 hr. Let the solution cool and transfer the supernatant of the solution to a clean amber glass-stoppered bottle (if you do not have it, use a regular glass bottle, then wrap it with aluminum foil); store in the dark when not in use.

2. Standardization of the potassium permanganate solution:

Procedure: Weigh about three portions of 0.015 g dry sodium oxalate, Na2C2O4 samples (to the nearest 0.1 mg) and transfer a sample into a beaker or conical flask. Dissolve each sample in about 65 mL of 6M H2SO4. Fill a clean buret with the KMnO4 solution (make sure to rinse the buret three times with a few milliliters of the KMnO4 solution and dispose of the used KMnO4 in the appropriate waste container). Heat each solution to 80-90Â°C, and titrate with KMnO4 while stirring with a thermometer. The temperature should not drop below 60Â°C. The end point is marked by the appearance of a faint pink color that persists at least 30 s. Record the titration data, and calculate the concentration of the permanganate solution.

Notes:

1. During the titration, promptly wash down any KMnO4 that spatters on the walls of the beaker into the bulk of the liquid using a wash bottle.

2. Finely divided MnO2 will form if the KMnO4 is added too rapidly and will cause the solution to acquire a faint brown discoloration. This is not a serious problem if sufficient oxalate remains to reduce the MnO2 to Mn2+; simply discontinue the titration until the brown color disappears.

3. The surface of the permanganate solution rather than the bottom of the meniscus can be used to measure titrant volumes if you encounter difficulty reading.

4. Partial decomposition of the permanganate to MnO2 may occur if it remains in the buret for a long time. Clean the buret with a dilute sodium bisulfite solution.

3. The Determination of Iron in a supplement tablet:

Grind two iron supplement tablets to a fine powder by using a mortar and pestle as fine powder as possible, and transfer to a 250-mL beaker. Add about 50 mL of 1 M sulfuric acid solution and stir for approximately 30 min to dissolve it completely. Quantitatively transfer the resulting solution into a 100 mL volumetric flask and make up to volume with 1 M sulfuric acid solution (be careful not to overfill). Titrate three 10-mL aliquots of the sample solution with the potassium permanganate solution to the first faint pink that persists for 30 s. Do not add the KMnO4 rapidly at any time. Save the rest of the unknown sample solution (in the original 100 mL flask) for Lab 7.

Part A was solved: The average Molarity calculated was 0.002099 M.

Part B:

Results of iron solution titrated (2 iron tablets, 100 mL of sulfuric acid):

(Note: only 10 mL of this solution was used)

Trial 1:
Initial reading, mL: 23.80 mL
Final reading, mL: 44.22 mL
Vol. of titrant, mL: 20.42 mL

Trial 2:
Initial reading, mL: 4.85 mL
Final reading, mL: 25.30 mL
Vol. of titrant, mL: 20.45 mL

Trial 3:
Initial reading, mL: 25.30 mL
Final reading, mL: 45.60 mL
Vol. of titrant, mL: 20.30 mL

Equation:
5Fe2+ + MnO4- + 8H+ â†’ 5Fe3+ + Mn2+ + 4H2O

According to the reaction equation given above, 1 mole of permanganate reacts with 5 moles of iron, and this ratio has to be used for titration result calculation.

Added by Melinda B.

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