1. Exp. Iron in Vitamin Tablet

2. 1. Take an iron-containing vitamin tablet from the stock room.
2. Put it into a 100-ml beaker and boil gently with 25ml of 6M HCl for about 15min. (until it completely dissolves).

3. 3. Filter the solution directly into a 100-ml volumetric flask with small portion of Distilled water to wash off everything that is left in the beaker.
4. Allow the solution to cool down to room temperature.
5. Dilute to the mark, and mix it well.

4. 6. Dilute 10.00ml of unknown iron-containing solution to another 100-ml volumetric flask. (make sure to transfer enough amount of this solution)

5. 7. Pipet 10.00ml of standard Fe into a beaker.
8. Add a drop of sodium citrate solution at a time, while checking with pH paper, until it reaches about 3.5 pH.
9. Count the number of drops needed to make pH of 3.5 for standard Fe. (The purpose of this step is to make standard Fe solution acidic so that it may react with Hydroquinone later to reduce Iron ion)

6. 10. Count the number of citrate drops needed to reach pH of 3
10. Count the number of citrate drops needed to reach pH of 3.5 for unknown iron-containing solution.

7. 11. Prepare 6 100-ml volumetric flasks on the table.
12. Indicate each flask with number from 1 to 4, 5th one as a blank, and last one as an unknown.
13. Pipet 10.00ml of Fe standard solution into flask #1, 5.00ml for #2, 2.00ml for #3, 1.00ml for #4, and no Fe standard solution for blank.
14. Pipet 10.00ml of unknown iron-containing solution into the last volumetric flask.

8. 15. Add appropriate amount of citrate drops into a flask #1.
16. Drop appropriate amount (n) of citrate drops into flask #2 ~ flask #4 in proportion to the volume of Fe standard solution added to each flask.
17. Drop appropriate amount (x) of citrate drops into a unknown iron-containing volumetric flask.

10. 18. Add 2. 00ml of hydroquinone solution into each volumetric flask
18. Add 2.00ml of hydroquinone solution into each volumetric flask. (At this point, Fe 3+ is reduced to Fe 2+)

11. 19. Add 3.00ml of o-Phenanthroline solution into each volumetric flask. (At this point, Fe2+ forms color complex with o-Phenanthroline)

12. 20. Dilute each to the mark and mix all well.
21. Allow solutions to sit for enough time at least 10min. (So that it can develop a complete color complex)

13. 22. Prepare 7 cuvettes, and add each solution into a cuvette.
23. For last cuvette, put distilled water, and zero the absorbance with this at wavelength of 508nm.
24. Measure out absorbance of each.
25. Find the concentration of unknown iron-containing solution and mass of iron per tablet by using the calibration curve.

14. Question: For what reason do you use hydroquinone in measuring absorbance of Iron-containing solution?
1. to oxidize iron
2. to reduce iron
3. to form color complex
4. as a catalyst of reaction

15. Answer: 2. To reduce iron (from Fe3+ to Fe2+)