Report – CHEM120 – Colorimetric Determination of Iron in a Vitamin Tablet using 1,10-Phenanthroline.

CHEMISTRY 120-02                                                                               2009-10-19
Colorimetric Determination of Iron in a
Vitamin Tablet using 1,10-Phenanthroline.

Stefan Martensson C0347318

Partner: Christine Meyer

Theory: To be able to measure the quantity of iron in the tablet we need to firstly assure that all the iron in the solution is in the of Fe2+ and not in Fe3+ due to the ‘blindness’ of this experiment for that ion. This is accomplished by adding Hydroquinone as a reducing agent to ensure that all iron in the solution will be in form of Fe2+.

Furthermore, to be able to view the absorption of the iron we need to enhance its very faint green colour with 1,10-Phenanthroline so it is easier to measure. Unfortunately, 1,10-Phenanthroline is only stable in the pH range of 2 to 9, and to make it stable we need to use Sodium citrate to create a buffered solution with a pH of around 3.5.

Method: Please refer to handout ‘Experiment #5’ and pages 23-26, Chemistry 120 Lab Manual, 2009 Edition, Camosun College.

Due to a slight misunderstanding in the beginning of the lab, we filtered the HCl dissolved tablet while transferring it to a 100ml vol-metric flask. We will take this into account in the discussion.

Data and Results: Temperature: 22˚C, Pressure: 762 mm Hg.

Raw Data:

Solution     Conc         Drops of Citrate   Absorbance
Unknown    X mg/l       6drops               0.75

10ml         4mg/l                5drops               0.90

5ml           2mg/l                3drops               0.45

3ml           0.12mg/l    1drop                        0.177

2ml           0.08mg/l    1drop                        0.087

Tablet fact: Made by Apptex and contains 300 mg of ferrous gluconate which delivers 35 mg of elemental iron.

Chart 1. Absorbance vs Iron Concentration

The difference in percent between the advertised value and the laboratory value is as follows:

((35mg – 33.5mg) / 35mg) * 100 =  4.29%


One major source of error we had was that we filtered twice, and some of the iron would have been caught in the first filtration and squid the data to show that it is less concentration.

The other source of error was not completely dissolving the tablet in the HCl and getting all of it out of the flask, funnel and stir stick.


We conclude that the Unknown consisted of: 33.5mg which was not too far away from the labeled concentration of 35mg

One Response to “Report – CHEM120 – Colorimetric Determination of Iron in a Vitamin Tablet using 1,10-Phenanthroline.”

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