[ahhppull]

We did a lab where we took an iron tablet, dissolved it and filtered it. Then we diluted it a couple of times and found the absorbance of the solutions.

One solution had 10 mL of iron solution with 2.00 mL of hydroquinone solution and 3.0 mL of o-phenanthroline solution.

The other solution had 10 mL of iron solution and only 2.00 mL of hydroquinone solution.

The lab ta said that "some vitamins are colored with dyes that may absorb at the max of the iron complex and may yield a false absorbance value for the unknown" and "the Fe complex cannot form (without the o-phenanthroline solution) and any absorption is solely due to the dye."


My question is...I got two absorbance. What does each absorbance tell?  Do I subtract them both to get the absorbance of Fe?

[Arkcon]

Re-read your instructions critically -- it says you need the o-phenanthroline solution to get the complex that gives an absorbance for iron.  You might have a dye from the dissolved tablet that also matches the absorbance for iron.  How will you tell them apart?

[ahhppull]

I understand that without o-phenanthroline solution, the Fe complex will not form, but why does the instruction tell me to subtract the two absorbance readings?  This part confuses me.