# Finding amount of iron from absorbance

• Puchinita5
In summary, the conversation discusses the process of determining the amount of iron present in a vitamin through dilutions and calculations. After correcting a few errors in the calculations, it is determined that the amount of iron present in the vitamin is approximately 64 mg, which aligns with the amount found in a similar vitamin on the market.
Puchinita5
So I had a lab where we are supposed to determine the amount of iron present in a vitamin.

I have a calibration curve already constructed, and it is telling me that the concentration of the iron is about 3.20 ppm.

The vitamin was boiled with acid, filtered, and diluted to 100mL.
Then, 5mL of this solution was diluted to 100mL.
Then, 10mL of this already diluted solution was diluted to 100mL (after being mixed with hyroquinone and o-phenanthroline to create a red complex)

So my question is, how to figure out how much iron was present with all these dilutions.

My guess is to say that

3.20 ppm *(1g/10^6 micro g) * (1000 mL/ L) *(1 mol Fe / 55.8 g Fe) = 5.7 x 10^-5 M (molarity)

and then

5.7 x 10^-5 M * (100 mL / 10 mL) * (100 mL / 5mL) * 100mL = 1.15 mol Fe = 64 g of Fe.

But to me this seems like a lot of iron to be present in one tiny tablet.

What am I doing wrong? Or is this right?

3.20 ppm of Fe3+ = 320mg/L Fe3+ = 0.320g/L Fe3+ (divide by molar mass)

(0.320g/L)/(55.84g/mol) = 0.0057 mol/L -------> 5.7 * 10^-3 Molar Fe3+ ...(are you doing your math correctly?)

I think 3.20 ppm is = to 3.20 mg/L not 320 mg/L .

I did notice that in my second step, I was multiplying by 100 mL instead of .1 L so the units were off. So I think it should be

5.7 x 10^-5 M * (100 mL / 10 mL) * (100 mL / 5mL) * (.100 L) = .001146 mol Fe = 64 mg of Fe.

I think this sounds more reasonable? And I just tried googling it and I found a vitamin on the market that has 65 mg of iron in it (and looks like the pill I used in the experiment). So I'm thinking that maybe this is correct.

I got 64 mg as well, but as I didn't bothered to use paper/calculator I could make some mistake. But it is unlikely that we both made the same mistake - so 64 mg looks quite probable.

I would first commend you on your thorough approach in determining the amount of iron present in the vitamin. Your calculations seem to be correct based on the given information, but there could be a few things to consider.

Firstly, it is important to ensure that all measurements and dilutions were done accurately and precisely to get an accurate result. Any errors in measurement or dilution could affect the final calculated amount of iron.

Secondly, the calibration curve you used may have some inherent error, which could also contribute to the discrepancy in the calculated amount of iron. It is always advisable to repeat the experiment multiple times and take an average to minimize any potential error.

Lastly, it is important to consider the source and composition of the vitamin. Different brands and types of vitamins may have varying amounts of iron. It is also possible that the vitamin contains other compounds that could interfere with the iron measurement, leading to an overestimation of the iron content.

In conclusion, your calculations seem to be correct based on the given information, but it is important to take into account potential errors and factors that could affect the accuracy of the result. Further experimentation and verification may be necessary to confirm the amount of iron present in the vitamin.

## 1. How does absorbance help in finding the amount of iron?

Absorbance is a measure of how much light is absorbed by a substance. Iron has a specific absorbance value, meaning that it absorbs a specific amount of light at a specific wavelength. By measuring the absorbance of a sample containing iron, we can determine the concentration of iron in the sample.

## 2. What is the process for finding the amount of iron from absorbance?

The process involves creating a standard curve by measuring the absorbance of different known concentrations of iron. This curve is then used to determine the concentration of iron in an unknown sample by measuring its absorbance and comparing it to the standard curve.

## 3. What equipment is needed for this experiment?

The equipment needed includes a spectrophotometer, cuvettes, a light source, and solutions of known iron concentrations. It is also important to have proper safety gear, such as gloves and safety glasses, when working with chemicals.

## 4. What factors can affect the accuracy of the results?

There are several factors that can affect the accuracy of the results, such as the quality and purity of the iron solutions, the accuracy of the measurements, and any potential interference from other substances in the sample. It is important to carefully follow the procedure and use high-quality materials to minimize these factors.

## 5. Can this method be used for other elements besides iron?

Yes, this method can be used for other elements as well. However, the specific absorbance values and wavelengths will be different for each element, so a different standard curve will need to be created. It is important to research and use the appropriate method for each element being tested.

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