March 27, 2017

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Calculate mass of iron in tablet by spectroscopy?

I have to calculate the mass of iron in a tablet..The manufacturers claim it contains 60 mg elemental iron.
background info: The tablet was crushed and dissolved in 25ml of 6M Hcl, filtered and added to a 100ml volumetric flask where it was diluted to the 100 ml mark with distilled water (step 1). 5mL of this solution was taken out and added to a second volumetric flask( reagents necessary were also added) and the sample was diluted to the 100ml mark (step 2)

10 ml of this second solution was taken and added to yet another flask and it was diluted up to the 100 mark with distilled water. The abosrbance of this solution was 0.170

From my plot, of absorbance versus concentration for the standard solutions the gradient (e) was 0.1842 which is my molar absortivity coefficient.
The mass of the tablet used was 0.2084g

I have to calculate the mass of elemental iron in this tablet.

This is what i have so far:
since A=elc
then c= a/el
= 0.170/0.1842 x 1 = 0.923 micro grams of fe/ml
since this was a 10 ml portion of the second solution which had a vol of 100 ml
then i found how much was originally in the second solution
which gave me a concentration of 9.23 micrograms fe/ml.. this is where i am stuck

How do i find how much iron was in the 5 ml (step 2) i took out since a dilution took place andhow do i determine how much iron was in the ORIGINAL solution in step 1.
Thanks alot

  • Chemistry - ,

    If we take the last number you have of 9.23 ug Fe/mL, that is in the second 100 mL flask. What went into that, That was 5 mL up to a 100 so 20 x 9.23 should give the concn in the original flask.
    9.23ug Fe/mL x (100/5) = ? ug Fe/mL in the original. Than ?ug Fe/mL x 100 mL will give the total ug Fe in the sample of 0.2084g

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