[K2054]

- (Conc.=0.0250g/L) iron vitamin tablet in 40mL of water, dissolving.
- tranferring to a 100mL flask and diluting up to 100mL.
- measured absorbance of vitamin solution at 508nm, that resulted in 0.15.
- A graph was made and after dropping a vertical line from the absorbance value down to the concentration
- corresponding concentration on graph was 0.0006g/L?

im not sure if thats right.... because the final mass after all the calculations is way off the 10mg advertised mass of the iron in the tablet.

1) calculate the concentration of iron (g/ml) in the 100mL volumetric flask which contains the solutin in which the vitamin was originally dissolved?
2) using the concentration and volume of the flask calculate the mass of iron present in the vitamin tablet?
3) convert the weight to milligrams?

what i did:

1) (0.0006g/L)(40mL)=C2(100mL)
which gives:
0.00024g/L x 1L/1000mL = 0.00000024g/ml

2) 0.00000024g/mL x 100mL = 0.000024g

3) 0.000024g x 1000 = 0.024mg?


**** Concentrations of the standards for the graph were found like this, messed up here maybe?
(25mL is the flask that the standard was diluted in)
(1mL, 2mL, 3mL, 4mL are the amounts of iron put in each flask)
(0.0250g/L is the concentration of the iron)

(0.0250g/L)(1mL)= c2(25mL)
=0.001g/L

(0.0250g/L)(2mL)= c2(25mL)
=0.002g/L

(0.0250g/L)(2mL)=c2(25mL)
=0.003g/L

(0.0250g/L)(2mL)=c2(25mL)
=0.004g/L

[Borek]

1) (0.0006g/L)(40mL)=C2(100mL)

Your description of th eexperiment is rather ambiguous, but judging from what you wrote above, 0.0006 g/L was in the 100 mL, not in the 40 mL.

Not that it changes the final result by orders of magnitude.

[K2054]

Your description of th eexperiment is rather ambiguous, but judging from what you wrote above, 0.0006 g/L was in the 100 mL, not in the 40 mL.

Yeah, the iron vitamin was only dissolved originally in 40 mL of distilled water. So that should be the initial volume in the dilution formula?

The actual dilution itself took place in a 100ml flask, so the 40mL dissolved iron vitamin solution was diluted up to 100mL.

[K2054]

If the dilution formula isn't where the problem was.. then maybe it's in the concentration of iron calculations for the graph?

How would you go about calculating that? I did it like this..

The concentration of the iron solution is 0.0250g/L, and it was added to five 25mL flasks in the increments as follows:

1ml in one flask, 2ml in one flask, 3ml in one flask, and 4ml in one flask? 

(0.0250g/L)(1mL)=(C2)(25mL)
= 0.001g/L?

[Borek]

Concentration calculations (for the calibration curve) look OK, but nobody can judge your result without knowing what you measured.

You may assume tablet was just dissolved in 100 mL, no need to calculate dilution - 40 mL is measured only approximately, it is filling up to 100 mL that needs to be precise.

[K2054]

You may assume tablet was just dissolved in 100 mL, no need to calculate dilution - 40 mL is measured only approximately, it is filling up to 100 mL that needs to be precise.

Thank you so so much! that helped me a lot, i think i have it now