[Vezz]

I couldn't find a topic quite like mine when I used the search function, but if there is a post about this already, you can just redirect me there.

A Pre-Lab question for my upcoming Iron Titration Lab is:
Using data generated by following the procedure in the lab, you calculate that there is 3.315 x 10^-5 mol of Fe²⁺ in an average 10.00 mL sample of your stock solution. Calculate how many mg of Fe²⁺ were present in a single tablet.  Note that you initially dissolved two tablets to make the 100.0 mL of stock solution.


We went over this type of calculation in class, the example we used was:
Molecular Weight: 278 FeSO₄7H₂O/mol
1 mole Fe²⁺ =  1 mole FeSO₄7H₂O

If there are 2.40x10^-4 mol Fe²⁺ we calculated that there are 334mg FeSO₄7H₂O/tablet:

(2.40x10^-4 mol Fe²⁺ / 10mL) * (100.0mL / 2 Tablets) * (1m FeSO₄7H₂O / 1m Fe²⁺) * (278.0g  FeSO₄7H₂O / 1m FeSO₄7H₂O) * (1000mg / 1g) = 334mg FeSO₄7H₂O / Tablet


I used this example, given by my professor, to find the Pre-Lab calculation:

(3.315 x 10^-5 mol Fe²⁺ / 10mL) * (100.0mL / 2 Tablets) * (1m FeSO₄7H₂O / 1m Fe²⁺) * (278.0g  FeSO₄7H₂O / 1m FeSO₄7H₂O) * (1000mg / 1g) = 46.1mg FeSO₄7H₂O / Tablet

The available answers are:
18.51 mg
7.448 mg
10.92 mg
0.9256 mg
8.422 mg
9.256 mg
8.711 mg

I don't really know what I am doing wrong, so thank you for the help.

[ARGOS++]

Dear vezz;

In case your method-description holds for both analyses, then you can make the proof:
  2.40 * 10^-4  :  334mg/Tbl.   =   3.315 * 10^-5  :   x mg/Tbl.
  ====>  x mg/Tbl. = 334 mg/Tbl. /  (2.40 * 10^-4)  * (3.315 * 10^-5) = 46.13 mg/Tbl.

This will tell you, that your calculation is correct!

Good Luck!
                    ARGOS⁺⁺

[Vezz]

So, I didn't read the directions clearly, and solved for the mass of the tablet, not the mass of the Iron.

(3.315 x 10-5 mol Fe²⁺ / 10mL) * (100.0mL / 2 Tablets) * (55g Fe²⁺ / 1 mol Fe²⁺) * (1000mg / 1g) = 9.11625\

Thank you for the response!

[ARGOS++]

Dear Vezz;

I got for x of Fe²⁺ = 9.257 mg/Tbl. (Check the MW of Fe!).
But the method is now correct.

Good Luck!
                    ARGOS⁺⁺