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Homework Help: Analytical chem lab and dilution factors

  1. Nov 21, 2008 #1
    1. The problem statement, all variables and given/known data
    Find the mg of Fe in vitamin pill. Vitamin pill was dissolved in 25mL HCl which was then diluted to 250mL with water in flask. 25mL of that solution was then diluted to 100mL in another flask. 10mL of the second was diluted to 100mL in another flask. Absorbance of the last solution and standard solutions were taken and a calibration curve created. It was determined that the sample solution contained 12.0mg/L iron. Determine the number of mg of Fe in tablet.

    2. Relevant equations

    3. The attempt at a solution

    12.0mg/L x 0.100L x (100mL/25mL) x (100mL/10mL)=48.0mg Fe in tablet

    I am not sure if I am correct. Do I need to account for the 25mL HCl diluted to 250mL as well?

    Any help in direction would be greatly appreciated! Thanks.
  2. jcsd
  3. Nov 21, 2008 #2


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    25 mL (whole sample) ---> 250 mL Stock solution A

    Stock solution A (25 mL) -----> 100 mL Stock solution B (1/4 as strong as A)

    Stock solution B (10 mL) -----> 100 mL Sample solution (1/10 as strong as B)

    Can you get there from here?
    (your answer is not correct)
  4. Nov 21, 2008 #3
    chemisttree: So, the original solution is 40x stronger than the sample solution. So if the sample solution contains 12.0 mg/L and total volume pipetted was 10 mL , is this the iron content of the tablet?

    12.0 mg/L x 40 = 480 mg/L x 0.010L = 4.8 mg

    Is this correct?

  5. Nov 24, 2008 #4


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    Not yet!

    Here is where you went wrong with your logic...
    Why is it important to know how much was pipetted from Stock solution B to the final Sample solution? You already used that information to determine that the Sample solution is 1/40 th as strong as the original solution which has the tablet's entire contents.
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