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Finding concentration of a sample

  1. Apr 23, 2016 #1
    1. The problem statement, all variables and given/known data
    1.02 grams of an unknown sample, that contains iron and some other things. Amount of iron is unknown, other substances are unknown.

    The concentration is 0.023 mg Fe/mL

    The question says find the mass of Fe (in mg) in the 1.02 gram sample.

    Exact question is:
    "The unknown iron solution in the 25 mL volumetric flask was the result of pipeting 3.00 mL from the 1000.00 mL flask which originally contained the entire dissolved sample. Use principles of dilution and concentration to find the mass in milligrams of iron present in the 1.00 liter volumetric flask. This is the amount present in the original dry sample."

    The concentration i gave was for the 25 mL

    2. Relevant equations

    none.

    3. The attempt at a solution

    I'm guessing i have to convert from the concentration, to molarity, and go to grams divide by molar mass, something like that. I think it will be something similar to that. I will update the attempt because its not really clear right now.
     
    Last edited: Apr 23, 2016
  2. jcsd
  3. Apr 23, 2016 #2

    mfb

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    Staff: Mentor

    ml of what? Is the substance dissolved somewhere? If it is a solid, you still need the density or something similar you use that value.
     
  4. Apr 23, 2016 #3
    These are the exact directions. I seriously have no idea how to do this. We weren't taught this.

    "The unknown iron solution in the 25 mL volumetric flask was the result of pipeting 3.00 mL from the 1000.00 mL flask which originally contained the entire dissolved sample. Use principles of dilution and concentration to find the mass in milligrams of iron present in the 1.00 liter volumetric flask. This is the amount present in the original dry sample."

    The concentration i gave was for the 25 mL
     
  5. Apr 23, 2016 #4

    mfb

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    Why didn't you include that part in the original version of the first post? The question does not make sense without that part.

    If you have 25 ml of 0.023 mg Fe/ml, how much iron do you have in that 25 ml?
     
  6. Apr 23, 2016 #5
    It sounds like he only has 3ml in the the flask that can hold 25ml.

    Where did you get the concentration and 1.02grams from? It's not it the "exact question".

    But if the concentration is correct then just multiply it with the ml of solution in the 1L flask. By the way you don't say how much solution there is in the 1L flask.

    I don't think your teacher was giving you a trick question here but if you give us all the information in the question we can help you out.
     
  7. Apr 24, 2016 #6

    mfb

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    Staff: Mentor

    Where would be the point of the 25 ml thing then? There would also be no reason to take 3 ml, and the reference to dilution would not make sense.

    I'm quite sure the 3 ml get diluted in the 25 ml flask.
     
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