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Homework Help: Solution concentration and ppm

  1. Oct 20, 2007 #1
    Hi all, I have 2 short questions, that have caused me trouble in my study.

    What is generally considered to be a highly concentrated solution?
    eg. 250mL acid in 10L water.
    This is 250E-3/10 = 0.25/10 = 0.025 M.
    Would that be considered a concentrated solution? as it seems very low ...

    In a sample of ground water, iron in the form of Fe2+ was found to have concentration 9.00E-3 M. Assuming the density of water is 1.00 gmL-1, what is the concentration of Fe2+ in ppm?
    Now I'm not really sure what is going on here, but given the Fe2+ has a molar concentration of 9.00E-3, surely there is a way to convert that to gL-1 and then to mg/kg (ppm solute/solvent form)?
    am i correct?
    (just need to be lead on the right track there ...)

  2. jcsd
  3. Oct 20, 2007 #2


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    Hey :smile:

    To calculate the molarity of the final solution, youre going to need to know what the concentration of the original 250mL acid solution is, so you can find how many moles in the final solution.
  4. Oct 20, 2007 #3
    Hey sup

    The question for the first part im working on doesnt actually state any other values for me to work with. It states; "Household vinegar can be produced by adding 250mL of acetic acid to 10L of pure water. Which of the following best describes the acetic acid".
    The answer is; "a concentrated solution of weak acid"
    Now what I worked out before (0.025M) I thought was pretty low for a high concentration.
    Any ideas?
  5. Oct 20, 2007 #4
    part a i got fine now... just another stupid misunderstanding ....

    any other suggestions for part b?
  6. Oct 20, 2007 #5


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    For the second question, you are told the concentration of Fe+2 in mol/L. You should start by converting that to a concentration in g/L, and then g/mL. See if you can go from there.
  7. Oct 20, 2007 #6
    Thanks for your help :)

    =0.50265 g/L
    =0.50265 x 10^3 mg/L
    =502.65 mg/L
    502.65 ppm

  8. Oct 22, 2007 #7


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    The acetic acid referred to in the question is the glacial acetic acid used to make the more dilute vinegar (250 mL in 10L). It is essentially 100% acetic acid. Thus the 'concentrated solution of a weak acid" is the closest to the correct answer, however; it isn't really a solution at all since it is water-free. It's a pure compound.
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