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Prepare a 100mg/ml solution of glacial acetic acid in methanol

  1. Oct 23, 2009 #1
    How to prepare a 100mg/ml solution of glacial acetic acid in methanol? The density of glacial acetic acid is 1.05 g/cm^3.
     
  2. jcsd
  3. Oct 23, 2009 #2

    symbolipoint

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    Measure the acetic acid with a pipet and prepare the solution in a volumetric flask.
     
  4. Oct 25, 2009 #3
    OK, so let me see if I understand you correctly.

    Because my acetic acid is a liquid, I would weigh out (on a scale) 100 mg of acetic acid into a volumetric flask and then dilute to 1 ml with methanol. Is this correct?

    And if I had to prepare 10 ml having a concentration of 100 mg/ml, I would just multiply whatever it was that I weighed out for the 1 ml solution by 10, right?

    Now what happens if the desired concentration is just too small to weigh out...How would you calculate the volume needed arithmetically?
     
  5. Oct 26, 2009 #4

    symbolipoint

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    You would have too much trouble weighing the precise amount of acetic acid that you would want. Use VOLUME with a pipet. You have the density of your acetic acid, so just calculate how much volume you need for the amount of final solution that you want.

    You may think in this way:
    Find how much volume acetic acid needed for 1 ml.
    Now, how much volume acetic acid do you need for your target ml. of final solution?
    In other words, how much larger is your target solution than 1 ml? This is how many times more acetic acid material you need to pipet.
     
  6. Oct 27, 2009 #5

    chemisttree

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    The way you do this is to make up more than 1 mL at a time. Instead of weighing out 100 mg and diluting to 1 mL, why don't you try to weigh out ten times that amount and dilute it to 10 mL? Or 100 times that amount and dilute it to 100 mL?

    And... don't do it volumetrically if you want an accurate solution. Density is given for one temperature (probably 25C) and you may be working at a different temp. Do you know how density changes with temperature for this compound? Not likely.
     
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