[Phamie]

How do I prepare a 100mg/ml solution of glacial acetic acid in methanol?

Do I first calculate the Molarity of acetic acid since I have the FW and density and then from Molarity, convert that to mg/ml???

[Borek]

You don't need molarity. Calculate how many grams of acetic acid you need for a volume of solution that you are preparing, measure this amount (either using scale or calculating what volume you need and measuring volume), than fill up with methanol.

[Phamie]

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?

[Borek]

You are on the right track, although you may have problems finding volumetric flasks of 1 & 10 mL volumes. You will be probably forced to prepare some larger volume - like 25 mL.

Instead of weighting you can measure volume - but you have to check what volume need. That means finding density of the glacial acetic acid and using it. Note, that it is much easier to measure appropriate volume (we are talking about volumes below 1 mL) with pipette, than to weight 100 mg.

[Phamie]

OK, so density of acetic acid is 1.049 g/cm^3 = 1.049 g/mL

So to make a 10 ml solution having a concentration of 100 mg/ml my calculation would be as foolows:

100 mg/ml x 1049 mg/ml x 10 ml = 0.953 ml

is this right?

[Borek]

Wrong as written, correct as calculated