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

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Discussion Overview

The discussion revolves around the preparation of a 100 mg/ml solution of glacial acetic acid in methanol, focusing on the methods of measurement and dilution. It includes considerations of density and the challenges of weighing small amounts of liquid accurately.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant inquires about the correct method to prepare the solution, specifically questioning the weighing and dilution process.
  • Another participant suggests measuring the acetic acid with a pipet and preparing the solution in a volumetric flask.
  • A participant confirms their understanding of weighing 100 mg of acetic acid and diluting it to 1 ml with methanol, while also asking about scaling up the preparation for larger volumes.
  • One response emphasizes the difficulty of weighing small amounts accurately and recommends using volume measurements instead, leveraging the known density of glacial acetic acid for calculations.
  • Another participant proposes preparing larger volumes to avoid issues with weighing small quantities and raises concerns about the accuracy of volumetric methods due to potential temperature variations affecting density.

Areas of Agreement / Disagreement

Participants express differing views on the best method for preparing the solution, particularly regarding the use of weight versus volume measurements. There is no consensus on the optimal approach, and the discussion remains unresolved.

Contextual Notes

Participants note the importance of considering the density of glacial acetic acid at different temperatures, which may affect the accuracy of the solution preparation. There are also unresolved questions about how to calculate the necessary volume for very small concentrations.

Who May Find This Useful

This discussion may be useful for individuals involved in chemistry or laboratory work, particularly those preparing solutions and dealing with measurements of liquids.

ChemiePham
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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.
 
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Measure the acetic acid with a pipet and prepare the solution in a volumetric flask.
 
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?
 
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.
 
ChemiePham said:
Now what happens if the desired concentration is just too small to weigh out...How would you calculate the volume needed arithmetically?

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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