Stock Concentration of Solvents - (Feb/14/2007 )
I am having an issue determining what my stock concentration of two solvents that I need to dilute for HPLC. I've got 1-Butanol and Acetone. I need to make 100 mM solutions of each to use as standards on an HPLC run with some samples.
My problem is that for the life of me (and some other lab mates) i cannot figure out what molar concentration the stock is in. The chemicals are direct from Fisher, and I've looked up the MSDS files on them, but the closest information I've gotten is that it's 99.9% pure and the formula weight. Is there anything I'm missing or do I just assume the stock chemicals from the company are 1M? Once I know the stock concentration, my problem is solved.
Thanks for any and all help.
To make a 1M solution of each
you need either know
the specific gravity, ie the density of said solutions. and a good meassuring cylinder
a good scale and pipette (This option is the easiest)
Normally 99.9%, means that out of 1000g of each solution you will 999g of your desired subtance and 1g of somekind of impurity.
Though you might have to beware as some companies say 99.9% pure when they actually mean that if you were vapourise a sample of the said compound, 99.9% of all volatile molecules are your desired chemical and 0.1% is contaminant. Of course any bit of solid junk that can not vaporise is not considered in the above calculation of 99.9% purity. This bit of impurity can be quite significant.
Now a 1M solution of X means.. that within a 1L solution there is 1mol of solute X.
So to calculate a 1M solution,
first determine how many mols are required. To make things easy I assume 1L of solution is required. Ie 1mol
Now find out how much does 1mol of 1-butanol /acetone weights
Place a 1L measuring cylinder on a scale. Tear/zero the scale. Now fill the measuring cylinder with 1-butanol/acetone until the desired weight is measure out. Once done, top up the measuring cylinder with sterile distilled water until the 1L mark is reached.
You will realise that a pure solution of acetone / 1-butanol probably has a molarity greater then 1. Much like the pH of concentrated sulphuric acid is 0. And there are a class of super acids with negative pH values.
Pure acetone density: 0.7860 g/mL, that gives 13.53 M. 73.9mL for one mole.