SV: Glycerol: v/v or w/v?
Wolfgang.Schechinger at med.uni-tuebingen.de
Fri Feb 25 16:54:08 EST 2000
UUUh. Actually, I just wanted to clearify that one should indicate
if one prepares the mixture w/v or v/v.
And the experiment (one of the *few* -no flames please- I like in
physical chemistry) I cited only should illustrate what could go
wrong. Problably not when making 50 % (x/v) glycerol for any purpose,
but e.g when mixing solvents for chromatography. (For one mixture, 3
people in my lab were performing the protocol in three different
ways...I omit the rest of the story here.)
Have a nice weekened!
> From: "Dag Rune" <dag.rune.gjellesvik at biotec.as>
> Subject: SV: Glycerol: v/v or w/v?
> Date: Fri, 25 Feb 2000 16:08:06 +0100
> Organization: Telenor Online Public Access
> To: methods at hgmp.mrc.ac.uk
> "Wolfgang Schechinger" <Wolfgang.Schechinger at med.uni-tuebingen.de>
> skrev i
> meldingsnyheter:200002242258.XAA20280 at intwww.zit.med.uni-tuebingen.d
> e... > No. Not obviously. I use w/v. Did you ever try to pipet 100%
> > glycerol? For this reason, one always should how the dilution was
> > performed. > In real life, it normally should not matter. What
> matters more is, > that there is a difference if you have 50 ml of
> glycerol and add > water q.s. 100 ml or if you have 50 ml of water
> and add glycerol q.s. > 100 ml. For understanding this phenomenon,
> mix 50 ml of ethanol > **and** 50 ml of water in a graded cylinder
> (the experiment is easier > to perform with EtOH). > > Enjoy! > >
> This is a discussion that calls for pedants - to be boringly
> accurate, you may weigh in 1.26 g glycerol per ml water. This gives
> you a 50% v/v solution. And now to the volume change: to find the
> **new** volume, you divide the weight by 1.14 (not 1.13) to get the
> correct volume. We actually measured the density of 50% v/v glycerol
> once. These things may not matter at all when you consider the
> temperature. I would think that the volume change of water is quite
> different from that of glycerol with changing temperatures.
> Dag Rune
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Dr. Wolfgang Schechinger, Dept. of Pathobiochemistry
University of Tuebingen, Germany
email: wolfgang.schechinger at med.uni-tuebingen.de
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