SV: Glycerol: v/v or w/v?

Dag Rune dag.rune.gjellesvik at biotec.as
Fri Feb 25 10:08:06 EST 2000


"Wolfgang Schechinger" <Wolfgang.Schechinger at med.uni-tuebingen.de> skrev i
meldingsnyheter:200002242258.XAA20280 at intwww.zit.med.uni-tuebingen.de...
> 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!
>
> Wolfgang

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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