What does 2 vol (w/v) mean?

I came across a protocol saying:



> 
> Homogenize 50 g powdered plant material (accurately weighed and recorded) in 2
>  vol (w/v) acidified methanol.
> 
> 
> 


What does **2 vol (w/v)** mean?




Weight per volume percent. It's basically the density. 


$$ w/v = \frac{mass\_{solute}}{volume\_{solution}} \* 100 $$


Usually it includes units too, but you didn't specify. I'm guessing it means grams per liter?


For more, see <http://www.ausetute.com.au/wtvol.html>


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It is actually a poor protocol telling you that the mass of your solute (or disperded material) should go in a double volumetric amount of liquid. Strictly speaking you do not have the knowledge of what you are supposed to do, as units are missing. I am experienced in lab and personally I wouldn't be able to interpret the protocol without guessing, and I'll use 50 times 2 = 100 millilitres of solvent.


As additional comment, the w/v concentration should be used with caution as it is susceptible of being practically meaningless (volume contraction / dilation upon solution preparation) without further knowledge. Also, if the attained solution has to be used as a source of solute, its density must be known (unless it is aqueous and very diluted). 


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