Yup. V/V is for liquids; provided you're using them at about room temperature (to account for different coefficients of thermal expansion) it works really nicely. W/V is for solids-in-liquids, because measuring mass of solids is easy, but measuring volume of solids is hard (without immersing them!).
Of course, W/V isn't perfect for some solids anyway. For example, Magnesium Sulphate comes in two flavours; the anhydrate, and the heptahydrate. The difference in weight is substantial, so you have to know which hydration level you're being asked to solvate before W/V makes any sense. When I was coming up with a molarity-free protocol for TSS E.coli transformation, I hit this problem, and it was just fortunate that in that application there was a wide margin for error when it came to MgSO4 concentration, so I could give one weight for both types without issue.
On Wed, Jul 18, 2012 at 10:12 AM, Cathal Garvey <cathalgarvey@gmail.com> wrote:Wasn't this method created so it would be easier to make solutions,
> Although, I'd want to hit someone if they listed v/v for a
> crystalline/ground solid, because volume depends on granularity,
> hydration level, and any number of other variables. w/v is the norm for
> solids, thankfully.
>
etc? Volume of a solid is not easy to measure accurately unless you
got some special equipment, right?
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