Actually, that is not what I am saying at all. % by volume is a legitimate way of expressing concentration, but g/L is not the same as % by volume.mnstrviola wrote:Flavorflav wrote:It isn't, I did the math wrong - it is really 6.2%. When you say %, you pretty much always mean % by mass. 65 grams is 6.5% of 1000 g, so the amount of water you should add is 1000-65 = 935 g. If you use their method, you end up with a solution of density of about 1.047 (obtained from here), so your liter of solution masses 1047 grams, of which 65 is salt. 65/1047= 6.2%.
Okay so you are saying that % concentration is based on mass, not volume.
mnstrviola wrote: Doing some research on this, I believe that there are multiple ways to express % concentration.
http://chemistry.about.com/od/lectureno ... ration.htm
http://pages.towson.edu/ladon/concas.html
So I guess both methods are okay. However, for the national competition, they will want you to use the method with x grams in 100mL = x%.
Again, correct me if I'm wrong.
No, there are multiple was of expressing concentration. There are only two ways of expressing % concentration, % by mass and % by volume. The latter is only used for solutions involving two liquids, so that leaves one method of expressing % concentration when the solute is a solid, % by mass. As I said before g/L is a perfectly legitimate way to express concentration, but it is not % concentration.