[h999ds]

Hey guys


I have a known substance with a MW of 625. It is in a 50ml bottle that says it is in 10% aqeuous solution.

How am i supposed to know/calculate its concentration in M?

[sjb]

What measure of % are you using? w/w / v/v .. ?

[h999ds]

volume

[wpenrose]

Bad question. Percentage alone isn't sufficient for a concentration unit.

In general, solids dissolved in liquids are expressed as grams per 100 milliliters of final solution (called wt/vol or w/v)

Liquids in liquids are usually milliliters per 100 mL of final solution (v/v), but other folks will us grams per 100 mL.

There are lots of exceptions. Yet other people will say grams per 100 mL *solvent*, or mL per 100 mL solvent.  Go figure. That's why you can't rely on percent concentrations unless the conditions are specified.

Dangerous Bill

[h999ds]

yes i am 100% confused with you.

here is the product:
http://www.emdbiosciences.com/Products/pds.asp?catno=648463

here is a tool i found on wiki:
http://www.etoolsage.com/converter/consistency.asp?toolsort=1500


i seem to be able to fill in all of those numbers when selecting v/v, and there is an output of a certain M, but my question is how can i do this on pen/paper?

[wpenrose]

It's a 10% solution, and you can assume the errors in both concentration and molecular weight could be as high as +/-10%, since it's a sticky polymer.

The nature of the detergent suggests it's a liquid, but it likely has a density near 1, so it won't matter much. You can assume that 10 mL of the solution contains 1 gram of the compound. The rest should be easy.

DB

[Borek]

Bad question. Percentage alone isn't sufficient for a concentration unit.

Yes it is

w/w for any mixture is unambiguous.

[wpenrose]

w/w can be weight per final wt of solution or wt per wt of solvent. I've seen both.

Rarely does it matter  Percent was never meant to be more than approximate. In this particular problem, a commercial polymer solution, I'd be surprised to see the MW error less than  +/- 100, or the concentration error less than +/- 0.5%

DB