Question

At 25 degrees c, 100 g of water will be saturated with 35.7 g of NaCl. Which word below describes the solution of 1.55 mol of NaCl dissolved in 250 ml of water?

Answer 1

I am pretty sure it's "saturated" since every 100 g of H20 needs 35.7 g NaCl to be "saturated". And .. if 250 mL= 250 g of H20, and 1.55 mol = 90.585 g NaCl... You are past the "saturation" point of 89.25 (since 89.25 = 35.7 x 2.5) ...

and if you agree that it's definitely not "unsaturated" how can we tell whether if it's just:
a. "saturated"
b. "supersaturated"
c. "metasaturated" (unlikely)

Thanks! :)

Answer 2

Probably supersaturated. It is just beyond saturated.

Answer 3

Really? How do you tell the difference though... like what value does it have to exceed (percentage?) for it go from plain saturated to supersaturated

Answer 4

If there's more than the saturation level, it's supersaturated, and unstable. If you provide some seeds, the excess solute will come out of solution.

Answer 5

Hmm... so after it hits 89.25 (the saturation point), it's supersaturated?

Answer 6

That's my understanding. And the only way you get past the saturation point is to heat the solution (so the saturation point is higher), dissolve the extra solute, then carefully cool the solution. Stir all you want with pure heart and righteous thoughts, but I don't think it will get anything more into solution beyond the saturation point :-)

Answer 7

lol .. "pure heart and righteous heart".. and thanks! I guess I will have to go with supersaturated now :)

Answer 8

righteous thoughts*

Answer 9

Well, maybe if you stir hard enough you'll warm the solution slightly, but... :-)

Answer 10

And then there's the heat transmitted through the walls of the vessel from the other hand holding on with a death grip as you stir madly :-)

Answer 11

lol maybe they should have us try that in chem lab instead of havin us do things we don't understand

Answer 12

@whpalmer and @preetha are slightly off on their descriptions of saturated vs. supersaturated. If you are trying to fit 90.5g of NaCl into 250mL of water, the water only "has room" for 89.25g. Any excess NaCl will sit at the bottom of the container. A trace amount may continue to dissolve, but will be offset by recrystallization somewhere else in the system. A flask that contains more solute than can fit into a solution is still saturated, when there's excess solute sitting on the bottom of the flask. Without more information, that's the most we can say.

If the question told you that there was no solid in the bottom of the flask, then the solution would be "supersaturated", holding more than it normally should. In order to do that, though, the solution has to be heated gently and is very unstable. The smallest additional seed crystal will force all that excess to crystallize instantly.

With such little information, the solution is "only" saturated, not supersaturated.

Answer 13

@JFraser I disagree. The problem statement says that it is dissolved.

Answer 14

Well, I talked to other people and they said it though "supersaturated" was the correct choice as well. Thanks yall for ur help! :D

Answer 15

@whpalmer4 you are correct, i got carried away in my explanation, thanks!