Supersaturated salt solution help, please.

August 23, 2011 1:46 PM

How do I make a 6M NaCl solution? It Won't Go Into Solution.

So, I've added the requisite 70.13g of NaCl into roughly 200 mL of ddH2O slowly and it worked for the majority of the salt. The last bit I tipped in after it had gone into solution just won't go! I've spun it on a slightly warm hotplate all night, it has come to a boil for at least 30-45 minutes (while spinning) and I'm at a loss. Clearly there has been some evaporation, so I'll be adding some more water but I have little hope that will work as I tried that earlier this morning.

Thoughts, anyone?

posted by oreonax to science & nature (6 answers total)

Add some water, let it dissolve, then boil the solution until excess water evaporates?
posted by m1dra3 at 1:53 PM on August 23, 2011

"roughly"? You're pretty close to the solubility limit. Theoretically, you should be able to get about 71 g into 200 mL at room temperature. But if you have less than 200 mL...

If it boiled, you lost some volume. But then you added some water?

You should probably figure out what volume you have.
posted by mr_roboto at 1:54 PM on August 23, 2011

I'm no expert on supersaturation, but it seems like you'll need to do something like what m1dra3 suggests. You're right at the solubility limit, so even with exactly 200mL of water you may need to raise the temperature in order to allow saturation to occur.
posted by lholladay at 2:06 PM on August 23, 2011

Yea, I remeasured it and added water to 200 mL, plus a little heat and we were done. * sigh * Thanks guys!
posted by oreonax at 2:13 PM on August 23, 2011

So what do you do with 6M NaCl solution? :-)
posted by bfu at 3:29 PM on August 23, 2011

bfu: "So what do you do with 6M NaCl solution?"

make crystals?
posted by ArgentCorvid at 6:21 PM on August 23, 2011