5 M NaCl stock - (Oct/29/2012 )

Hi guys,

I was trying to make a 5 M NaCl stock but I have problems to dissolve it.

I added 292.2 g to about 750 mL MQ initially but after 2 hours didn't dissolve so I added more water and heat it up. I even reach to boiling to dissolve but did't work either. Even worse, the solution surface started to cristalize ¬¬'...
It's the first time I have to prepare this stock and I'm a little bit paranoid already , maybe the balance I used does not work properly or the bottle had another chemical ?

I don't know, having a problem with this and not with other really complex solutions pfff

If anybody has any suggestion trick or whatever, it would be good

The solubility of NaCl in H20 is about 360 g/l - you have 750 ml of water (therefore 360*0.75=270) and 292 g...add some more water.

I added more than the expected and it didn't dissolve overnight

I would try re-weighing the NaCl. It does tend to crystallize at the surface - keep it covered with parafilm. I can't recall ever having it not dissolve, so I'm not much help unfortunately.

Do you need 5 M exactly or should it just be a saturated NaCl solution? If it's the latter case, then some precipitation is part of it (it's an equilibrium of precipitation and dissolving again...)
And add the NaCl slowly and not all at once...

I found autoclaving helps with dissolution with even just 500ml 5M NaCl solution

What was your final decision on this issue. I have also found the same issue.