Salting Out didn't work!

[bbry...@gmail.com]

We tried the salting out procedure for isopropanol and it completely bombed. We were using 70% IPA, lots of water, and not very much salt- as instructed by the lab manual. We tried adding more salt and less water, and got the same result. I did some reading online and found that the procedure is used to dehydrate isopropanol, so I used a suggested procedure that called for isopropanol and salt only (lots of salt!) I also tried coloring the isopropanol with a Sharpie pen, something I saw in another post. I got an immediate separation that was very clear with the colored alcohol.

So why didn't it work the first time? Is the line of separation very hard to see? Did I not use enough salt? Too much water?

[The Home Scientist]

We suggested adding water for two reasons: first, some people might use 99% isopropanol, which would leave them without any water to separate. Second, we wanted to establish that salting out is effective even for dilute solutions of isopropanol. The instructions in the manual should yield a good separation, with anything from about a 1 to 1.5 mL layer of isopropanol. As long as there's salt visible in the bottom of the tube, there's enough in there to saturate the water later and allow the dehydrated isopropanol layer to separate. I'm sure your original separation worked properly. Yes, the layers are difficult to discriminate visually because both liquids are colorless. Using a dye that's preferentially soluble in one or the other liquid is one way to visualize the separation. Another way is to use the different indices of refraction of the two liquids by dipping a glass stirring rod into the tube. At the boundary, the glass stirring rod will appear to be sheared because of the different refractive indices of the liquids.