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Recrystallization of salts

  1. Aug 10, 2010 #1
    If I have a mixture of NaOH and NaNO3 and want to separate them via crystallization how would I go about it? Lets say my solvent is ethanol. 1g NaOH dissolves in 7.2ml ethanol whereas it takes 125ml to dissolve a gram of NaNO3. I'm not well versed in solutions, if I added a 72ml of ethanol to a 1:1 mixture weighing 20g would the ethanol dissolve mainly the NaOH since it has a far greater solubility?
  2. jcsd
  3. Aug 10, 2010 #2
    Well, yes, but there's technique involved, too. That depends mostly on what your starting material is and what you want to accomplish.

    Let's say that for some bizarre reason you took two 10g samples of the pure reagents and mixed them together - but the individual crystals were still pure. You could just add ethanol at room temperature and stir it up a while, and filter the result, and you'd have mostly NaNO3 crystals left on the filter. But frankly, both reagents are pretty cheap, and that's a lot of bother to get impure sodium nitrate, and you'd be better off tossing the mix down the drain and buying some more reagents.

    On the other hand, let's say you're after the evil bad guy (played by Gary Oldman) because he's going to do terrible things to your girlfriend (played by Angelina Jolie), but you can save her with some sodium nitrate (who knows why, it's Hollywood). Of course, you can't call Sargent-Welch for a delivery because their next secret evil lair delivery is next Tuesday, so you have to wing it. So you go into the secret evil bad guy lab, and you get his inexplicable mixture of sodium hydroxide and sodium nitrate. You put it in an erlenmeyer flask, and heat it up, and add boiling ethanol until it all dissolves. Then you take it off the heat and let it cool to room temperature. The sodium nitrate will drop out of solution as pretty crystals, and you filter off the liquid, and save the day. Gary Oldman gnashes his teeth, Angelina Jolie kisses you really hard, and then Brad Pitt shows up and punches you in the snoot for canoodling with his wife. So there you are. :-)
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