cnidocyte
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Competitive solubility
If I have a mixture of 2 salts weighing 6 grams, lets say Salt A has a solubility of 3g/mL while Salt B only has a solubility of 3mg/mL. If I add 3 mL
of the solvent would it become completely saturated with Salt A allowing me to filter out Salt B completely or would both salts get dissolved in the
solvent, just in a 1000:1 ratio?
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spirocycle
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do they share common ions?
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cnidocyte
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Yeah in the scenario that inspired me to start this thread they're both Na salts. NaOH and NaNO3 to be exact. I was pondering the idea of extracting
the NaOH with methanol since it has a way higher solubility than NaNO3. Its the NaNO3 I'm after though so I'm thinking about recrystallising if I can
get rid of a significant amount of the NaOH first.
[Edited on 9-1-2011 by cnidocyte]
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spirocycle
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I'm not familiar with the solubility products of the compounds in question, but if you could find them then it should be fairly straitforward to
figure it out.
KNaOH=[Na][OH] and [Na]=[OH] so KNaOH=[Na]^2
KNaNO3=[Na][NO3] and [Na]=[NO3] so KNaNO3=[Na]^2
so if sqrt([NaOH]>sqrt(KNaNO3), that is if the concentration of sodium ions from the NaOH exceeds the saturation point of the solubility product of
the NaNO3, then theoretically the NaNO3 with crystallize out (or not dissolve in the first place)
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ScienceSquirrel
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What is the ratio of sodium hydroxide to sodium nitrate?
If I had to separate them I would use the fact that sodium hydroxide is very soluble in alcohol while sodium nitrate is only slightly soluble.
http://en.wikipedia.org/wiki/Sodium_hydroxide
http://www.sciencelab.com/msds.php?msdsId=9927271
Add a measure of the mixture to methylated spirits, warm and stir, cool and then filter off the sodium nitrate. Wash with some more meths and then
dry.
The alcoholic sodium hydroxide could be used as a powerful grease busting drain cleaner! 
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cnidocyte
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Quote: Originally posted by ScienceSquirrel  |
Add a measure of the mixture to methylated spirits, warm and stir, cool and then filter off the sodium nitrate. Wash with some more meths and then
dry.
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Thats pretty much what I did but I used up all my methylated spirits and still was left with a large pile of undissolved solid so I decanted the
alcohol and allowed the solid to dry outside. It rained overnight though so the pyrex dish filled with water but even still theres a large pile of
undissolved solid. Lost my pH strips so I can't test the pH of this aqueous solution.
[Edited on 11-1-2011 by cnidocyte]
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ScienceSquirrel
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Are you sure that it is only sodium nitrate and sodium hydroxide in there?
They are both very soluble in water.
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dann2
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Hello,
The competitive solubility thing, more accurately described as mutual solubility can be read about that this link:
http://www.oxidizing.110mb.com/chlorate/mut_pdf.zip
It is not specific to your solids/liquids though.
Its not a terrible simple matter. What you want for to get things to happen easily if for one solid to be much more soluble that the other one
(obviously).
Try googling mutual solubility xxxxxx yyyyyyy
Dann2
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