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Seperating with solubility

  1. Apr 27, 2005 #1
    Can you seperate soluble compounds by changing the concentration? Are some soluble compounds more soluble than others? If you had a nitrate (KNO3, NaNO3, etc) and another less soluble compound in a 1.0M solution in water and you added more and more nitrate compound would the less soluble compound start leaving solution ,get pushed out by the nitrate so to speak, and form a solid precipitate?

    Thank you,

  2. jcsd
  3. Apr 27, 2005 #2
    Ain't sure...
    But yes.

    Have you come across the Solubility Constant (Ksp)?

    Ksp's of soluble compounds tell you what concentration will dissociate (and thus what concentration will remain as a precipitate)

    If the Ksp's of the 2 compounds are different AND they share a common ion, then by adding that common ion you can precipitate the less soluble compound. The extent to which you can do this depends on how much of both compounds you've added and how differnt their Ksp's are.

    And although it may be possible to force an unrelated compound out of solution, it's more efficient to use something with a common ion.
  4. Apr 28, 2005 #3


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    If the two compounds have any of the same ionic components, then we're talking about the common ion effect.

    Note that all compounds have a saturation state in water and furthermore a supersaturation state.

    Assuming an very large excess of water, the two compounds will not interact appreciably for any changes in solubility. If someone knows of a specific, interesting dynamic, let me know.
  5. Apr 28, 2005 #4

    Wouldnt the only way to get the common ion be two add one of the compounds sharing the same common ion? If you had CaNO3 and NaNO3 in a solutin and you added more CaNO3, wouldnt you push the NaNO3 out of solution even if NaNO3 is more soluble?
  6. Apr 28, 2005 #5


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    No, calcium nitrate will precipitate first.
  7. Apr 29, 2005 #6


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  8. Apr 29, 2005 #7


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    It's clear that if you add CaN03 to a solution containing NaN03 and the former is less soluble than the latter, the solution will become saturated quickly with respect to CaN03. The CaN03 will simply not dissolve further, since the solution is supersaturated; it will not dissociate to Ca2+ and N032-.

    got it?
  9. Apr 29, 2005 #8

    oh, yes that makes more sense now that I think about it. Can you link me to a chart of compounds and their Ksp?
    Last edited: Apr 29, 2005
  10. Apr 29, 2005 #9


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