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Chem. Ksp and precipitation

  1. May 9, 2009 #1
    1. The problem statement, all variables and given/known data
    NaCl is added slowly to a solution that is 0.010M in each Cu+, Ag+ and Au+. Ksp's are 1.9x10^-7, 1.8x10^-10 and 2.0x10^-13 respectively. Which compound will precipitate first?


    Can anyone tell me how the Ksp is different from Ka? and the relationship to precipitation?
     
  2. jcsd
  3. May 10, 2009 #2
    k is just a concentration constant, sp= solubility, a = acid. same concept, different setups, however. ksp only cares about the products.


    I'm guessing Ag+ precipitates first, because AgCl is insoluble. the rest are. (I'm not 100% sure, however.)

    But if we assumed they were all soluble...
    ksp = [.1][Cl-]

    substitute stuff into that equation.
    the one that gives the lowest concentration of Cl- precipitates first
     
  4. May 10, 2009 #3

    Borek

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    Staff: Mentor

    Google solubility product.
     
  5. May 10, 2009 #4

    Borek

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    Staff: Mentor

    To some extent yes, but there are important differences. You can't use Ka to decide if the new phase emerges, you can use Ksp for that. Reaction quotient for acid solution always equals Ka, reaction quotient for solution containing weakly soluble salt doesn't have to.
     
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