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Solubility question, please help

  1. Apr 8, 2006 #1
    It's driving me crazy that I can't figure this out. I've read the section in the book like 5 times and its not helping at all...argh.. Here it is:

    In which of the following aqueous solutions would you expect AgCl to have the highest solubility?

    pure water
    0.020 M BaCl2
    0.015 NaCl
    0.020 AgNO3
    0.020 KCl

    AgCl is generally insoluble in water so it can't be pure water. Ag is a metal ion, and my book says interaction with Lewis bases other than water can interact with the metal ion, and can dramatically affect the solubility of a metal salt like AgCl.The example they show in the book is AgCl(s) + 2NH3 ---> Ag(NH3)2 + Cl-.

    I am completely confused. I guess AgNO3 just as a random guess and its wrong. I'm thinking the answer is probably .02 M BaCl2 or .02 KCl because they both have a higher concentration than the remaining .015 NaCl answer, but I don't know which to choose or why one would be right and not the other.There is another section in my book that talks about precipitation and the separation of ions. The books says when Q < Ksp, sold dissolves until Q=ksp, but I don't know how that would help me when I can't figure out Q because I don't have the numbers. Could someone please help me understand this, I'm so confused... :surprised
     
  2. jcsd
  3. Apr 8, 2006 #2

    mrjeffy321

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    Science Advisor

    I think you are making the problem more complicated than it really is.

    Although we generally consider AgCl insoluble in water, that isnt exactly true. AgCl is slightly soluble in water, very, very slightly, so much so we usualy ignore it.

    In all 5 possible choices, we assume, water is the solvent we are using, even in the solutions containing other salt solutes.
    So which choice will most easily dissolve the AgCl?

    The common ion effect tells us that if the solution already has a "common ion" dissolved in it, it will make other salts with that ion less soluble.
    The two ions that AgCl will break up into would be Ag+ and Cl-. Out of the 5, 4 of the choices have common ions with AgCl (either the Silver+1 or the Chloride ion), thus we are left with pure water as the likely choice.
    This would make sense since pure water (in theory) would have nothing else dissolved in it, no other ions, nothing that would prevent the AgCl from dissolve [other than its already very low solubility].
     
  4. Apr 9, 2006 #3
    Thanks mrjeffy321, pure water did turn out to be the right answer. I see what I did wrong now (I definitely have a habit of making things harder than they should be, haha)..thanks again for your help
     
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