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Homework Help: Solubility of Cr hydroxide in buffered solution

  1. Oct 1, 2007 #1
    1. The problem statement, all variables and given/known data
    What is the solubility (gram/liter) of Cr(OH)3 (103.02 g/mol) in a solution buffered at pH = 8.673? The pKsp of Cr(OH)3 is 30.220.

    2. Relevant equations
    Ksp = [Cr][OH]^3
    Cr(OH)3 -> Cr + 3OH

    3. The attempt at a solution
    I have already solved that Ksp = 6.0256 E -31, but i'm not entirely sure what to do with the buffer pH. I tried using it to find the pOH and subsequently [OH], but for some reason I'm not getting the right answer. Do I plug [OH] into the Ksp equation after finding out the concentration using the pH or is there a step i'm missing?
  2. jcsd
  3. Oct 2, 2007 #2


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    Science Advisor
    Homework Helper
    Gold Member

    Sounds like you are approaching it correctly. Use the concentration of [OH-] you obtain from the pOH in the Ksp expression and determine [Cr+3]. From that revelation back out how many grams of Cr(OH)3 will produce that concentration of [Cr+3].
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