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Homework Help: Can't seem to match the answer! help!

  1. Apr 26, 2005 #1
    What is the concentration of Sr(OH)2 in a solution with a pH of 11?

    The answer is SUPPOSED to be 5.0 x 10^-4...buuut i keep getting 0.001..
    i didnt think this would be a complicated question.. all i did was found the pOH to be 3..and found the concentration of OH, giving me .001
    what am i doing wrong?:S
  2. jcsd
  3. Apr 26, 2005 #2
    I'm not completely sure (I should be sure though! :P)

    Equation is:

    Sr(OH)2 + H2O <==> 2OH- + Sr((OH)O <---??

    But anyways, the important thing is that there the hydroxide anion has a subscript of 2. You have to pay attention to the stoichiometric rations; therefore the molar ratio of the concentration of Sr(OH)2 to OH is 1:2.

    Your 0.001 concentration of OH- present in solution is correct, but then you have to divide it to two to get the concentration of the Sr(OH)2.

    [tex]0.001 \div 2 = 0.0005 or 5.0 \times 10^{-4}[/tex]

    Last edited: Apr 26, 2005
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