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Homework Help: Solubility in g/L of zinc hydroxide with pH of 8

  1. Jan 28, 2016 #1
    1. The problem statement, all variables and given/known data

    Zinc hydroxide has the chemical formula of Zn(OH)2. It has a very low solubility. What is the solubility in g/L of Zinc Hydroxide in a solution with a pH of 8?

    2. Relevant equations

    14-pH = pOH

    3. The attempt at a solution

    10^-6 (the pOH) gives me the concentration of the OH- ion.

    That gives me the unknown in mols/L.

    I multiply it by the molar mass, but it's wrong. What am I doing wrong?
  2. jcsd
  3. Jan 28, 2016 #2


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    Staff Emeritus
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    Homework Helper

    Why don't you show all your calculations?

    How many OH- radicals are there in each molecule of Zn(OH)2 ?
  4. Jan 29, 2016 #3


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    Staff: Mentor

    OH- in the solution are NOT from the dissolved Zn(OH)2.

    I would check what is the Ksp of the zinc hydroxide and use this number in the calculations.

    Sadly, the question is rather ambiguous. The final result is most likely different depending on whether the pH is buffered at 8, or is 8 initially (and there is no buffering effect). Hard to say what they mean.
  5. Jan 29, 2016 #4


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    I would read that as somehow maintained at pH 8 by some means, of which the most obvious is buffering (can also be done by e.g. An automatic titrator). Unfortunately you wil meet this sort of 'lab slang' often enough. But there is still not enough information and Ksp is needed.
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