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Two pH questions i don't understand

  1. Oct 19, 2016 #1
    1. The problem statement, all variables and given/known data
    1) Which solution has the higher pH, a 0.001 M solution of NaOH or a 0.001 M solution of Ba(OH)2?

    2) Would a 1.0 × 10-8M solution of HCl have pH < 7,
    pH = 7, or pH > 7? My professor said she shouldn't have put HCl as the solution, but that it doesn't matter apparently.

    2. Relevant equations

    3. The attempt at a solution
    1) answer is: A 0.001 M solution of Ba(OH)2 has the higher pH

    2) answer is: pH < 7

    My question:

    For 1) How do i determine this? I have no idea how

    For 2) I'm doing pH = -log[1.0 x 10-8] and im getting pH = 8. How is the answer less than 7?
     
    Last edited: Oct 19, 2016
  2. jcsd
  3. Oct 19, 2016 #2

    Bystander

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    Of what?
    Are you conversant with the concepts of stoichiometry?
     
  4. Oct 19, 2016 #3
    It was HCl but she said it doesn't matter.

    Yes i know stoichiometry
     
  5. Oct 19, 2016 #4

    Bystander

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    Please DO NOT edit. It makes it impossible to follow discussions.

    And if the solute were a base? It matters.
    What does stoichiometry tell you?
     
  6. Oct 19, 2016 #5
    I guess I could find the number of moles of OH in each of the molecules using molarity. And the Ba(OH)2 would have 2x the number of moles. If that's right then I could also figure it out if it were two different molarities.
     
  7. Oct 20, 2016 #6

    epenguin

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    Answer to 2 follows directly from definition of pH, and the one you give, I don't know whether it is yours or what you were told, seems wrong to me.

    For 1 you are on the right lines; what do you think are the molarities of everything that is there in that Ba(OH)2 solution?
     
    Last edited: Oct 20, 2016
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