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PH and pOH and [H+] and [OH-] Problems

  1. May 27, 2005 #1
    1. Two HCl(aq) solutions have pH= 2.00 and pH= 3.00, respectively. If equal volumes of these two solutions are combined, the pH of the resulting solution wil be ...

    Now I know the answer is 2.26 but I don't know how to actually solve it..

    2.Aniline(C6H5NH2) is a weak base. At 25C, a 0.100M aqueous solution has a pH of 8.80. The Kb of aniline is..

    Now I know the answer is 4.0x10^-10 but I don't know how to actually solve it..

    3. 60.0ml of .100 M KOH is mixed with 40.0ml of .250M HCl at 25C. Assuming the volumes are additive, what is the pH of the resulting solution?

    1.4 but I don't know how to solve it..

    Please tell me how to do those..I have a chem test tomorrow :bugeye:

  2. jcsd
  3. May 27, 2005 #2
    Calculate the pH of .400M Sr(OH)2

    -log(.800M) = .09691

    pH= 14-pOH= 13.9

    Why is it .800 instead os .400M?

    Is it because there are TWO OH s?
  4. May 27, 2005 #3
    Nevermind this. I figured it out.

    I still need help on the problems in the first thread.
  5. May 27, 2005 #4


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    Staff: Mentor

    1. Assume you are mixing 1L of each solution. Calculate number of moles of HCl in each solution - if you add these numbers you will know how much acid is present. You also know final solution volume. That gives concentration, pH calculation should be easy from this moment on ;)

    2. Aniline reacts with water to produce OH-. Equlibrium of this reaction is described by Kb constant. Check out how you did pH calculation for weak base (or how it is described in your textbook). You must use exactly the same equation and the same simplifying assumptions, just solve for Kb, not H+ (or OH-).

    3. Simple stoichiometry and limiting reagent question - reagent that is left after the neutralization will define pH. If there are exactly the same amounts of reagents autoionization of water will define pH. So check what was left, pH calculation will be just pressing log button on your calculator...

    Chemical calculators at
  6. May 27, 2005 #5

    Thanks for the help! :smile:
  7. May 27, 2005 #6


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    Staff: Mentor

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