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Homework Help: Titration question 2 equivalence points. Am i right?

  1. Nov 20, 2009 #1
    Titration question 2!! equivalence points. Am i right?

    1. The problem statement, all variables and given/known data
    this is the originial question.
    A 0.149 g sample of a weak acid (HA) requires 16.80 mL of 0.110 M NaOH to completely reach the equivalence point. What is the Molar Mass of the acid?
    and i got 86.63 g/mol. I have already made sure that it is right.

    the question continues,
    If the pH of the weak acid in question 1 (above) is 4,34 after 8.40 ml of the NaOH was added, what is the Ka of the acid?

    2. Relevant equations

    i think i remember this. At the half equivalence point, PH=PKa

    3. The attempt at a solution

    since PH=Pka at half equivalence point, the PH=10-4.38
    giving me 4.17x10-5

    am i right? :)
  2. jcsd
  3. Nov 20, 2009 #2


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    Gold Member

    Re: Titration question 2!! equivalence points. Am i right?

    Your concept is correct. I did not examine your values, so just trust your concept and you may do your own rechecking of the values.
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