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Dissociation Constant of Weak Acids

  1. May 15, 2009 #1
    1. The problem statement, all variables and given/known data
    In my lab, it says that i have to calculate the pH and the Ka of an unknown acid of known concentration (0.20 mol/L)..however, the part that is confusing me is that we first had to obtain 40 mL of that particular unknown acid...

    2. Relevant equations

    3. The attempt at a solution
    I know that [HA]--> <--- [H]+ +[A]- ..i initially thought that it's Ka is simply (0.20)^2/0.20 but i think it's wrong...
  2. jcsd
  3. May 15, 2009 #2


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    You either MEASURE the pH of the unknown acid, or you KNOW THE Ka or identity of the acid. Other than that, you perform a pH titration and make a TITRATION CURVE. Your Ka expression can be coordinated to certain data from your pH titration data (or the curve). Borek has some online guidance that may help with this theory. Another choice is to study the theory of neutralization titrations, especially for weak acids and bases.
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