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Titriation Calculation for Weak Acid, Strong Base

  1. Mar 12, 2007 #1
    1. The problem statement, all variables and given/known data

    Sketch curve of pH vs volume of base added for the titration of 50.0ml of 1.00M acetic acid with 1.00M sodium hydroxide.

    2. Relevant equations

    none, i think.

    3. The attempt at a solution

    Okay, first off, this is a weak acid, the first point on the curve would be the initial [H+] in the solution, so pH=-log([H+]). But i thought weak acids have very few H+ ions, almost none, thus the initial [H+]=0, but there is no exponent (other than infinity) that will give you zero, so this must be a situation where you use an ICE table to find [H+], but i was given no Ka value! so how can i solve for "x" in the ICE table? Can someone show me exactly how to find the important points so i can sketch the graph. thanks.

    p.s. the pKa value of acetic acid was given in a previous question, i wonder if i am allowed to use it in this problem? im really stuck here...
    Last edited: Mar 12, 2007
  2. jcsd
  3. Mar 12, 2007 #2


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    Homework Helper
    Education Advisor
    Gold Member

    You need to understand that a weak acid, such as acetic, will dissociate in water, so the dissociation for this acid will be significant. Now about not being given the Ka value for acetic acid, just look in a table of acid dissociation constants. An analytical chemistry textbook here gives a Ka of 1.75*10^(-5). Now, simply make use of the expression and equation for Ka. Keep in mind the amounts of base titrant that you add.

    To start with, having no base yet added, you use something like:

    Ka = (H)*(Ac)/(HAc), in which the items in parentheses are the molar concentrations, using H for hydronium, Ac for acetate anion, HAc for acetic acid.
  4. Mar 13, 2007 #3
    thanks for help.
  5. Mar 13, 2007 #4


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  6. Mar 13, 2007 #5
    Last edited: Mar 13, 2007
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