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Titriation Calculation for Weak Acid, Strong Base

  • Thread starter linuxux
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  • #1
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Homework Statement



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.

Homework Equations



none, i think.

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...
 
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Answers and Replies

  • #2
symbolipoint
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Linuxux,
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.
 
  • #3
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thanks for help.
 
  • #5
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i got my answer here:
http://www.brynmawr.edu/Acads/Chem/Chem104lc/study/buffer6.html [Broken]

check your answer by comparing you pH/pOH value with the case that applies to you here, http://www.ausetute.com.au/titrcurv.html
 
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