Titriation Calculation for Weak Acid, Strong Base

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Discussion Overview

The discussion revolves around the titration of a weak acid (acetic acid) with a strong base (sodium hydroxide), specifically focusing on sketching the pH vs. volume of base added curve. Participants explore the calculations and concepts necessary for constructing this titration curve, including the use of dissociation constants and ICE tables.

Discussion Character

  • Homework-related
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant notes that weak acids like acetic acid will dissociate in water, suggesting that the initial concentration of [H+] is not zero and can be calculated using an ICE table.
  • Another participant provides a Ka value for acetic acid (1.75*10^(-5)) and suggests using it along with the expression for Ka to find the concentrations of the species involved in the titration.
  • There is a question about whether the pKa value provided in a previous question can be used in this problem, indicating some uncertainty about the use of previously given information.
  • Links to external resources for titration curve calculations are shared, suggesting that participants are looking for additional tools or references to aid in their understanding.

Areas of Agreement / Disagreement

Participants express differing views on the initial concentration of [H+] and the necessity of the Ka value for acetic acid. There is no consensus on how to proceed with the calculations, and the discussion remains unresolved regarding the best approach to sketch the titration curve.

Contextual Notes

Some participants highlight the lack of a provided Ka value as a limitation, while others suggest looking it up in reference materials. The discussion also reflects uncertainty about the application of previously given values in the current context.

linuxux
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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? I am really stuck here...
 
Last edited:
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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.
 
thanks for help.
 
i got my answer here:
http://www.brynmawr.edu/Acads/Chem/Chem104lc/study/buffer6.html

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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