Calculate pH of CH3COOH & NaOH Solution

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Discussion Overview

The discussion revolves around calculating the pH of a solution formed by mixing acetic acid (CH3COOH) and sodium hydroxide (NaOH). The context includes theoretical aspects of acid-base reactions and buffer solutions, with participants exploring different methods to approach the problem.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant expresses uncertainty about how to begin the calculation for the pH of the mixed solution.
  • Another participant suggests that the strong base (NaOH) completely converts acetic acid to acetate and recommends using the expression that defines the acid dissociation constant (Ka).
  • A hint is provided regarding the concept of buffers, implying that the solution may behave as a buffer due to the presence of both the weak acid and its conjugate base.
  • It is proposed that two ICE (Initial, Change, Equilibrium) tables should be set up to outline the concentrations of the weak acid and conjugate base after the reaction with hydroxide ions.
  • One participant argues that a single ICE table may not be necessary and suggests using the Henderson-Hasselbalch equation as a straightforward method for calculating pH.
  • Another participant agrees that the Henderson-Hasselbalch equation is preferred but also emphasizes the importance of understanding concentration ratios for intuition.

Areas of Agreement / Disagreement

Participants present multiple approaches to the problem, with no consensus on a single method. Some advocate for the use of ICE tables, while others prefer the Henderson-Hasselbalch equation, indicating a lack of agreement on the best approach.

Contextual Notes

There are varying assumptions regarding the completeness of the reaction and the necessity of using ICE tables versus the Henderson-Hasselbalch equation. The discussion does not resolve these assumptions.

Rron
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A solution is prepared by mixing 200 mL of 0.2 M CH3COOH with 100 mL of 0.1 M of NaOH solution.Calculate the pH of the solution.(Ka=1.8x10-5)

I really don't know how to start this, so please help me.Its going to be a similar one on my exam tomorrow.

Thanks.
 
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Assume the strong base completely converts the acetic acid to acetate. From there look at the expression which defines Ka for this acid. That's a start.

If you can't see it from that information, try looking over this information.
 
Hint: have you heard about buffers?
 
This is a buffer question. You will need to set up two ICE tables. The first one outlines the remaining concentration of weak acid and conjugate base after the reaction with OH-. The second should use those concentrations to determine the final pH. If you have a book, there should be an example.
 
Actually no need even for a single ICE table, this is almost a simple plug and chug application of the Henderson-Hasselbalch equation. You just need to start calculating concentrations of the reaction products, assuming reaction went to completion.
 
Correct, the Henderson-Hasselbalch equation is the preferred method. If this student does not know where to start, however, I figured writing out the concentration ratios would help in gaining some intuition.
 

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