Determining Minimum NaOH Amount for 0.4M Acetic Acid Buffer Capacity

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Discussion Overview

The discussion revolves around determining the minimum amount of solid NaOH required to exceed the buffer capacity of a 500mL buffer solution containing 0.4M acetic acid and 0.15M sodium acetate. The focus includes theoretical understanding of buffer capacity and its implications in practical scenarios.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • One participant calculates that 0.2 moles of NaOH corresponds to 8 grams, questioning their approach to the problem.
  • Another participant suggests that the first contributor should review the concept of buffer solutions, implying a misunderstanding of how buffers function.
  • A later post indicates that there are varying definitions of buffer capacity, noting that it can be defined as the ratio of the amount of strong acid or base added to the resulting change in pH.
  • One participant expresses uncertainty about the expected pH change when adding solid NaOH to the buffer solution.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the definition of buffer capacity and its implications for the problem at hand. There is no consensus on the correct approach or answer to the original question.

Contextual Notes

There are limitations regarding the assumptions made about buffer capacity and the expected pH changes, which remain unresolved in the discussion.

apchemstudent
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What is the smallest amount of solid NaOH that will exceed the buffer capacity 500mL of a buffer that is 0.4M in acetic acid and 0.15M in NaOAc?

a)5.69 b)5.16 c) 4.74 d) 4.31 e)3.00 grams

Since this is a strong base, we only need to deal with the 0.4M of acetic acid.

so 0.4M *.5L = 0.2moles of NaOH

that's 8 grams. What am I doing wrong here?
 
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I think you should read up on what a buffer is.
http://en.wikipedia.org/wiki/Buffer_solution"

Buffer solutions are solutions which resist change in hydronium ion concentration (and consequent pH) upon addition of small amounts of acid or base, or upon dilution

So, can you see why what you did is wrong?
 
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siddharth said:
I think you should read up on what a buffer is.
http://en.wikipedia.org/wiki/Buffer_solution"



So, can you see why what you did is wrong?

oops... i think i got the answer... thanks
 
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Seems there are different definitions of buffer capacity in use. I was taught buffer capacity is defined as the ratio of the amount of strong base or strong acid added to the change in pH - thus you can't say when it will run out - as it is value that you can calculate for a point (as first derivative, dn/dpH, where n - moles).
 
Does anyone know what the answer to that question is? I tried to figure it out but I'm getting enough of a pH change for any of the amount of solid.
 
First of all - what pH change do you expect?
 

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