Determining Minimum NaOH Amount for 0.4M Acetic Acid Buffer Capacity

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The discussion revolves around calculating the minimum amount of solid NaOH required to exceed the buffer capacity of a 0.4M acetic acid and 0.15M sodium acetate solution. Participants initially calculate that 8 grams of NaOH is needed based on the moles of acetic acid, but this is challenged as incorrect. The concept of buffer capacity is clarified, indicating it relates to the ratio of strong acid or base added to the resulting pH change. There is confusion regarding the definition of buffer capacity, with a request for clarification on the expected pH change when adding NaOH. Ultimately, the conversation highlights the complexities of buffer solutions and the importance of understanding their properties.
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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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