Determining Minimum NaOH Amount for 0.4M Acetic Acid Buffer Capacity

In summary, the conversation discusses the smallest amount of solid NaOH that will exceed the buffer capacity of a 500mL buffer containing 0.4M acetic acid and 0.15M NaOAc. The options given are 5.69, 5.16, 4.74, 4.31, and 3.00 grams. One person tries to calculate the answer using the formula 0.4M * 0.5L = 0.2 moles of NaOH, which equates to 8 grams. However, the concept of buffer solutions and their resistance to changes in pH is brought up. The conversation ends with someone asking for the correct answer and discussing the different
  • #1
apchemstudent
220
0
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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  • #2
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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  • #3
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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  • #4
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).
 
  • #6
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.
 
  • #7
First of all - what pH change do you expect?
 

What is buffer capacity?

Buffer capacity refers to the ability of a buffer solution to resist changes in pH when small amounts of acid or base are added. It is a measure of the effectiveness of a buffer in maintaining a stable pH.

How is buffer capacity calculated?

Buffer capacity can be calculated by multiplying the concentration of the buffer by the change in pH divided by the amount of acid or base added. Alternatively, it can be calculated from the Henderson-Hasselbalch equation.

Why is buffer capacity important in biological systems?

In biological systems, maintaining a stable pH is crucial for the proper functioning of enzymes and other biochemical processes. Buffer solutions help to maintain a stable pH, and the buffer capacity determines how well this can be achieved.

What factors affect buffer capacity?

The buffer capacity is affected by the concentrations of the acid and conjugate base in the buffer solution. It also depends on the pH of the solution and the strength of the acid and base used to make the buffer.

How can buffer capacity be increased?

Buffer capacity can be increased by increasing the concentration of the buffer components or by choosing a buffer with a pKa close to the desired pH. Additionally, the addition of a polyprotic acid or base can increase the buffer capacity.

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