# Buffer Capacity

1. Apr 4, 2006

### apchemstudent

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?

2. Apr 4, 2006

### siddharth

I think you should read up on what a buffer is.
http://en.wikipedia.org/wiki/Buffer_solution" [Broken]

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

Last edited by a moderator: May 2, 2017
3. Apr 4, 2006

### apchemstudent

oops... i think i got the answer... thanks

Last edited by a moderator: May 2, 2017
4. Apr 5, 2006

### Staff: Mentor

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).

5. Apr 8, 2006

6. Apr 5, 2007

### Geir

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. Apr 8, 2007

### Staff: Mentor

First of all - what pH change do you expect?