Experimental Buffer Capacity Calculation

[chem.is.try]

I know that buffer capacity is defined as the ability of a buffer to resist pH change. I'm trying to calculate the buffer capacity of my buffer. I added NaOH to it until a significant change in pH, usually about 2 units. So when I calculate, should I do

exp. buffer capacity = (moles NaOH / $$\Delta$$ pH )/ volume of buffer used

i'm basing this formula on this website: http://www.chemicalforums.com/index.php?topic=20361.0

also, if you could give a clearer definition of buffer capacity in terms of experiments and how it should be calculated, that would be great. right now, I'm looking at it as the amount of base needed to change the pH of 1 L of the buffer by 1 unit.

Thanks!

 

[Borek]

There are many possible formulations of buffer capacity definition. As there is no one obligatory definition, recognized by everyone, it is up to you to decide which one you will use.

My favorite is the one explained at ChemBuddy buffer capacity page.

 

[chem.is.try]

Thanks!

what is a normal range for the buffer capacity? like, what kind of values do we normally see?

 

[Borek]

Download Buffer Maker from ChemBuddy page, it has a 30 days free trial, so you don't have to buy it - and play with the program. When you use it to design a buffer it shows a plot of buffer capacity, it should give you some idea about numbers involved.