Buffer solution capacity determination

[Aiva]

I have 3 buffer solutions with 3 components each and 3 buffer solutions with 2 components. I want to compare the capacities.

But first I want to understand what exactlycapacity is and how can I calculate it! I have this page:

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity

1) Consider eq. 9.10. for calculating buffer capacity:

β=2.303(Kw/[H]+[H]+(Cbuf·KaH]

How can one do a sum of Kw/[H] + [H]?
Wouldn't it make you count two variables with different units? Like L/mol plus mol/L?

2) if I calculate buffer capacity β using this formula what would I get? The amont of strong base or acid needed to add to 1L of buffer solution to change pH by 1 unit? Or not?

Some wise words would be appriciated. A lot.

 

[jbsteele]

1) The equation you provided is a simplified version of the Henderson-Hasselbalch equation, which is used to calculate the pH of a buffer solution. Kw/[H] + [H] represents the ratio of the ionic product of water (Kw) and the hydrogen ion concentration ([H]), which is an indication of the buffering capacity of the solution. This ratio of Kw/[H] + [H] helps to determine how much acid or base needs to be added to change the pH of the buffer solution by one unit. 2) The buffer capacity β is the amount of strong base or acid needed to add to 1L of buffer solution to change pH by 1 unit.