# Buffer (buffer capacity)

I know that there already exist multiple questions concerning buffers and buffer capacities, but I would nevertheless like to clarify two things with your help:

1. Adding to a buffer $n$ moles of an acid of negligible volume or a solution of the same acid (also containing $n$ moles of the acid) both produce the same change in $pH$. Correct?

2. However there is a difference between the two, as the latter diminishes the buffer's capacity. How can I observe, from a mathematical standpoint, the decrease in the buffer capacity for the second approach; more precisely: Given,say an acidic buffer solution of volume $V_i$ with $HA$ being the weak acid and $A^-$, its conjugate base (with concentrations $c_a, c_b$ respectively), how does the buffer capacity change upon the addition of a solution of volume $V_s$, containing $n$ moles of a strong base?

Any help would be appreciated.

• Both scenarios decrease buffer capacity if you're consuming the conjugate base. The dilution effect might be important but it depends the concentration of your buffer (if it's dilute, then higher order effects will matter). – Zhe Jun 20 '17 at 17:53