posted by Tom .
what is the pH range of the buffering region?
is that when ph=pKa?
The best buffering is when pH = pKa. The RANGE, however, generally is considered to be +/- 1 from pKa. That's the definition of buffering capacity.
so if the pka is 4.5 the range will be from 3.5 to 5.5?
You can read more about it here.
I think the buffer capacity is associated with the buffer range. The buffer capacity is defined as the amount of acid or base that can be added without exceeding +/- 1 in pH. The buffer range is the pH range that can be experience by the solution and still act as a buffer. And that is generally +/- 1 pH unit. Yes, in your case, that would be 3.5 to 5.5. A buffer with pKa 4.5 would be expected to work very well withing that range and would not be expected to work well outside that range.