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.
http://www.cartage.org.lb/en/themes/Sciences/Chemistry/Inorganicchemistry/AcidsBases/Acidsbasesindex/Bufferrange/Bufferrange.htm
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.
The buffering region is a range of pH values where a buffer solution can effectively resist changes in pH upon addition of small amounts of acid or base. The pH range of the buffering region is generally considered to be within 1 unit above or below the pKa value of the buffer.
The pKa is the negative logarithm (base 10) of the acid dissociation constant (Ka) of the weak acid in the buffer solution. In this context, the pKa represents the pH at which the weak acid is 50% dissociated. When the pH equals the pKa, the concentrations of the weak acid and its conjugate base are equal.
In the buffering region, if an acid or base is added to the buffer solution, the buffer components can either accept or donate protons (H+) to maintain the pH within the desired range. This ability to resist changes in pH is due to the presence of both the weak acid and its conjugate base.
Therefore, while the pH range of the buffering region is generally within 1 unit above or below the pKa value, it is not limited to just when pH equals pKa. The buffer solution can still effectively resist changes in pH even if the pH is slightly different from the pKa value.