Effective buffer range?

Question

The Ka for a hypothetical weak acid HX is 3.1 x 10^-5. Buffer solutions containing HX and NaX could be prepared to make a range of pH values. What would be the lower and upper pH values of the effective buffer range?

Answer 1

In general, the effective range for a buffer, assuming appropriate concentry/buffer capacity, is plus or minus 1 pH unit on either side of the pKa. Here, the pKa is 4.5 (-log Ka). So the effective pH range would be from pH 3.5 to pH 5.5.