Buffer solution

Question

Calculate the buffer range of these buffer solutions: (a) NH4Cl-NH3; pK (NH)=4.75

(b) KH2PO-Na₂HPO4; pKa1(H3PO4)=2.16, pK 2(H3PO4)=7.21, PK (H3PO4)=12.32

(c) Na₂HPO-Na3PO4

Answer 1

In general, the "useful" buffer range is the pKa ± 1 pH unit.

(a) 4.75 ± 1 pH unit = pH 3.75 - pH 5.75

(b) 7.21 ± 1 pH unit = pH 6.21 - pH 8.21

(c) 12.32 ± 1 pH unit = pH 11.32 - pH 13.32