A buffer consists of 0.45 M NaH2PO4 and 0.43 M Na2HPO4.?

Question

(Ka1 = 7.2 10-3, Ka2 = 6.3 10-8, and Ka3 = 4.2 10-13).
(a) Which Ka value is most important to this buffer?
b) What is the buffer pH?

Answer 1

(a) Ka2 = 6.3x10^-8(M)
(b) pH = -log(Ka2*[NaH2PO4]/[Na2HPO4]
= -log(6.3x10^-8*0.45/0.43)
= 7.18