配制pH=7的缓冲溶液,选择最合适的缓冲对是[Ka(HAc)=1.8x10^-5;Kb(NH3)=1.8x10^-5;H2CO3:Ka1=4.2x10^-7,Ka2=5.6x10^-11;H3PO4:Ka1=7.6x10^-3,Ka2=6.3x10^-8,Ka3=4.4x10^-13]()A.HAc-NaAcB.NH3-NH4ClC.NaH2PO4-Na2HPO4D.NaHCO3-Na2CO3应该怎么

Question

配制pH=7的缓冲溶液,选择最合适的缓冲对是[Ka(HAc)=1.8x10^-5;Kb(NH3)=1.8x10^-5;H2CO3:Ka1=4.2x10^-7,Ka2=5.6x10^-11;H3PO4:Ka1=7.6x10^-3,Ka2=6.3x10^-8,Ka3=4.4x10^-13] ( )
A.HAc-NaAc B.NH3-NH4Cl
C.NaH2PO4-Na2HPO4
D.NaHCO3-Na2CO3
应该怎么作?

Answer 1

应选用NaH2PO4 —— Na2HPO4缓冲对
H2PO4^1- —— H+ + HPO4^2-
[H+]=Ka*[H2PO4^-]/[HPO4^2-]
H2PO4^-的Ka=6.3*10^-8 PKa=7.2
缓冲范围在PKa加减1范围内,即：PH=6.2—8.2