(1)H2PO4- HPO42- + H+
(2) Ka2== [H+][HPO42-]/[H2PO4-]
(3)[HPO42-]/[H2PO4-] ==0.04 == 1/25
(4)磷酸氢二钠与磷酸氢钠按1：25 比例混和溶于水!
(5)使二者总浓度达到0.1mol/L!