Ionization Constants of Aqueous Polyprotic Acids

James Richard Fromm


Common Name Formula Constant pKa
Arsenic Acid H3AsO4 K1 = 5.65 x 10-3 2.248
--- H2AsO4- K2 = 1.75 x 10-7 6.757
--- HAsO42- K3 = 2.54 x 10-12 11.596
Boric Acid H3BO3 K1 = 5.78 x 10-10 9.238
Carbonic Acid H2CO3 K1 = 4.35 x 10-7 6.361
--- HCO3- K2 = 4.69 x 10-11 10.329
Chromic Acid H2CrO4 K1 = 3.55 -0.550
--- HCrO4- K2 = 3.36 x 10-7 6.473
Citric Acid HOC(CH2COOH)3 K1 = 7.42 x 10-4 3.130
--- --- K2 = 1.75 x 10-5 4.757
--- --- K3 = 3.99 x 10-6 5.602
EDTA C2H4N2(CH2COOH)4 K1 = 9.81 x 10-3 2.008
--- --- K2 = 2.08 x 10-3 2.683
--- --- K3 = 7.98 x 10-7 6.098
--- --- K4 = 6.60 x 10-11 10.181
Glycinium Ion H3NCH2COOH+ K1 = 4.47 x 10-3 2.350
- (Glycine) H2NCH2COOH K2 = 1.67 x 10-10 9.778
Hydrogen Sulfide H2S K1 = 1.02 x 10-7 6.992
--- HS- K2 = 1.22 x 10-13 12.915
Oxalic Acid HOOCCOOH K1 = 5.40 x 10-2 1.268
--- HOOCCOO- K2 = 5.23 x 10-5 4.282
Phthalic Acid C6H4(COOH)2 K1 = 1.13 x 10-3 2.946
--- --- K2 = 3.90 x 10-6 5.409
Phosphoric Acid H3PO4 K1 = 7.11 x 10-3 2.148
--- H2PO4- K2 = 6.23 x 10-8 7.206
--- HPO4-- K3 = 4.55 x 10-13 12.342
Succinic Acid C(CH2)2COOH K1 = 6.21 x 10-5 4.207
--- HOOC(CH2)2COO- K2 = 2.31 x 10-6 5.636
Sulfuric Acid H2SO4 K1 > 1 Negative
--- HSO4- K2 = 1.01 x 10-2 1.994
Sulfurous Acid H2SO3 K1 = 1.71 x 10-2 1.766
--- HSO3- K2 = 5.98 x 10-8 7.223

Monoprotic Acids Table

Main Tables

Auxiliary Table


Copyright 1997 James R. Fromm