Ionization Constants of Weak Acids

Acid Formula <emKa at 25 °C Lewis Structure
acetic CH3CO2H 1.8×10−51.8×10−5
arsenic H3AsO4 5.5×10−35.5×10−3
H2AsO4− 1.7×10−71.7×10−7
HAsO42− 5.1×10−125.1×10−12
arsenous H3AsO3 5.1×10−105.1×10−10
boric H3BO3 5.4×10−105.4×10−10
carbonic H2CO3 4.3×10−74.3×10−7
HCO3− 5.6×10−115.6×10−11
cyanic HCNO 2×10−42×10−4
formic HCO2H 1.8×10−41.8×10−4
hydrazoic HN3 2.5×10−52.5×10−5
hydrocyanic HCN 4.9×10−104.9×10−10
hydrofluoric HF 3.5×10−43.5×10−4
hydrogen peroxide H2O2 2.4×10−122.4×10−12
hydrogen selenide H2Se 1.29×10−41.29×10−4
HSe– 1×10−121×10−12
hydrogen sulfate ion HSO4− 1.2×10−21.2×10−2
hydrogen sulfide H2S 8.9×10−88.9×10−8
HS– 1.0×10−191.0×10−19
hydrogen telluride H2Te 2.3×10−32.3×10−3
HTe– 1.6×10−111.6×10−11
hypobromous HBrO 2.8×10−92.8×10−9
hypochlorous HClO 2.9×10−82.9×10−8
nitrous HNO2 4.6×10−44.6×10−4
oxyalic H2C2O4 6.0×10−26.0×10−2
HC2O4− 6.1×10−56.1×10−5
phosphoric H3PO4 7.5×10−37.5×10−3
H2PO4− 6.2×10−86.2×10−8
HPO42− 4.2×10−134.2×10−13
phosphorous H3PO3 5×10−25×10−2
H2PO3− 2.0×10−72.0×10−7
sulfurous H2SO3 1.6×10−21.6×10−2
HSO3− 6.4×10−86.4×10−8