Acid/Base Ionization Constants

Please note: Although these values are common (and published) values associated with the substances given, there are many possible sources for these values. Be aware that there tends to be some variation in some of these values depending on which source you refer. One should always know which source to use. These are established reference values in many books - but be aware of slight differences when working problems.

Having said all that, we (UT Chemistry) will give you the values that we use for exams. The student should know that these values will be given on an exam.

Ka values for some common acids

Name Formula Ka pKa
acetic acid CH3COOH 1.8 × 10-5 4.74
acrylic acid CH2CHCOOH 5.6 × 10-5 4.25
benzoic acid C6H5COOH 6.4 × 10-5 4.19
boric acid H3BO3 5.8 × 10-10 9.24
butanoic acid CH3CH2CH2COOH 1.5 × 10-5 4.82
chloroacetic acid CH2ClCOOH 1.4 × 10-3 2.85
chlorous acid HClO2 1.2 × 10-2 1.92
formic acid HCOOH 1.8 × 10-4 3.74
hydrocyanic acid HCN 6.2 × 10-10 9.21
hydrofluoric acid HF 6.3 × 10-4 3.20
hydrogen peroxide H2O2 2.4 × 10-12 11.62
hypobromous acid HBrO 2.0 × 10-9 8.70
hypochlorous acid HClO 3.5 × 10-8 7.46
hypoiodous acid HIO 2.0 × 10-11 10.70
lactic acid CH3CH(OH)COOH 1.38 × 10-4 3.86
nitrous acid HNO2 4.0 × 10-4 3.40
phenol C6H5OH 1.6 × 10-10 9.80
propanoic acid CH3CH2COOH 1.3 × 10-5 4.89
trichloroacetic acid CCl3COOH 2.2 × 10-1 0.66

Kb values for some common bases

Name Formula Kb pKb
ammonia NH3 1.8 × 10-5 4.74
aniline C6H5NH2 4.3 × 10-10 9.37
dimethylamine (CH3)2NH 5.4 × 10-4 3.27
ethylamine C2H5NH2 5.6 × 10-4 3.25
hydrazine NH2NH2 1.7 × 10-6 5.77
hydroxylamine NH2OH 1.1 × 10-8 7.96
methylamine CH3NH2 4.38 × 10-4 3.36
nicotine C10H14N2 1.0 × 10-6 6.00
piperidine C5H10NH 1.3 × 10-3 2.89
propylamine C3H7NH2 3.7 × 10-4 3.43
pyridine C5H5N 1.8 × 10-9 8.74
triethylamine (C2H5)3N 1.0 × 10-3 3.00
trimethylamine (CH3)3N 6.5 × 10-5 4.19

Ka values for some polyprotic acids

Name Formula Ka pKa
arsenic acid H2AsO4 1) 5.0 × 10-3
2) 9.3 × 10-8
3) 3.0 × 10-12 		1) 2.30
2) 7.03
3) 11.52
carbonic acid H2CO3 1) 4.3 × 10-7
2) 5.6 × 10-11 		1) 6.37
2) 10.25
citric acid H3C6H5O6 1) 8.4 × 10-4
2) 1.8 × 10-5
3) 4.0 × 10-6 		1) 3.08
2) 4.74
3) 5.40
oxalic acid H2C2O4 1) 6.5 × 10-2
2) 6.1 × 10-5 		1) 1.19
2) 4.21
phosphoric acid H3PO4 1) 7.5 × 10-3
2) 6.2 × 10-8
3) 4.8 × 10-13 		1) 2.12
2) 7.21
3) 12.32
sulfuric acid H2SO4 1) ~100
2) 1.2 × 10-2 		1) -2
2) 1.92
sulfurous acid H2SO3 1) 1.5 × 10-2
2) 1.0 × 10-7 		1) 1.82
2) 7.00