See below for a table of “Ionization Constants for Select Acids” and a table of “Ionization Constants for Select Bases”.
Note that if the Ka value for an acid is listed, then the corresponding Kb value for its conjugate base will not be listed, and vice versa. So if you cannot find a particular acid, try looking for its conjugate base in the Kb table. Similarly, if you cannot find a particular base, try looking for its conjugate acid in the Ka table.
Ionization Constants for Select Acids
Ka determined at 25 °C.
You can change the number of rows shown per page (navigate using "previous" and "next" at the bottom of the page), or search the table. When searching for multiple Ka's of a polyprotic acid, search for the common part of the molecules (for example, search for PO4 when looking for HxPO4 acids.
| Acid | Formula and Ionization Equation | Ka | pKa |
|---|---|---|---|
|
Acetic
|
CH3COOH + H2O ⇌ H3O+ + CH3COO−
|
1.8 × 10−5
|
4.74 |
|
Arsenic
|
H3AsO4 + H2O ⇌ H3O+ + H2AsO4−
|
K1 = 6.17 × 10−3
|
2.210 |
|
H2AsO4− + H2O ⇌ H3O+ + HAsO42−
|
K2 = 1.17 × 10−7
|
6.932 | |
|
HAsO42− + H2O ⇌ H3O+ + AsO43−
|
K3 = 3.09 × 10−12
|
11.523 | |
|
Benzoic
|
C6H5COOH + H2O ⇌ H3O+ + C6H5COO−
|
1.2 × 10−4
|
3.92 |
|
Boric
|
B(OH)3(H2O) + H2O ⇌ H3O+ + B(OH)4−
|
5.8 × 10−10
|
9.24 |
|
Butyric
|
CH3CH2CH2COOH + H2O ⇌ H3O+ + CH3CH2CH2COO- |
1.5 × 10-5 |
4.82 |
|
Carbonic
|
H2CO3 + H2O ⇌ H3O+ + HCO3−
|
K1 = 4.3 × 10−7
|
6.37 |
|
HCO3− + H2O ⇌ H3O+ + CO32−
|
K2 = 4.7 × 10−11
|
10.33 | |
|
Citric
|
H3C6H5O7 + H2O ⇌ H3O+ + H2C6H5O7−
|
K1 = 1.4 × 10−3
|
2.85 |
|
H2C6H5O7− + H2O ⇌ H3O+ + HC6H5O72−
|
K2 = 4.5 × 10−5
|
4.35 | |
|
HC6H5O72− + H2O ⇌ H3O+ + C6H5O73−
|
K3 = 1.5 × 10−6
|
5.82 | |
|
Chloroacetic
|
CH2ClCOOH + H2O ⇌ H3O+ + CH2ClCOO- |
1.4 × 10-3 |
2.85 |
|
4-chlorobutyric
|
CH2ClCH2CH2COOH + H2O ⇌ H3O+ + CH2ClCH2CH2COO- |
3.0 × 10-5 |
4.53 |
|
3-chlorobutyric acid
|
CH3CHClCH2COOH + H2O ⇌ H3O+ + CH3CHClCH2COO- |
8.9 × 10-5 |
4.05 |
|
2-chlorobutyric acid
|
CH3CH2CHClCOOH + H2O ⇌ H3O+ + CH3CH2CHClCOO- |
1.3 × 10-3 |
2.89 |
|
Chlorous
|
HClO2 + H2O ⇌ H3O+ + ClO2−
|
1.1 × 10−2
|
1.96 |
|
Dichloroacetic
|
CHCl2COOH + H2O ⇌ H3O+ + CHCl2COO- |
4.5 × 10-2 |
1.35 |
|
Formic
|
HCOOH + H2O ⇌ H3O+ + HCOO−
|
1.8 × 10−4
|
3.75 |
|
Hydrazoic
|
HN3 + H2O ⇌ H3O+ + N3−
|
1.0 × 10−5
|
5.00 |
|
Hydrochloric
|
HCl + H2O ⇌ H3O+ + Cl- |
1.2 × 106 |
-6.1 |
|
Hydrocyanic
|
HCN + H2O ⇌ H3O+ + CN−
|
3.3 × 10−10
|
9.48 |
|
Hydrofluoric
|
HF + H2O ⇌ H3O+ + F−
|
6.8 × 10−4
|
3.17 |
|
Hydrogen peroxide
|
H2O2 + H2O ⇌ H3O+ + HO2−
|
2.1 × 10−12
|
11.68 |
|
Hydrosulfuric†
|
H2S + H2O ⇌ H3O+ + HS−
|
K1 = 1 × 10−7
|
7.0 |
|
HS− + H2O ⇌ H3O+ + S2−
|
K2 = 1 × 10−19
|
19.0 | |
|
Hypobromous
|
HOBr + H2O ⇌ H3O+ + OBr- |
3 × 10-9 |
8.5 |
|
Hypochlorous
|
HOCl + H2O ⇌ H3O+ + OCl−
|
6.8 × 10−8
|
7.17 |
|
Hypoiodous
|
HOI + H2O ⇌ H3O+ + OI- |
3 × 10-11 |
10.5 |
|
Nitric
|
HNO3 + H2O ⇌ H3O+ + NO3- |
27 |
-1.43 |
|
Nitrous
|
HNO2 + H2O ⇌ H3O+ + NO2−
|
7.41 × 10−4
|
3.130 |
|
Oxalic
|
H2C2O4 + H2O ⇌ H3O+ + HC2O4−
|
K1 = 5.5 × 10−2
|
1.26 |
|
HC2O4− + H2O ⇌ H3O+ + C2O42−
|
K2 = 1.4 × 10−4
|
3.85 | |
|
Phenol
|
HC6H5O + H2O ⇌ H3O+ + C6H5O−
|
1.7 × 10−10
|
9.77 |
|
Phosphoric
|
H3PO4 + H2O ⇌ H3O+ + H2PO4−
|
K1 = 7.2 × 10−3
|
2.14 |
|
H2PO4− + H2O ⇌ H3O+ + HPO42−
|
K2 = 6.3 × 10−8
|
7.20 | |
|
HPO42− + H2O ⇌ H3O+ + PO43−
|
K3 = 4.6 × 10−13
|
12.34 | |
|
Phosphorous
|
H3PO3 + H2O ⇌ H3O+ + H2PO3−
|
K1 = 2.4 × 10−2
|
1.62 |
|
H2PO3− + H2O ⇌ H3O+ + HPO32−
|
K2 = 2.9 × 10−7
|
6.54 | |
|
Propanoic
|
CH3CH2COOH + H2O ⇌ H3O+ + CH3CH2COO−
|
1.33 × 10−5
|
4.85 |
|
Selenic
|
H2SeO4 + H2O ⇌ H3O+ + HSeO4−
|
K1 = very large
|
--- |
|
HSeO4− + H2O ⇌ H3O+ + SeO42−
|
K2 = 2.2 × 10−2
|
1.66 | |
|
Selenous
|
H2SeO3 + H2O ⇌ H3O+ + HSeO3−
|
K1 = 2.5 × 10−3
|
2.60 |
|
HSeO3− + H2O ⇌ H3O+ + SeO32−
|
K2 = 1.6 × 10−9
|
8.80 | |
|
Sulfuric
|
H2SO4 + H2O ⇌ H3O+ + HSO4−
|
K1 = 4.0 × 103
|
-3.6 |
|
HSO4− + H2O ⇌ H3O+ + SO42−
|
K2 = 1.1 × 10−2
|
1.96 | |
|
Sulfurous
|
H2SO3 + H2O ⇌ H3O+ + HSO3−
|
K1 = 1.7 × 10−2
|
1.77 |
|
HSO3− + H2O ⇌ H3O+ + SO32−
|
K2 = 6.3 × 10−8
|
7.2 | |
|
Tellurous
|
H2TeO3 + H2O ⇌ H3O+ + HTeO3−
|
K1 = 7.1 × 10−7
|
6.15 |
|
HTeO3− + H2O ⇌ H3O+ + TeO32−
|
K2 = 4.0 × 10−9
|
8.40 | |
|
Trichloroacetic
|
CCl3COOH + H2O ⇌ H3O+ + CCl3COO- |
0.17 |
0.77 |
|
Trifluoroacetic
|
CF3COOH + H2O ⇌ H3O+ + CF3COO- |
0.30 |
0.52 |
| Taken from Hogfeldt, E. and Perrin, D. D., Stability Constants of Metal-Ion complexes, 1st ed. Oxford: New York: Pergamon, 1979-1982. International Union of Pure and Applied Chemistry Commission on Equilibrium Data. Also from Serjeant, E. P. and Dempsey, B. (eds.), “Ionization Constants of Organic Acids in Aqueous Solution,” IUPAC Chemical Data Series No. 23, Pergamon Press, Oxford, 1979. †From Myers, R., Journal of Chemical Education, Vol. 63, 1986, pp. 687-690. |
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Ionization Constants for Select Bases
Kb determined at 25 °C.
| Base | Formula and Ionization Equation | Kb | pKb |
|---|---|---|---|
|
Acetylide
|
C2H- + H2O ⇌ OH- + C2H2 |
1 × 1011 |
-11 |
|
Amide
|
NH2- + H2O ⇌ OH- + NH3 |
1 × 1020 |
-20 |
|
Ammonia‡
|
NH3 + H2O ⇌ NH4+ + OH−
|
1.77 × 10−5
|
4.752 |
|
Aniline§
|
C6H5NH2 + H2O ⇌ C6H5NH3+ + OH−
|
3.9 × 10−10
|
9.41 |
|
Dimethylamine§
|
(CH3)2NH + H2O ⇌ (CH3)2NH2+ + OH−
|
5.8 × 10−4
|
3.24 |
|
Ethoxide
|
CH3CH2O- + H2O ⇌ OH- + CH3CH2OH |
1 × 102 |
-2 |
|
Ethylenediamine
|
(CH2)2(NH2)2 + H2O ⇌ (CH2)2(NH2)2H+ + OH−
|
K1 = 7.8 × 10−5
|
4.11 |
|
(CH2)2(NH2)2H+ + H2O ⇌ (CH2)2(NH2)2H22+ + OH−
|
K2 = 2.1 × 10−8
|
7.68 | |
|
Hydrazine
|
N2H4 + H2O ⇌ N2H5+ + OH−
|
K1 = 1.2 × 10−6
|
5.92 |
|
N2H5+ + H2O ⇌ N2H62+ + OH−
|
K2 = 1.3 × 10−15
|
14.89 | |
|
Hydride
|
H- + H2O ⇌ OH- + H2 |
1 × 1021 |
-21 |
|
Hydroxylamine
|
NH2OH + H2O ⇌ NH3OH+ + OH−
|
9.3 × 10−9
|
8.03 |
|
Methylamine
|
CH3NH2 + H2O ⇌ CH3NH3+ + OH−
|
5.0 × 10−4
|
3.30 |
|
Pyridine
|
C5H5N + H2O ⇌ C5H5NH+ + OH−
|
1.6 × 10−9
|
8.80 |
|
Trimethylamine§
|
(CH3)3N + H2O ⇌ (CH3)3NH+ + OH−
|
6.2 × 10−5
|
4.21 |
| Taken from Hogfeldt, E. and Perrin, D. D., Stability Constants of Metal-Ion complexes, 1st ed. Oxford: New York: Pergamon, 1979-1982. International Union of Pure and Applied Chemistry Commission on Equilibrium Data. Also from Serjeant, E. P. and Dempsey, B. (eds.), “Ionization Constants of Organic Acids in Aqueous Solution,” IUPAC Chemical Data Series No. 23, Pergamon Press, Oxford, 1979. ‡From Read, A. J., Journal of Solution Chemistry, Vol. 11, No. 9, 1982, pp. 649-664. §From Meites, L., Ed. Handbook of Analytical Chemistry, 1st ed. New York: McGraw-Hill, 1963. |
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