Acid-Base Ionization Constant

Ionization Constants for Select Acids (a table for bases is below)

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 × 105

4.74

Arsenic

H3AsO4 + H2O ⇌ H3O+ + H2AsO4

K1 = 6.17 × 103

2.210

H2AsO4 + H2O ⇌ H3O+ + HAsO42

K2 = 1.17 × 107

6.932

HAsO42 + H2O ⇌ H3O+ + AsO43

K3 = 3.09 × 1012

11.523

Benzoic

C6H5COOH + H2O ⇌ H3O+ + C6H5COO

1.2 × 104

3.92

Boric

B(OH)3(H2O) + H2O ⇌ H3O+ + B(OH)4

5.8 × 1010

9.24

Butyric

CH3CH2CH2COOH + H2O ⇌ H3O+ + CH3CH2CH2COO-

1.5 × 10-5

4.82

Carbonic

H2CO3 + H2O ⇌ H3O+ + HCO3

K1 = 4.3 × 107

6.37

HCO3+ H2O ⇌ H3O+ + CO32

K2 = 4.7 × 1011

10.33

Citric

H3C6H5O7 + H2O ⇌ H3O+ + H2C6H5O7

K1 = 1.4 × 103

2.85

H2C6H5O7 + H2O ⇌ H3O+ + HC6H5O72

K2 = 4.5 × 105

4.35

HC6H5O72 + H2O ⇌ H3O+ + C6H5O73

K3 = 1.5 × 106

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 × 102

1.96

Dichloroacetic

CHCl2COOH + H2O ⇌ H3O+ + CHCl2COO-

4.5 × 10-2

1.35

Formic

HCOOH + H2O ⇌ H3O+ + HCOO

1.8 × 104

3.75

Hydrazoic

HN3 + H2O ⇌ H3O+ + N3

1.0 × 105

5.00

Hydrochloric

HCl + H2O ⇌ H3O+ + Cl-

1.2 × 106

-6.1

Hydrocyanic

HCN + H2O ⇌ H3O+ + CN

3.3 × 1010

9.48

Hydrofluoric

HF + H2O ⇌ H3O+ + F

6.8 × 104

3.17

Hydrogen peroxide

H2O2 + H2O ⇌ H3O+ + HO2

2.1 × 1012

11.68

Hydrosulfuric

H2S + H2O ⇌ H3O+ + HS

K1 = 1 × 107

7.0

HS + H2O ⇌ H3O+ + S2

K2 = 1 × 1019

19.0

Hypobromous

HOBr + H2O ⇌ H3O+ + OBr-

3 × 10-9

8.5

Hypochlorous

HOCl + H2O ⇌ H3O+ + OCl

6.8 × 108

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 × 104

3.130

Oxalic

H2C2O4 + H2O ⇌ H3O+ + HC2O4

K1 = 5.5 × 102

1.26

HC2O4 + H2O ⇌ H3O+ + C2O42

K2 = 1.4 × 104

3.85

Phenol

HC6H5O + H2O ⇌ H3O+ + C6H5O

1.7 × 1010

9.77

Phosphoric

H3PO4 + H2O ⇌ H3O+ + H2PO4

K1 = 7.2 × 103

2.14

H2PO4 + H2O ⇌ H3O+ + HPO42

K2 = 6.3 × 108

7.20

HPO42 + H2O ⇌ H3O+ + PO43

K3 = 4.6 × 1013

12.34

Phosphorous

H3PO3 + H2O ⇌ H3O+ + H2PO3

K1 = 2.4 × 102

1.62

H2PO3 + H2O ⇌ H3O+ + HPO32

K2 = 2.9 × 107

6.54

Propanoic

CH3CH2COOH + H2O ⇌ H3O+ + CH3CH2COO

1.33 × 105

4.85

Selenic

H2SeO4 + H2O ⇌ H3O+ + HSeO4

K1 = very large

---

HSeO4 + H2O ⇌ H3O+ + SeO42

K2 = 2.2 × 102

1.66

Selenous

H2SeO3 + H2O ⇌ H3O+ + HSeO3

K1 = 2.5 × 103

2.60

HSeO3 + H2O ⇌ H3O+ + SeO32

K2 = 1.6 × 109

8.80

Sulfuric

H2SO4 + H2O ⇌ H3O+ + HSO4

K1 = 4.0 × 103

-3.6

HSO4 + H2O ⇌ H3O+ + SO42

K2 = 1.1 × 102

1.96

Sulfurous

H2SO3 + H2O ⇌ H3O+ + HSO3

K1 = 1.7 × 102

1.77

HSO3 + H2O ⇌ H3O+ + SO32

K2 = 6.3 × 108

7.2

Tellurous

H2TeO3 + H2O ⇌ H3O+ + HTeO3

K1 = 7.1 × 107

6.15

HTeO3 + H2O ⇌ H3O+ + TeO32

K2 = 4.0 × 109

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.

 

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 × 105

4.752

Aniline§

C6H5NH2 + H2O ⇌ C6H5NH3+ + OH

3.9 × 1010

9.41

Dimethylamine§

(CH3)2NH + H2O ⇌ (CH3)2NH2+ + OH

5.8 × 104

3.24

Ethoxide

CH3CH2O- + H2O ⇌ OH- + CH3CH2OH

1 × 102

-2

Ethylenediamine

(CH2)2(NH2)2 + H2O ⇌ (CH2)2(NH2)2H+ + OH

K1 = 7.8 × 105

4.11

(CH2)2(NH2)2H+ + H2O ⇌ (CH2)2(NH2)2H22+ + OH

K2 = 2.1 × 108

7.68

Hydrazine

N2H4 + H2O ⇌ N2H5+ + OH

K1 = 1.2 × 106

5.92

N2H5+ + H2O ⇌ N2H62+ + OH

K2 = 1.3 × 1015

14.89

Hydride

H- + H2O ⇌ OH- + H2

1 × 1021

-21

Hydroxylamine

NH2OH + H2O ⇌ NH3OH+ + OH

9.3 × 109

8.03

Methylamine

CH3NH2 + H2O ⇌ CH3NH3+ + OH

5.0 × 104

3.30

Pyridine

C5H5N + H2O ⇌ C5H5NH+ + OH

1.6 × 109

8.80

Trimethylamine§

(CH3)3N + H2O ⇌ (CH3)3NH+ + OH

6.2 × 105

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.

License

Icon for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

Chemistry 109 Fall 2021 by John Moore, Jia Zhou, and Etienne Garand is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.