This page has acidity tables for monoprotic acids and polyprotic acids.

Ionization Constants of Inorganic Monoprotic Acids

Common Name

Formula

Acidity Constant

pKa

perchloric acid

HClO4

ca. 1010

ca. -10

hydrogen iodide

HI

ca. 109

ca. -9

hydrogen bromide

HBr

ca. 109

ca. -9

hydrogen chloride

HCl

ca. 107

ca. -7

nitric acid

HNO3

ca. 200

ca. -2

thiocyanic acid

HSCN

70

-1.85

hydronium ion

H3O+

55

-1.74

chloric acid

HClO3

10

-1.0

iodic acid

HIO3

0.18

0.75

hypophosphorous acid

H2P(O)OH

10-2

2.0

hydrogen fluoride

HF

6.6 * 10-4

3.2

nitrous acid

HNO2

5.0 * 10-4

3.3

cyanic acid

HOCN

3.54 * 10-4

3.45

hydrazoic acid

HN3

2.37 * 10-5

4.63

hypochlorous acid

HOCl

2.95 * 10-8

7.53

hypobromous acid

HOBr

2.3 * 10-9

8.65

hydrocyanic acid

HCN

5.8 * 10-10

9.25

ammonium

NH4+

5.8 * 10-10

9.25

hypoiodous acid

HOI

10-10

10

hydrogen peroxide

H2O2

2.5 * 10-12

11.6

water

H2O

1.82 * 10-16

15.74

heavy water

D2O

3.5 * 10-17

16.55

ammonia

NH3

ca. 10-34

ca. 34

   

Organic Chemistry
Michigan State University



Ionization Constants of Inorganic Polyprotic Acids

Common Name

Formula

Acidity Constant

pKa

sulfuric acid

H2SO4
HSO4-1

K1 = 2.4 * 106
K2 = 1.0 * 10-2

-6.62   
1.99  

chromic acid

H2CrO4
HCrO4-1

K1 = 3.55
K2 = 3.36 * 10-7

-0.55  
6.47  

sulfurous acid

H2SO3
HSO3-1

K1 = 1.71 * 10-2
K2 = 5.98 * 10-8

1.77  
7.22  

phosphoric acid

H3PO4
H2PO4-1
HPO4-2

K1 = 7.1 * 10-3
K2 = 6.2 * 10-8
K3 = 4.6 * 10-13

2.15  
7.21  
12.34  

phosphorous acid

H3PO3
H2PO3-1

K1 = 1.6 * 10-2
K2 = 6.3 * 10-7

1.8  
6.2  

pyrophosphoric acid

H4P2O7
H3P2O7-1
H2P2O7-2
HP2O7-3

K1 = 3 * 10-2
K2 = 4.4 * 10-3
K3 = 2.5 * 10-7
K4 = 5.6 * 10-10

1.52  
2.36  
6.60  
9.25  

carbonic acid

H2CO3
HCO3-1

K1 = 4.35 * 10-7
K2 = 4.69 * 10-11

6.36  
10.33  

hydrogen sulfide

H2S
HS-1

K1 = 9 * 10-8
K2 = ca.10-15

6.97  
ca.15  

boric acid

H3BO3
H2BO3-1
HBO3-2

K1 = 7.2 * 10-10
K2 = 1.8 * 10-13
K3 = 1.6 * 10-14

9.14  
12.7  
13.8  

   

Organic Chemistry
Michigan State University