Appendix H | Ionization Constants of Weak Acids

Ionization Constants of Weak Acids

Acid

Formula

K_a at 25°C

Lewis Structure¹

acetic

CH₃COOH

1.75 × 10^-5

arsenic

H₃AsO₄

5.5 × 10^-3

H₂AsO₄^–

1.7 × 10^-7

HAsO₄^2-

5.1 × 10^-12

arsenous

H₃AsO₃

5.1 × 10^-10

benzoic

C₆H₅COOH

6.25 × 10^-5

boric

H₃BO₃

5.4 × 10^-10

H₂BO₃^–

1 × 10^-14 *

carbonic

H₂CO₃

4.5 × 10^-7

HCO₃^–

4.7 × 10^-11

chlorous

HClO₂

1.1 × 10^-2

cyanic

HOCN

3.5 × 10^-4

formic

HCOOH

1.8 × 10^-4

hydrazoic

HN₃

2 × 10^-5

hydrocyanic

HCN

6.2 × 10^-10

hydrofluoric

HF

6.3 × 10^-4

hydrogen peroxide

H₂O₂

2.4 × 10^-12

hydrogen selenide

H₂Se

1.3 × 10^-4

HSe^–

1.0 × 10^-11

hydrogen sulfide

H₂S

8.9 × 10^-8

HS^–

1 × 10^-19

hydrogen telluride

H₂Te

2 × 10^-3

HTe^–

1 × 10^-11

hypobromous

HOBr

2.8 × 10^-9

hypochlorous

HOCl

4.0 × 10^-8

nitrous

HNO₂

5.6 × 10^-4

oxalic

H₂C₂O₄

5.6 × 10^-2

HC₂O₄^–

1.5 × 10^-4

phenol

C₅H₅OH

1.0 × 10^-10

phosphoric

H₃PO₄

6.9 × 10^-3

H₂PO₄^–

6.2× 10^-8

HPO₄^2-

4.8 × 10^-13

phosphorous

H₃PO₃

5 × 10^-2

H₂PO₃^–

2.0 × 10^-7

sulfuric

H₂SO₄

strong acid

HSO₄^–

1.0 × 10^-2

sulfurous

H₂SO₃

1.4 × 10^-2

HSO₃^–

6 × 10^-8