Analytical Chemistry

Table 3.3 pKa values for some Lowry–Brønsted acids

Acid pK 1 pK 2 pK 3 pK 4

acetic

CH 3 COOH

4.76

ammonium

9.25

chloracetic

CH 2 ClCOOH

2.86

diethanolammonium

9.00

ethanolammonium

NH 3 (CH 2 CH 2 OH)+

9.49

ethylenediaminetetraacetic (EDTA) (HOOCCH 2 )

2 N–CH 2 – CH 2 – N(CH 2 COOH) 2

2.0 2.67 6.16 10.27

formic

HCOOH

3.75

hydrocyanic

HCN

9.22

nitric

HNO 3

– 1.4

nitrilotriacetic

(NTA) N(CH 2 COOH) 3

1.66 2.95 10.28

nitrous

HNO 2

3.29

phenol

C 6 H 5 OH

9.98

phosphoric

H 3 PO 4

2.17 7.21 12.36

sulphuric

H 2 SO 4

– 1.96

sulphurous

H 2 SO 3

1.76 7.21

alone, the pH axis is graduated in units of pH relative to PKa and the horizontal axis in the fractional

concentrations of the two species αAH, and αA–, which are given by