CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 380
and
A−+ H 2 O = HA + OH−. (11.68)
The equilibrium constant of the reaction (11.68) is called thehydrolytic constant. We write
Kh=aHAaOH−
aA−aH 2 O. (11.69)
In dilute solutions the equation simplifies to
Kh=cHAcOH−
cA−1
cst. (11.70)
The following relation applies between the hydrolytic constant Kh, the ionic product of
waterKwand the dissociation constantKof a weak acid HA
Kh=Kw
K. (11.71)
11.5.9 Hydrolysis of the salt of a weak base and a strong acid
The following reactions proceed in the solutions of the salts of a weak base and a strong acid
BCl
BCl −→B++ Cl− (11.72)
and
B++ H 2 O = BOH + H+. (11.73)
The equilibrium constant of reaction (11.73) is also called thehydrolytic constant. We write
Kh=aBOHaH+
aB+aH 2 O. (11.74)
In dilute solutions the equation simplifies to
Kh=cBOHcH+
cB+1
cst. (11.75)
Relation (11.71) also applies for the hydrolytic constant of reaction (11.72), withKstanding
for the dissociation constant of a weak base this time.