Page 1
Salt Hydrolysis
Acid + Base ? ? ? Salt + H
2
O neutralization
Salt + H
2
O ? ? ? Acid + Base ? ? ? reverse of neutralization ? Salt hydrolysis
since salt hydrolysis is an endothermic reaction hence on increasing the temperature, the extent
of hydrolysis increases.
? Types of salt
Case I Case II Case III Case IV
Page 2
Salt Hydrolysis
Acid + Base ? ? ? Salt + H
2
O neutralization
Salt + H
2
O ? ? ? Acid + Base ? ? ? reverse of neutralization ? Salt hydrolysis
since salt hydrolysis is an endothermic reaction hence on increasing the temperature, the extent
of hydrolysis increases.
? Types of salt
Case I Case II Case III Case IV
W. A + S. B S. A. + W. B. W. A + W. B. S. A. + S. B.
e.g. CH
3
COONa e.g. NH
4
Cl e.g. CH
3
COONH
4
e.g. NaCl
?Case : (I) Hydrolysis of WA + SB :
CH
3
COONa
? ? ?
CH
3
COO
–
+ Na
+
? spectator ion
?
?
Very strong Very weak
Conjugate base Conjugate acid
H – OH
CH
3
COOH NaOH
CH
3
COO
–
+ H
+
Na
+
+ OH
–
CH
3
COONa CH
3
COO
–
+ Na
+
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
__________________________________________
CH
3
COONa + H
2
O CH
3
COOH + Na
+
+ OH
–
__________________________________________________________________________
Note : (1) Only weaker part of salt undergoes hydrolysis. (2) This solution becomes basic.
?Case : (II) S.A. + W.B. (NH
4
Cl) :
NH
4
+
+ H
2
O NH
4
OH + H
+
, This solution becomes acidic
?Case : (III) W.A. + W.B. (CH
3
COONH
4
)
:
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
a x
a – x
NH
4
+
+ H
2
O NH
4
OH + H
+
a y
a – y
Can be acidic, basic or neutral
? acidic K K
b a
? ? neutral K K
b a
? ? basic K K
b a
? ?
?Case : (IV) S. A + S. B (NaCl) :
? No hydrolysis ? Solution will be neutral
? Relationship between K
a
, K
b
, and K
h
?Case (I) : W. A. + S.B. (CH
3
COONa)
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
] [OH COOH] [CH
K
–
–
–
3
?
?
? ?
K
K ?
Page 3
Salt Hydrolysis
Acid + Base ? ? ? Salt + H
2
O neutralization
Salt + H
2
O ? ? ? Acid + Base ? ? ? reverse of neutralization ? Salt hydrolysis
since salt hydrolysis is an endothermic reaction hence on increasing the temperature, the extent
of hydrolysis increases.
? Types of salt
Case I Case II Case III Case IV
W. A + S. B S. A. + W. B. W. A + W. B. S. A. + S. B.
e.g. CH
3
COONa e.g. NH
4
Cl e.g. CH
3
COONH
4
e.g. NaCl
?Case : (I) Hydrolysis of WA + SB :
CH
3
COONa
? ? ?
CH
3
COO
–
+ Na
+
? spectator ion
?
?
Very strong Very weak
Conjugate base Conjugate acid
H – OH
CH
3
COOH NaOH
CH
3
COO
–
+ H
+
Na
+
+ OH
–
CH
3
COONa CH
3
COO
–
+ Na
+
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
__________________________________________
CH
3
COONa + H
2
O CH
3
COOH + Na
+
+ OH
–
__________________________________________________________________________
Note : (1) Only weaker part of salt undergoes hydrolysis. (2) This solution becomes basic.
?Case : (II) S.A. + W.B. (NH
4
Cl) :
NH
4
+
+ H
2
O NH
4
OH + H
+
, This solution becomes acidic
?Case : (III) W.A. + W.B. (CH
3
COONH
4
)
:
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
a x
a – x
NH
4
+
+ H
2
O NH
4
OH + H
+
a y
a – y
Can be acidic, basic or neutral
? acidic K K
b a
? ? neutral K K
b a
? ? basic K K
b a
? ?
?Case : (IV) S. A + S. B (NaCl) :
? No hydrolysis ? Solution will be neutral
? Relationship between K
a
, K
b
, and K
h
?Case (I) : W. A. + S.B. (CH
3
COONa)
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
] [OH COOH] [CH
K
–
–
–
3
?
?
? ?
K
K ?
?Case (II) : S. A. + W. B. (NH
4
OH)
NH
4
+
+ H
2
O NH
4
OH + H
+
?
] [NH
] [H OH] [NH
K
4
4
h
?
?
?
?
] [OH ] [NH
] [OH ] [H OH] [NH
K
–
4
–
4
h
?
?
?
?
?
?
b
w
h
K
K
K ?
?Case (III) W. A. + W. B. (CH
3
COO NH
4
)
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
NH
4
+
+ H
2
O NH
4
OH + H
+
_______________________________________________________
CH
3
COO
–
+ NH
4
+
+ 2 H
2
O NH
4
OH + CH
3
COOH + H
+
+ OH
–
_______________________________________________________
?
] [NH ] COO [CH
COOH] [CH OH] [NH
K
4
–
3
3 4
h
?
?
?
] [H ] COO [CH
] [H ] [OH COOH] [CH
] [OH ] [NH
OH] [NH
K
–
3
–
3
–
4
4
h
?
?
?
?
?
b a
w
h
K . K
K
K ?
? pH calculation
?Case (I) : W. A. + S. B. (CH
3
COONa ? c, K
a
) , h ? degree of hydrolysis.
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
c 0 0
c (1 – h) ch ch
?
h – 1
ch
h) – (1 c
(ch)
K
2 2
h
? ?
h < < 1 ? K
h
= ch
2
?
c
K
h
h
?
?
a
w
h
–
K
K
c. K c. h c ] [OH ? ? ? ? ?
c] log – pK – [pK
2
1
pOH
a w
?
?
c] log pK [pK
2
1
pH
a w
? ? ?
?Case (II) :S. A. + W. B. (NH
4
Cl ? c, K
b
)
NH
4
+
+ H
2
O NH
4
OH + H
+
c 0 0
c (1 – h) ch ch
?
h – 1
ch
K
2
h
? h < < 1 ? K
h
= ch
2
?
c
K
h
h
?
?
K
K
c K c c.h ] [H
b
w
h
? ? ? ? ?
?
?
c] log – pK – [pK
2
1
pH
b w
?
? p
OH
=
? ? c log p p
2
1
b w
k k
? ?
?Case (III) W. A. + W. B. (CH
3
COONH
4
? K
a
, K
b
, c)
CH
3
COO
–
+ NH
4
+
+ H
2
O NH
4
OH + CH
3
COOH
c c
c (1 – h) c (1 – h) ch ch
Page 4
Salt Hydrolysis
Acid + Base ? ? ? Salt + H
2
O neutralization
Salt + H
2
O ? ? ? Acid + Base ? ? ? reverse of neutralization ? Salt hydrolysis
since salt hydrolysis is an endothermic reaction hence on increasing the temperature, the extent
of hydrolysis increases.
? Types of salt
Case I Case II Case III Case IV
W. A + S. B S. A. + W. B. W. A + W. B. S. A. + S. B.
e.g. CH
3
COONa e.g. NH
4
Cl e.g. CH
3
COONH
4
e.g. NaCl
?Case : (I) Hydrolysis of WA + SB :
CH
3
COONa
? ? ?
CH
3
COO
–
+ Na
+
? spectator ion
?
?
Very strong Very weak
Conjugate base Conjugate acid
H – OH
CH
3
COOH NaOH
CH
3
COO
–
+ H
+
Na
+
+ OH
–
CH
3
COONa CH
3
COO
–
+ Na
+
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
__________________________________________
CH
3
COONa + H
2
O CH
3
COOH + Na
+
+ OH
–
__________________________________________________________________________
Note : (1) Only weaker part of salt undergoes hydrolysis. (2) This solution becomes basic.
?Case : (II) S.A. + W.B. (NH
4
Cl) :
NH
4
+
+ H
2
O NH
4
OH + H
+
, This solution becomes acidic
?Case : (III) W.A. + W.B. (CH
3
COONH
4
)
:
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
a x
a – x
NH
4
+
+ H
2
O NH
4
OH + H
+
a y
a – y
Can be acidic, basic or neutral
? acidic K K
b a
? ? neutral K K
b a
? ? basic K K
b a
? ?
?Case : (IV) S. A + S. B (NaCl) :
? No hydrolysis ? Solution will be neutral
? Relationship between K
a
, K
b
, and K
h
?Case (I) : W. A. + S.B. (CH
3
COONa)
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
] [OH COOH] [CH
K
–
–
–
3
?
?
? ?
K
K ?
?Case (II) : S. A. + W. B. (NH
4
OH)
NH
4
+
+ H
2
O NH
4
OH + H
+
?
] [NH
] [H OH] [NH
K
4
4
h
?
?
?
?
] [OH ] [NH
] [OH ] [H OH] [NH
K
–
4
–
4
h
?
?
?
?
?
?
b
w
h
K
K
K ?
?Case (III) W. A. + W. B. (CH
3
COO NH
4
)
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
NH
4
+
+ H
2
O NH
4
OH + H
+
_______________________________________________________
CH
3
COO
–
+ NH
4
+
+ 2 H
2
O NH
4
OH + CH
3
COOH + H
+
+ OH
–
_______________________________________________________
?
] [NH ] COO [CH
COOH] [CH OH] [NH
K
4
–
3
3 4
h
?
?
?
] [H ] COO [CH
] [H ] [OH COOH] [CH
] [OH ] [NH
OH] [NH
K
–
3
–
3
–
4
4
h
?
?
?
?
?
b a
w
h
K . K
K
K ?
? pH calculation
?Case (I) : W. A. + S. B. (CH
3
COONa ? c, K
a
) , h ? degree of hydrolysis.
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
c 0 0
c (1 – h) ch ch
?
h – 1
ch
h) – (1 c
(ch)
K
2 2
h
? ?
h < < 1 ? K
h
= ch
2
?
c
K
h
h
?
?
a
w
h
–
K
K
c. K c. h c ] [OH ? ? ? ? ?
c] log – pK – [pK
2
1
pOH
a w
?
?
c] log pK [pK
2
1
pH
a w
? ? ?
?Case (II) :S. A. + W. B. (NH
4
Cl ? c, K
b
)
NH
4
+
+ H
2
O NH
4
OH + H
+
c 0 0
c (1 – h) ch ch
?
h – 1
ch
K
2
h
? h < < 1 ? K
h
= ch
2
?
c
K
h
h
?
?
K
K
c K c c.h ] [H
b
w
h
? ? ? ? ?
?
?
c] log – pK – [pK
2
1
pH
b w
?
? p
OH
=
? ? c log p p
2
1
b w
k k
? ?
?Case (III) W. A. + W. B. (CH
3
COONH
4
? K
a
, K
b
, c)
CH
3
COO
–
+ NH
4
+
+ H
2
O NH
4
OH + CH
3
COOH
c c
c (1 – h) c (1 – h) ch ch
?
2
2
2 2
2 2
h
) h – 1 (
h
h) – (1 c
h c
K ? ?
? K
h
= h
2
1 h – 1 ?
?
h
K h ?
?
b a
w
K K
K
h ?
- - - - - (1)
? CH
3
COOH CH
3
COO
–
+ H
+
?
COOH] [CH
] COO [CH ] [H
K
3
–
3
a
?
?
?
] COO [CH
COOH] [CH
K ] [H
–
3
3
a
?
?
?
h) – (1 c
ch
K
a
? ?
(h < < 1) ? [H
+
] = K
a
. h ?
1) (from
K . K
K
. K ] [H
b a
w
a
?
?
?
K
K
. K
] [H
b
a
w
?
?
?
] pK – pK [pK
2
1
H p
b a w
? ?
? If , K
a
> K
b
? pK
a
< pK
b
? acidic,
K
a
= K
b
? neutral, K
a
< K
b
? basic
? Summary of hydrolysis
1. W. A. + S. B.
c] log pK [pK
2
1
pH
K
K
K
a w
a
w
h
? ? ? ?
2. W. B. + S. A.
c] log – pK – [pK
2
1
pH
K
K
K
b w
b
w
h
? ?
3. W. A. + W. B.
] pK – pK [pK
2
1
pH
K . K
K
K
b a w
b a
w
h
? ? ?
? Hydrolysis of salt of polyprotic acid / base (Na
2
CO
3
)
?
– 2
3
CO + H
2
O
–
3
HCO + OH
–
2
1
a
w – –
3 h
K
K
) (CO K ?
a
a – x x – y x + y
?
?
x x
?
–
3
HCO + H
2
O H
2
CO
3
+ OH
–
1
2
a
w –
3 h
K
K
) (HCO K ?
x – y y x + y
?
?
?
x y x
2 1
a a
K K ? ?
?
K K
h h
2 1
? ?
? Mainly hydrolysis is governed by
– 2
3
CO .
? ?
2
1
a
w
h
–
K
K
c
K c ] [OH
?
? ? ?
, ? ?
1
a
w – –
3
K
K
c
] [OH ] [HCO
?
? ?
, ? ? ?
x
y x
K
K
1
a
w
?
?
? ?
1
a
w
3 2
K
K
] CO [H ?
Page 5
Salt Hydrolysis
Acid + Base ? ? ? Salt + H
2
O neutralization
Salt + H
2
O ? ? ? Acid + Base ? ? ? reverse of neutralization ? Salt hydrolysis
since salt hydrolysis is an endothermic reaction hence on increasing the temperature, the extent
of hydrolysis increases.
? Types of salt
Case I Case II Case III Case IV
W. A + S. B S. A. + W. B. W. A + W. B. S. A. + S. B.
e.g. CH
3
COONa e.g. NH
4
Cl e.g. CH
3
COONH
4
e.g. NaCl
?Case : (I) Hydrolysis of WA + SB :
CH
3
COONa
? ? ?
CH
3
COO
–
+ Na
+
? spectator ion
?
?
Very strong Very weak
Conjugate base Conjugate acid
H – OH
CH
3
COOH NaOH
CH
3
COO
–
+ H
+
Na
+
+ OH
–
CH
3
COONa CH
3
COO
–
+ Na
+
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
__________________________________________
CH
3
COONa + H
2
O CH
3
COOH + Na
+
+ OH
–
__________________________________________________________________________
Note : (1) Only weaker part of salt undergoes hydrolysis. (2) This solution becomes basic.
?Case : (II) S.A. + W.B. (NH
4
Cl) :
NH
4
+
+ H
2
O NH
4
OH + H
+
, This solution becomes acidic
?Case : (III) W.A. + W.B. (CH
3
COONH
4
)
:
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
a x
a – x
NH
4
+
+ H
2
O NH
4
OH + H
+
a y
a – y
Can be acidic, basic or neutral
? acidic K K
b a
? ? neutral K K
b a
? ? basic K K
b a
? ?
?Case : (IV) S. A + S. B (NaCl) :
? No hydrolysis ? Solution will be neutral
? Relationship between K
a
, K
b
, and K
h
?Case (I) : W. A. + S.B. (CH
3
COONa)
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
] [OH COOH] [CH
K
–
–
–
3
?
?
? ?
K
K ?
?Case (II) : S. A. + W. B. (NH
4
OH)
NH
4
+
+ H
2
O NH
4
OH + H
+
?
] [NH
] [H OH] [NH
K
4
4
h
?
?
?
?
] [OH ] [NH
] [OH ] [H OH] [NH
K
–
4
–
4
h
?
?
?
?
?
?
b
w
h
K
K
K ?
?Case (III) W. A. + W. B. (CH
3
COO NH
4
)
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
NH
4
+
+ H
2
O NH
4
OH + H
+
_______________________________________________________
CH
3
COO
–
+ NH
4
+
+ 2 H
2
O NH
4
OH + CH
3
COOH + H
+
+ OH
–
_______________________________________________________
?
] [NH ] COO [CH
COOH] [CH OH] [NH
K
4
–
3
3 4
h
?
?
?
] [H ] COO [CH
] [H ] [OH COOH] [CH
] [OH ] [NH
OH] [NH
K
–
3
–
3
–
4
4
h
?
?
?
?
?
b a
w
h
K . K
K
K ?
? pH calculation
?Case (I) : W. A. + S. B. (CH
3
COONa ? c, K
a
) , h ? degree of hydrolysis.
CH
3
COO
–
+ H
2
O CH
3
COOH + OH
–
c 0 0
c (1 – h) ch ch
?
h – 1
ch
h) – (1 c
(ch)
K
2 2
h
? ?
h < < 1 ? K
h
= ch
2
?
c
K
h
h
?
?
a
w
h
–
K
K
c. K c. h c ] [OH ? ? ? ? ?
c] log – pK – [pK
2
1
pOH
a w
?
?
c] log pK [pK
2
1
pH
a w
? ? ?
?Case (II) :S. A. + W. B. (NH
4
Cl ? c, K
b
)
NH
4
+
+ H
2
O NH
4
OH + H
+
c 0 0
c (1 – h) ch ch
?
h – 1
ch
K
2
h
? h < < 1 ? K
h
= ch
2
?
c
K
h
h
?
?
K
K
c K c c.h ] [H
b
w
h
? ? ? ? ?
?
?
c] log – pK – [pK
2
1
pH
b w
?
? p
OH
=
? ? c log p p
2
1
b w
k k
? ?
?Case (III) W. A. + W. B. (CH
3
COONH
4
? K
a
, K
b
, c)
CH
3
COO
–
+ NH
4
+
+ H
2
O NH
4
OH + CH
3
COOH
c c
c (1 – h) c (1 – h) ch ch
?
2
2
2 2
2 2
h
) h – 1 (
h
h) – (1 c
h c
K ? ?
? K
h
= h
2
1 h – 1 ?
?
h
K h ?
?
b a
w
K K
K
h ?
- - - - - (1)
? CH
3
COOH CH
3
COO
–
+ H
+
?
COOH] [CH
] COO [CH ] [H
K
3
–
3
a
?
?
?
] COO [CH
COOH] [CH
K ] [H
–
3
3
a
?
?
?
h) – (1 c
ch
K
a
? ?
(h < < 1) ? [H
+
] = K
a
. h ?
1) (from
K . K
K
. K ] [H
b a
w
a
?
?
?
K
K
. K
] [H
b
a
w
?
?
?
] pK – pK [pK
2
1
H p
b a w
? ?
? If , K
a
> K
b
? pK
a
< pK
b
? acidic,
K
a
= K
b
? neutral, K
a
< K
b
? basic
? Summary of hydrolysis
1. W. A. + S. B.
c] log pK [pK
2
1
pH
K
K
K
a w
a
w
h
? ? ? ?
2. W. B. + S. A.
c] log – pK – [pK
2
1
pH
K
K
K
b w
b
w
h
? ?
3. W. A. + W. B.
] pK – pK [pK
2
1
pH
K . K
K
K
b a w
b a
w
h
? ? ?
? Hydrolysis of salt of polyprotic acid / base (Na
2
CO
3
)
?
– 2
3
CO + H
2
O
–
3
HCO + OH
–
2
1
a
w – –
3 h
K
K
) (CO K ?
a
a – x x – y x + y
?
?
x x
?
–
3
HCO + H
2
O H
2
CO
3
+ OH
–
1
2
a
w –
3 h
K
K
) (HCO K ?
x – y y x + y
?
?
?
x y x
2 1
a a
K K ? ?
?
K K
h h
2 1
? ?
? Mainly hydrolysis is governed by
– 2
3
CO .
? ?
2
1
a
w
h
–
K
K
c
K c ] [OH
?
? ? ?
, ? ?
1
a
w – –
3
K
K
c
] [OH ] [HCO
?
? ?
, ? ? ?
x
y x
K
K
1
a
w
?
?
? ?
1
a
w
3 2
K
K
] CO [H ?
? Solubility of sparingly soluble salt
(aq.) AgCl (s) AgCl
Solubility
? ? ? ? ? (aq) Cl (aq) Ag
–
?
?
? In ionic equilibrium all the components of equilibrium should be in same phase.
? In case of solubility equilibrium of sparingly soluble salt equilibrium is a heterogeneous equilibrium.
?Example (1) : Solubility of AgCl
AgCl (s) Ag
+
(aq) + Cl
–
(aq)
[AgCl]
] [Cl ] [Ag
K
–
eq
?
?
? K
sp
= K
eq
. [AgCl] = [Ag
+
] [Cl
–
]
?
It is a endothermic reaction on increasing temperature T
?
? solubility
?
?
?
?
?
?
?
? ?
?
2 1 sp
sp
T
1
–
T
1
R 2.303
H
K
K
log
1
2
?Example (2) : Solubility of Ag
2
CO
3
Ag
2
CO
3
(s) 2 Ag
+
+
– 2
3
CO
? ] [CO ] [Ag K
– 2
3
2
sp
?
? , ? In general , if salt is M
x
N
y
type, M
x
N
y
x M
y+
+ y N
x–
?
y – x x y
sp
] [N ] [M K
?
?
let , Q = [M
y+
]
x
[N
x–
]
y
Q = ionic product
If , Q = K
sp
? Equilibrium (Saturated solution) Q > K
sp
? PPt (Super saturated)
Q < K
sp
? Unsaturated solution.
? Various case in solubility
? Case (1) : Ag
2
SO
4
(S = 10
–3
mol/L)
Ag
2
SO
4
2 Ag
+
+ SO
– 2
4
S 0 0
0 2 S S K
sp
= [Ag
+
]
2
[SO
4
- -
] = (2 S)
2
(S) = 4 S
3
= 4 × (10
–3
)
3
? Case (2) : S (moL / L)
? ? ?
S (gm / L)
10
–3
4 2
SO Ag
S
(gm/L) = 10
–3
× (108 × 2 + 96)
? Case (3) : K
sp
given , Solubility = ?
Ag
2
SO
4
2 Ag
+
+
– 2
4
SO
S 0 0
0 2 S S
Read More