Transcript WATER AND SOLUTIONS

SOLUTIONS OF
ELECTROLYTES
Electrolysis
Battery
Electrons
Ohm’s law
+ Anode (+)
oxidation
Cathode (-)
reduction
E  volts 
I  
R   
Charge  current, I  time, t
1 coul = 3x109 esu
Cations
+
Anions
Electrolytic cell
transference number
I
I
t 
t 
I
I
t  t  1
Faraday’s Laws
The passage of 96,500 coulombs (= F) of
electricity through a conductivity cell produces a
chemical change of 1 gram equivalent weight of
any substance
Charge of electron:
1 gram equivalent 6.1023 charges
e=96500/ 6.1023 =1.6x10-19 coul/electron
=4.8x10-10 esu/electon
Theory of Electrolytic
Dissociation
+ Electrolyte
+
- +
- +
- +
Polar solvent
+
+ - + - +
+
+
+
- + - + +
-
Arrhenius Theory:
Strong electrolytes
H2O + Na+Cl- = Na+ + Cl- + H2O
H2O + HCl = H3O+ + ClWeak electrolytes
H2O + CH3COOH = H3O+ + CH3COO-
Ionization Degree
AB = A+ + B = [A+ ]/[AB]o = [B-]/[AB]o
[AB]o = [A+ ] + [AB]
Strong electrolytes:
Weak electrolytes:
  0.3
 < 0.3
Weak Electrolytes
[A  ]

[AB]o
AB = A+ + B[AB]o  [AB]  [A  ]
(  1)
[AB]  [AB]o  [A  ]
[A  ]  [B ]
Kd

[ A  ][ B ]
[ AB]

[ A  ]2
[ AB] [ A  ]
o

 2 [ AB]
1
o
K d (1   )
Kd


[AB]o
[AB]o
Colligative Properties
T f  i  K f  csolute
Tb  i  Kb  csolute
  i  RT  csolute
o
psolvent  i  psolvent
 xsolute
i  2 for NaCl and CaSO4
i  3 for CaCl2 and K2SO4
i  4 for FeCl3 and K3Fe(CN)6
Strong Electrolytes
+ -
+
+
-
Ion “atmosphere”
+
-
-
-
+
-
-
+
+
+
+
+
+
+
+
Debye-Huckel Theory
- - + - Ionic Strength
+ + +
+ ++ +
+ +
log    
Az  z 
1  ai B 
1  2 1  2 1 j
  [A ]  z  [B ]  z   ci zi2
2
2
21
Low concentration of electrolyte
High concentration of electrolyte
log     Az z 
log    
Az  z
ai B
Solubility Product
AgClsolid
= Ag+
+
Cl-
[ Ag  ]  [Cl  ]
K
[AB]solid
[ Ag  ]  [Cl  ]  K sp
• What is the solubility of silver chromate (s, M) in
aqueous solution containing 0.04M silver nitrate ?
Ag2CrO4 = 2Ag+ + CrO42-
Ksp = 2x10-12 (Reference literature)
Ksp = [Ag+]2[CrO42-] = (2s + 0.04)2.s
s = [Ag2CrO4]  2 x 10-12/1.6 x 10-3 = 1.25 x 10-9 M
Effect of Ionic Strength
on Solubility
AgClsolid = Ag+ + Cl-
Ksp = aAg+.aCl- = +[Ag+]. -[Cl-]
[Ag+].[Cl-] = Ksp /2
• Calculate solubility of silver chloride (s, M) in 0.1M
ammonium sulfate. Ionic strength of 0.1 M (NH4)2SO4 =
0.3; activity coefficient = 0.7.
AgCl = Ag+ + Cl-
Ksp = 1.76x10-10 (Reference literature)
s2 = Ksp /2
s = (1.76 x 10-10)1/2/0.7 = 1.9 x 10-5 M