Electrochemistry-3.ppt

Electrochemistry(3)
Xuan Cheng
Xiamen University
Physical Chemistry
1
Physical Chemistry
Electrolytic Conductivity
Electrochemistry
The electric current I
()*
()*
The electric current density j
The conductivity 
The reciprocal of conductivity (resistivity) 
()*
()*
2
Physical Chemistry
Electrolytic Conductivity
The resistance R
()*
()
The conductance G
1 S=1 -1
Siemens

ohm
-1
mho
Electrochemistry
3
Physical Chemistry
Molar Conductivity
The conductivity of a solution
depends on the number of ions present
The molar conductivity m
Electrochemistry
()*
The electrolyte’s stoichiometric molar concentration
4
Physical Chemistry
H2SO4
KOH
KCl
MgSO4
CH3COOH
0
15
5
10
c/(moldm-3)
20
40
60
80
Conductivity vs. concentration
k/(Sm-1)
0
 vs. c
Strong electrolytes
Fully ionized in solution: ionic solids, strong acids and bases
The concentration of ions is proportional to the concentration of electrolyte added
Weak electrolytes
MgSO4
CH3COOH
Neutral electrolytes
KCl
H2SO4
KOH
Molar Conductivity
Electrochemistry
()*
5
演示
6
400
300
200
100
m/(Scm2 mol-1)
HCl
NaOH
AgNO3
CH3COOH
0
In an extensive series of measurements during 19th century, Friedrich Kohlrausch
At low concentrations
The infinite-dilute molar conductivity
The infinite-dilute molar conductivity of the cations and anions
Law of the independent migration of ions
Molar Conductivity
Physical Chemistry
The limiting molar conductivity
Electrochemistry
7
演示
8
摩尔电导率与浓度的关系
由于溶液中导电物质的量已给定,都为1mol,所以,当浓度降低时,粒子之间相互作用减弱,正、负离子迁移速率加快,溶液的摩尔电导率必定升高。但不同的电解质,摩尔电导率随浓度降低而升高的程度也大不相同。
9
Electrochemistry
10