文档介绍：Chapter 6 Electrochemical Analysis
Anode reaction:
Red === Ox + ne -
Cathode reaction:
Ox + ne - === Red
Introduction
Oxidation – reduction reaction
Cell reaction expression
Anodesolution,(Ox)solution, (Red) Cathode
(6r-1)
(6r-2)
For example:
Zn ZnSO4,(xMol) CuSO4, (yMol) Cu
Anode: Zn Zn2+ + 2e-
Cathode: Cu2 + + 2e- Cu
(6r-3)
(6r-4)
2. Half-cell Potential
For half – cell reaction :
rAred pAOx + ne -
Nernst equation:
For a Cell:
Ecell = Ecathode - Eanode
If, Ecell > 0: Primary Cell
Ecell < 0: Electrolyic Cell
(6r-5)
(6-1)
(6-2)
Types of Electrodes
A metal in Equilibrium with its ions
(Class Ⅰelectrodes)
Ag+ + e- Ag
(6r-6)
(6-3)
A metal in equilibrium with a saturated solution of a slightly soluble salt (Class Ⅱelectrodes)
AgAgCl Cl -,(=1)
AgCl(s) + e- Ag + Cl –
Reference electrodes
Saturated calomel electrode (SCE)
HgHg2Cl2(s)Cl -,(sat’d KCL)
Hg2Cl2(s) + 2e- 2Hg + 2Cl –(sat’d KCL)
(6r-7)
(6r-8)
A metal in equilibrium with tow slightly soluble salts with mon Anion (Class Ⅲelectrodes)
AgAg2S,CdSAg+,Cd2+,S2-,
Ag2S(s) 2Ag++S2-
CdS(s) Cd2++S2-
(6r-9)
(6r-10)
4. The departure of potential
Liquid-junction potential
HCl() KCl(salt bridge, xM) KCl()
When x> Eljp<1mV
Polarization
Efact ≠ENernst and Csurf ≠Cbolk
Over-voltage
real potential start a reaction > equilibrium potential
Ohm drop
Ecell = Ecathode - Eanode + IR
R: resistance of solution, I: current
(6-4)
Potentiometry
Principle
(6-5)
(6-6)
(6-7)
(6-8)
2. Ion selective Membrane Electrode
Structure of ISE
Types
Fig 6-1