上海大学《仪器分析 - Instrumental Analysis》（英文版）_Chapter 6 Electrochemical Analysis

Chapter 6 Electrochemical Analysis

Chapter 6 Electrochemical Analysis

6.1 Introduction 1 Oxidation- reduction reaction Anode reaction Red =s Ox+ ne (6r-1) Cathode reaction Ox ne === Red (6r-2) Cell reaction expression Anode solution, (aox)II solution, (Red) Cathode

Anode reaction: Red === Ox + ne - Cathode reaction: Ox + ne - === Red 6.1 Introduction 1. Oxidation – reduction reaction Cell reaction expression Anodesolution,(Ox)solution, (Red) Cathode (6r-1) (6r-2)

For example: Zn ZnSO4,(xMol)I I CuSO4, (Mol)I Cu Anode:Zn、Zn2+2e (6r-3) Cathode: Cu2++ 2e Cu (6r-4)

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 Ared+ ne pAox (6r-5) Nernst equation E=E 0 +Rl In cox nF (6-1) red For a cell cells cathode E anode (6-2) If, Ecell >0: Primary Cell Ecell<0: Electrolyic Cell

2. Half-cell Potential For half – cell reaction : rAred + ne - pAOx Nernst equation: For a Cell: Ecell = Ecathode - Eanode If, Ecell > 0: Primary Cell Ecell < 0: Electrolyic Cell   r red p o x nF RT E E ln 0 = + (6r-5) (6-1) (6-2)

3. The Types of Electrodes 1)Ametal in Equilibrium with its ions (Class I electrodes Ag+e←Ag (6r-6) E E RT n a (6-3) g 8 Ag Ag

3.The Types of Electrodes 1) A metal in Equilibrium with its ions (Class Ⅰelectrodes) Ag+ + e￾Ag + = + + + F A g R T Ag Ag Ag E Ag E ln 0 (6r-6) (6-3)

2 A metal in equilibrium with a saturated solution of a slightly soluble salt (Class Electrodes) Ag AgCl Cl, (a-1) AgCl()+e+Ag Cl (6r-7) Reference electrodes Saturated calomel electrode (SCE) Hg Hg2Cl2(s)I,; (sat'd KCL) Hg2Cl2(s)+ 2e+ 2Hg 2CI(sat'd KCL)(6r-8)

2) A metal in equilibrium with a saturated solution of a slightly soluble salt (Class Ⅱelectrodes) AgAgCl Cl - ,(=1) AgCl(s) + e￾Ag + Cl – Reference electrodes Saturated calomel electrode (SCE) HgHg2Cl2(s)Cl - ,(sat’d KCL) Hg2Cl2(s) + 2e- 2Hg + 2Cl – (sat’d KCL) (6r-7) (6r-8)

3 A metal in equilibrium with tow slightly soluble salts with a common anion (Class Electrodes) Ag Ag2 S, CdS Ag+, Cd2+S 92S(5)-2Ag*+s (6r-9) CdS Cd2++S2 6r-10

3) A metal in equilibrium with tow slightly soluble salts with a common Anion (Class Ⅲelectrodes) AgAg2S,CdSAg+ ,Cd2+,S2- , Ag2S(s) 2Ag++S2- CdS(s) Cd2++S2- (6r-9) (6r-10)

4. The departure of potential HCI(0.1M)I KCl(salt bridge, XM) KCI(0. 1M) When x>3.6 Elin<lmV olarization Fact ENernst and surf ≠Cbok er-voltage real potential start a reaction equilibrium potential Ohm drop ell"Cathode" anode +|R (6-4) R: resistance of solution, I: current

4. The departure of potential 1) Liquid-junction potential HCl(0.1M) KCl(salt bridge, xM) KCl(0.1M) When x>3.6 Eljp equilibrium potential 4) Ohm drop Ecell = Ecathode - Eanode + IR R: resistance of solution, I: current (6-4)

6.2 Potentiometry 1. Principle E E rer +E (6-5) =0 RIn 6-6) re IndiGo indi n Ox (6-7) cellSo E d +rtIn a-e+e Ox EU. hn a rel Ox constant +n a Ox (6-8)

6.2 Potentiometry 1. Principle Ecell = Eindi − Eref + ELJ   red o x n f RT Eindi Eindi ln 0 = + nf ox RT Eindi Eindi ln 0 = + cons t n o x n f o x R T indi ref LJ n f o x ref Lj R T cell indi E E E E E E E E    lg ln ln 0.0591 tan 0 0 = + = − + + = + − + (6-5) (6-6) (6-7) (6-8)

2 on selective Membrane electrode Structure of ise Electrode wire ion exchange liquid (inne refrence solution) inne refrence electrode ion selective membrane g 6 types Glass ISE Liquid pure Solid crystal mixture Non crystal

2. Ion selective Membrane Electrode • Structure of ISE • Types Fig 6-1