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) AgAgCl Cl - ,(=1) AgCl(s) + eAg + 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)
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) AgAg2S,CdSAg+ ,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<1mV 2) Polarization Efact ≠ENernst and Csurf ≠Cbolk 3) Over-voltage real potential start a reaction > 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