87.10 Application of EMF and electrode potential Levine pp.431-443 14.8 Concentration cell 14.9 Liquid-junction potential 14.10 Applications of eMF measurements 14.12 ion-selective membrane electrodes
§7.10 Application of EMF and electrode potential Levine pp. 431--443 14.8 Concentration cell 14.9 Liquid-junction potential 14.10 Applications of EMF measurements 14.12 ion-selective membrane electrodes
87.10 Application of EMF and electrode potential 7.10.1 Computation of emf E 9+- For cell with single solution For cell with two electrolytic solutions: Zn(s)Znso(m,)CusO(m,) Cu(s) Cd(s)ICdso(a+)Hg SO4(s)IHg() RT e=O-=E+-In E 9-9 RT RT In RT m,y O4 o+Ina E=e+-In nF RT )-In a nF The mean activity coefficient(r+) has to be used in stead of the activity coefficient of individual ion(2 or r)
7.10.1 Computation of emf For cell with single solution: Cd(s)|CdSO4 (a±) |Hg2SO4 (s)|Hg(l) 2 2 SO Cd 4 2 ln ln ( ) ln E RT RT a a nF nF RT a nF − + + − + − + − = − = − − + = − − E = − + − For cell with two electrolytic solutions: Zn(s)|ZnSO4 (m1 ) ||CuSO4 (m1 ) |Cu(s) 2 2 Cu Zn ln RT a E E nF a + + = − = + + − 1 ,1 2 ,2 ln RT m E E nF m = + The mean activity coefficient ( ) has to be used in stead of the activity coefficient of individual ion (+ or - ). §7.10 Application of EMF and electrode potential
87. 10 Application of EMF and electrode potential 7.10.2. Judge the strength of the oxidation and reduction 酸性溶液数据 电对符号 电极反应 电极电势E P(Fe+/Fe2t)=0.771 v 2+2H"+2e=-2HN3(ag) 333 ge(L2=0.5362V Cs+/Cs Cs"+e=Cs Rb+/Rb Rb+e=Rb -298 K'+e=K Ba2+/Ba Oxidative form: Fe3 Ba2+2e=Ba 292 512 Sr+2e'=Sr -2894 Ca2+/ Ca Ca+2e=Ca Reductive form: fe2+ I Mg2+Mg 4g+2e=Mg 372 Ce+3e=Ce Bro +H,0+2e =Br+20 Which is stronger oxidative reagent, Fe+ or I2? 1o+HO+2=C+20H Br7+/Br5+ BrOa+H,0+2e=BrO+20H HXe063"+2H,0+2e=HXeO:+40H Which is stronger reductive reagent. Fez+ or I-? C14+/CL I Clo ( ag)+e=CIO, 00001 LRus C14+Cl CIO:(g)+e'=CIO2 Why?E>0 criterion [x6+x 4:09 oyg)+HQ+26=02+20H 124 https://wenku.baiducom/view/7d51ac34caaedd3382c4d32b.html
7.10.2. Judge the strength of the oxidation and reduction ⊖ (Fe3+ /Fe2+ ) = 0.771 V ⊖ (I2 /I− ) = 0.5362 V Oxidative form: Fe3+, I2 Reductive form: Fe2+, IWhich is stronger oxidative reagent, Fe3+ or I2 ? Which is stronger reductive reagent, Fe2+ or I −? Why? E > 0 criterion https://wenku.baidu.com/view/7d51ac34caaedd3382c4d32b.html §7.10 Application of EMF and electrode potential
87. 10 Application of EMF and electrode potential 7.10.3 Determination of the reaction direction ∠G≤0LG=-HFE When concentration differs far from the standard concentration, should be used in ge(Fe3/Fe2)=0771V; stead of ge(L2r)=0.5362V au tle= au 1.7V Stronger oxidizing species oxidizes stronger reducing species to produce O+2HO+4e=40Hp=0401 weaker reducing and weaker How can we make au in mine dissolve in OXidizing species alkaline solution?
7.10.3 Determination of the reaction direction When concentration differs far from the standard concentration, should be used in stead of ⊖. Stronger oxidizing species oxidizes stronger reducing species to produce weaker reducing and weaker oxidizing species. ⊖ (Fe3+/Fe2+) = 0.771 V; ⊖ (I2 /I− ) = 0.5362 V + Au 1e Au − + = =1.7 V O +2H O+4e 4OH 2 2 − − = =0.401 How can we make Au in mine dissolve in alkaline solution? §7.10 Application of EMF and electrode potential G 0 G nFE = −
87. 10 Application of EMF and electrode potential 7.10.3 Determination of the reaction direction 北京矿冶研究总院 黄金提取的发展过程 氰化法: 金可嵱于氰化物嵱漩,是西方炼金术士在18世纪发现的,19世纪 80年代,氰化法的研究取得了进畏。1886年,F,以.和W福雷斯特 Forrest)兄弟发明了用浓氰化钾液浸出矿石中的金,并用锋块从浸 液中置换沉汶金的方法。1890年,氰化法正式引进南非,这种简便的 浸出方法使南非黄金生产摆脱了因境,而立即被各厂家广泛采用。 SSH 氰化法在湿法冶金史上树立了一个重要里程碑,而成为现代湿法 提金的最重要方法,是黄金提取的一场革命 世界黄金产量的75%左右是采用氰化提金技术获得的。虽然氰化 物有剧毒,但目前还没有一种适宜的濙金嵱剂能够代替,氰化提金工 艺至今以及未来几十年内,在黄金生产领城仍将占居主导地位
7.10.3 Determination of the reaction direction §7.10 Application of EMF and electrode potential
87.10 Application of EMF and electrode potential 7.10.3 Determination of the reaction direction Application of Pourbaix diagram Corrosion with hydrogen evolution Corrosion with oxygen absorption > Passivation? 1.5 C Cu(oh Surface conversion? 1.0 CuO, 2 Electrochemical synthesis? 0.5 CuO 0.0 Cu 02468101214
Application of Pourbaix diagram Cu2+ Cu(OH)2 Cu pH / V 0 2 4 6 8 10 12 14 CuO2 2− Cu2O 0.0 0.5 1.0 1.5 7.10.3 Determination of the reaction direction Corrosion with hydrogen evolution Corrosion with oxygen absorption Passivation? Surface conversion? Electrochemical synthesis? §7.10 Application of EMF and electrode potential
87.10 Application of EMF and electrode potential 7.10.3 Determination of the reaction direction Divergent /Disproportionation reaction CL 2Nacl= Na Cl+ Nacio+ho HIO→1O3+12 which species can undergo divergent reaction 1.16 0.50 CIo Hs :r cIo 033Co 136 Divergent reaction occur when PR>P 0.50 0.89 元素电势图( Latimer diagram) Q=o(HOl2)=+145V 92=(O3/HO=+113V Can what species undergo divergent reaction?
Divergent /Disproportionation reaction Cl2 + 2NaCl = NaCl + NaClO + H2O Divergent reaction occur when R > L HIO → IO3 − + I2 R 2 L 3 (HIO/I ) 1.45V (IO /HIO) 1.13V − = = + = = + which species can undergo divergent reaction? 7.10.3 Determination of the reaction direction Can what species undergo divergent reaction? 元素电势图（Latimer diagram） §7.10 Application of EMF and electrode potential
87.10 Application of EMF and electrode potential 7.10.4. Advance of reaction(equilibrium constants) ∠G=0 At equilibrium ∠G=-nFE o(Fe”+/Fe2)=q(2/r) Fe3++I→>Fe2++%2I p(Fere)-p(12/)=7 T RTa o(Fe+/Fe2+)=e(Fe+/Fe2*)+In-Fe' nF RT, aF2 a, RT In K F nF (2I)=°(121,a1
7.10.4. Advance of reaction (equilibrium constants) 3 2 2 2 2 3 3 2 I Fe 2 I Fe Fe I Fe I (Fe / Fe ) (I / I ) ln ln ln ln a RT RT a a nF a nF a RT RT a a E K nF a a nF + − + + + − + + − − = − = = 3 2 3 2 3 2 Fe Fe (Fe / Fe ) (Fe / Fe ) ln RT a nF a + + + + + + = +2 I 2 2 I (I / I ) (I / I ) ln RT a nF a − − − = + 3 2 2 (Fe / Fe ) (I / I ) + + − = Fe3+ + I ¯→ Fe2+ + ½ I2 At equilibrium §7.10 Application of EMF and electrode potential G nFE = − G = 0
87.10 Application of EMF and electrode potential 7.10.4. Advance of reaction(equilibrium constants) Standard emf and standard equilibrium Four equilibria in solution constant D Dissolution equilibrium nFE RTIn K 2)Reaction equilibrium 3 ) Dissociation equilibrium RT E In K 4) Coordination equilibrium nF For any reaction that can be designed to Example Determine the solubility products of take place in an electrochemical cell, its Agcl(s) equilibrium constant can be measured AgCl(s)—Ag++Cl electrochemically
Standard emf and standard equilibrium constant ln = − = − r m G nFE RT K ln RT E K nF = For any reaction that can be designed to take place in an electrochemical cell, its equilibrium constant can be measured electrochemically. Four equilibria in solution 1) Dissolution equilibrium 2) Reaction equilibrium 3) Dissociation equilibrium 4) Coordination equilibrium 7.10.4. Advance of reaction (equilibrium constants) §7.10 Application of EMF and electrode potential Example Determine the solubility products of AgCl(s). AgCl(s) ⎯→Ag+ + Cl¯
87.10 Application of EMF and electrode potential 7. 10.5 Potentiometric titrations GElH*(m)ISCE Differential plot 0.700 HCI-NaOH 20.0030.0040.00 NaOH cI→ inflexion point 0.00 10.0020.00 0.0040.0050.00 automatic potential titrator
7.10.5 Potentiometric titrations GEH+ (mx )SCE automatic potential titrator §7.10 Application of EMF and electrode potential