西北师范大学：《仪器分析》课程教学资源（PPT课件）Chapter 04 电位法 potentiometry

Potentiometric Methods These methods rely on the measurement of Ecell for quantification. A number of common reference and ion selective electrodes are reviewed along with general calculations and analytical approaches §4 Potentiometry

Potentiometric Methods These methods rely on the measurement of Ecell for quantification. A number of common reference and ion selective electrodes are reviewed along with general calculations and analytical approaches §4 Potentiometry

本章主要内容 • 电位分析法基本原理 • 离子选择性电极与膜电位 • 离子选择性电极的选择性 • 离子选择性电极的种类与性能 • 测定离子活（浓）度的方法 • 电位滴定法 • 重点掌握电位分析法的基本原理，掌握溶液pH值 的计算方法、运用工作曲线法和标准加入法进行 离子活度的计算

本章主要内容 • 电位分析法基本原理 • 离子选择性电极与膜电位 • 离子选择性电极的选择性 • 离子选择性电极的种类与性能 • 测定离子活（浓）度的方法 • 电位滴定法 • 重点掌握电位分析法的基本原理，掌握溶液pH值 的计算方法、运用工作曲线法和标准加入法进行 离子活度的计算

Classification of electroanalytical methods • Based on the quantitative relationship between some physical chemical properties of the chemical cell and concentration of the solute • Use the mutation of the physical chemical properties as indicating method of a titration reaction end-point, that is, electrical volumetry • Transfer the analyte into solid state (metal or oxide), then weigh mass of these metal or oxide deposited to ascertain amount of the analyte, that is electro￾gravimetry

Classification of electroanalytical methods • Based on the quantitative relationship between some physical chemical properties of the chemical cell and concentration of the solute • Use the mutation of the physical chemical properties as indicating method of a titration reaction end-point, that is, electrical volumetry • Transfer the analyte into solid state (metal or oxide), then weigh mass of these metal or oxide deposited to ascertain amount of the analyte, that is electro￾gravimetry

Classification of electroanalytical methods

Classification of electroanalytical methods

§4-2 Principle of potentiometry • 电位分析法的实质是通过在零电流条 件下测定两电极间的电位差(即所构成 原电他的电动势) 进行分析测定。包括 电位测定法和电位滴定法。 Theoretical basis of potentiometric analysis is Nernst equation: E = EOx/Red + ln RT nF aOx aRed For metal base electrode, aRed = 1, hence, E = EM n+/M + ln RT nF aM n+

§4-2 Principle of potentiometry • 电位分析法的实质是通过在零电流条 件下测定两电极间的电位差(即所构成 原电他的电动势) 进行分析测定。包括 电位测定法和电位滴定法。 Theoretical basis of potentiometric analysis is Nernst equation: E = EOx/Red + ln RT nF aOx aRed For metal base electrode, aRed = 1, hence, E = EM n+/M + ln RT nF aM n+

实际测量时，都是通过测定由 indicating electrode 和 reference electrode 组成的Cell 的电动势（electromotive force）来完成的。 Reference electrodes 通常由以下几种电极来充当 ，它们的电位在 一定条件下是恒定的，与待测离子浓度无关。 甘汞电极 Ag/AgCl电极 氢电极 pH玻璃电极 Setup of potentiometric methods Frame of reference electrodes in common use (滞后作用，磁滞现象）)

实际测量时，都是通过测定由 indicating electrode 和 reference electrode 组成的Cell 的电动势（electromotive force）来完成的。 Reference electrodes 通常由以下几种电极来充当 ，它们的电位在 一定条件下是恒定的，与待测离子浓度无关。 甘汞电极 Ag/AgCl电极 氢电极 pH玻璃电极 Setup of potentiometric methods Frame of reference electrodes in common use (滞后作用，磁滞现象）)

Cell Potential and Concentration Recall: 110oV Ecell =EcathodeEonode Salt teidge f .Anode is a reference Cu clectrode cell(constant potential) 00100 M 0.0100M .Temp is 298K ZnSO CuSO Assume activities and 7atr)-2nor)+2e Cu(ag)2e-Cul “2+=0010 concentrations are same 4.m0010 Cathode Then:Ecell=Ecathode+(0.0592/n)Log[Ox]-Eref So,Ecell o Log[Ox]-Potentiometry(ISE)

Potentiometric methods Reference Indicating electrode electrode The part The part of of the cell the cell that that is held contains the constant solution we are interested in measuring

Saturated Calomel Electrode (SCE): HgHg2Cl2(sat'd),KCI(a=x M)l. Electrical lead Inner tube containing a paste of Hg.HgaClz. and saturated KCI Saturated KCl Small hole Fritted disk Ground (or a porous glass fiber) sleeve

Reference electrodes Calomel electrode (SCE) A much more common reference electrode. Hg Hg2C KCI// fiber Hg2Cl2/KCl Chloride is used to Hg maintain constant ionic strength. KCI solution asbestos fiber