Voltammetry and polarography
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第十三章 伏安和极谱法 Voltammetry and Polarography PowerPoint PPT Presentation


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第十三章 伏安和极谱法 Voltammetry and Polarography. 什么是伏安和极谱分析法 伏安和极谱分析法是根据测量特殊形式电解过程中的电流 ― 电位(电势)或电流 ― 时间曲线来进行分析的方法。是电分析化学的一个重要分支。. 在含义上,伏安法和极谱法是相同的,而两者的不同在于工作电极: ―― 伏安法的工作电极是电解过程中表面不能更新的固定液态或固态电极 ,如悬汞、汞膜、玻璃碳、铂电极等; ―― 极谱法的工作电极是表面能周期性更新的液态电极 ,即滴汞电极。(有的书把两者统称为极谱法).

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第十三章 伏安和极谱法 Voltammetry and Polarography

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Voltammetry and Polarography




1922Heyrovsky 1925


1959 20



102105molL1109 molL1

%



1.

(1)(Diffusion)

,.,.,


2.(convection)

,.,.:a.b..

3.(migrition)

,,.









,


c

c

x

x


i

x I

i =xciExuOici-Di(dci/dx)


=++=-D(dC/dX)VxCExU0C

-,(mol/cm2); D-(cm2/s);

Vx-(cm/s); Ex-x(/cm)

C-(mol/L); U0-(cm2/s.v)


O+e- =R

j

j=nFi=nFxcinFExuOici-nFDi(dci/dx)


KCl

ji=-n F D i(dci/dx)


Cix


i=A j =A nFDi (coi-csi)/

Coicsi A


csi

i= AnFDicoi/=K coi


i--t



=(Dt)1/2

i=(nF AD1/2i coi)/( 1/2t1/2)


  • t t33



1.

i=k (coi-csi)/


i=k (coi-csi)/

E3O


E0E3Sid

E 1/2


2.


i=k (coi-csi)/


1.



  • SCE


  • DME0.05mm35/


  • 0.51mm

    V= EEw+iR

    V=Ew(SCE)


  • DME

  • 1.32


  • DME

  • DME>0.4V(VS SCE)



110-3 molL1Cd2+ (0.1 molL1KNO3)


2.


  • i=ic+if

    Cd2+Cd2+


  • BDCd2+Cd2+ : Cd2++2e+Hg==Cd(Hg)

    : 2Hg-2e+2Cl-==Hg2Cl2


Cd2+Cd2+SCd2+0(co-cs)/Cd2+Cd2+i ( )


  • DE ECd2+DMECd2+DMECd2+Cd2+Cd2+


CSi=KsC0


E 1/2 DME


  • iE


  • CS

  • CS




--------

it =708nDqm2/3 t 1/6c

id

id =607nDqm2/3 t 1/6c

=6/7i


  • idn

-----

K=607nDqm2/3 t 1/6


h1cmid2%

  • qm2/3 t 1/6---

  • id h 1/2


I=607nD---InDI


  • nDid1.3%/,id1% 0.5


  • Dqmt




  • --O2 ,Cu2+,Fe3+





(1).

Faraday

if = id + im

Idim


250100





4.8


0.02%0.002%X--100



-- O28mgL-1,O2


  • O2--N2H2CO2H2CO2

  • Na2CO3O2

  • O2--Na2SO3,O2SO32-O2


  • --H+

  • -- E 1/2

  • --<0.2V


""


1

--

--.9,


--ssxCx


--

  • -- x(x)xsCxx+s


x(Cx)Vs(Cs),Hx,Hx+s,


  • --x(Cx),s(Cs)Hx+s,Hx+sVs ,Hx+sVs4.10 Vs




()

  • Nernst


  • Nernst


,


(2)



E 1/2 E 1/2 E 1/2 E 1/2


(3)




  • +


(1)


E 1/2E 1/2


Elg id-i/i0.059/nE 1/20.059/n


2



E 1/2


---CxE,E --lgCX,

  • n

  • n


(E 1/2)c(E 1/2)sK


npCxE1/2K

KCx


3

1.

2.

3.H+ E 1/2


4.

5.


1 i--E

  • --


  • 5mV/si--E


  • 250mV/Si--E


  • --767


  • --Pt

  • -- i-E



  • 1.

    ----JP--27S;

    ----


5S2S2S--


  • 2.E=E0-kt ( E) 0.5Vtk


i--tiRE-t


  • 3. EDMEi






  • 4.14


3.


VV/s Acm2


  • Ep

    Ep=E -1.1RT / nF

    = E -0.028 V/n

    56/ n mV,


4.

14080

20.0020.25


3

4


5.

1)

l10-5mol/L 1X10-7mol/L


,3.57V0.25ip/id=3.3n1/2ipid


2)

20050


3

5-10


1001000JP5000


4

257


di/dEdi/dtEd2i/dE2d2i/dt2E16-6


9.


10.


11.

K1K2


i-E ipEp ip Ep


1

  • 4.15


2


  • 4.16



4.


ipa=ipc

  • Epa=E +1.1RT / nF



----Epa Epc


Epa=E +1.1RT / nF

Epc=E -1.1RT / nF

Ep= Epa- Epc

=2.2RT / nF

=56.5/n (mV)


EpEp55/nmV65/nmV



Ep59/n mV

ipc/ipa11 4.17B


v Epc Epv4.17 C


5



1

23


2


3


  • 4 15


  • 225250Hz50mv4.19


  • 10-7-10-8 mol/L 4.20


  • icif t-1/2 icic


  • ic


  • 1960Barker2ms


icif


if20ms ic if


NPPDPP

  • --0V4060ms


20ms if 4.21


ilid67 E1/2


  • E5100 mv4080ms4.22(a)


20ms20ms4.22(b)i4.22(c)


i E1/2i


E 1/2,

E


Ep= E 1/2E/2

+"-"


ift-1/2

iCe-t


  • 108 mol/L106107 mol/L 10101011 mol/L

  • 25mV5000



Stripping Voltammetry

stripping voltammetry4.24D


4.24


0.8V Cu 2+, Pb 2+ , Cd 2+


4.25


1071011 mol/L



(1)


(2) 0.1mm0.1mm1.01.5mm



(3)


(4)




ip= -Kc----

ip= KnA/V


315min



l

A === B C

B + ne C E

2

A ne B E

BC==A C

3

A ne B E

B === C C

CEECREC


106108 mol/L109 mol/L 1010 mol/L


.








kk 45%/


0.1 mol/L1.2


5108 mol/L 104 mol/L


11010 mol/L


OrgH



OrgHOrgBHOrg


OrgHBHOrgH


II4-23





1

2

3


CdI4 2- Cd 2+


108mol/L


0.1


58


107109 mol/L



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