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This university is not simply turning out specialists, it is

preparing citizens. And citizens are not spectators in the

affairs of their country. They are participant in its future.

G. W. Bush, Address at Tsinghua University

Our Goals

(1) Calculate unknown potential from given potentials

(2) The principle for electroanalysis through potential

measurement;

(3) Construction and application of Pourbaix diagram.

2) influential factor of Ej

Pt(s), H2(g,p)HCl(m)HCl(m′)H2(g, p), Pt(s)

Ej

On passage of 1 mole of electrons through the cell, t+ mol H+ and t mol Cl pass the boundary

-+

+ -

ClH

H Cl

'ln ln

'j j

aaG t RT t RT nFE

a a

For uni-univalence electrolytes

'ln)12(

'ln)(

m

m

F

RTt

m

m

F

RTttE j

4) requirements of salt bridge electrolyte1) does not react with either solution2) transference number of cation and anion is close3) of high concentration.

ions K+ NH4+ Cl NO3

102 /S·m2·mol-1 0.7352 0.734 0.7634 0.7144

t+ of some common salt bridge electrolytes

c/mol·dm-3 0.01 0.05 0.10 0.20

KCl 0.490 0.490 0.490 0.489

NH4Cl 0.491 0.491 0.491 0.491

KNO3 0.508 0.509 0.510 0.512

m

c/mol·dm-3 0 0.2 1.0 2.5 3.5

Ej 28.2 19.95 8.4 3.4 1.1

Concentration-dependence of Ej

Why does salt bridge reduce the junction potential.

+ + + + +- - - - -

5) Effects of salt bridge:

6) Elimination of junction potential

Chapter 7 Electrochemistry

§7.9 Electrode potential and electromotive forces

1) emf’s and rGm of a reaction in different forms

reaction:

H2 + Cu2+ Cu + 2H+ G1, E1

1/2 H2 + 1/2 Cu2+ 1/2 Cu + H+ G2, E2

Cu + 2H+ H2 + Cu2+ G3, E3

7.9.1. Influential factors of electrode potential

Exercise: Compare G1, G2, G3 and E1, E2, E3.

2) between different oxidation states

Fe3+ Fe2+ Fe1y

2y

3y

Give the relationship between

Exercise

Initial state and final state

AgCl = Ag+ + Cl-

Ag(s)|AgNO3(c1) ||KCl(c2) |AgCl(s)|Ag(s)

3) of relevant electrodes + AgCl/AgAg /Ag y y

+AgCl/Ag Ag /AgE y y y

splnRT

E KnF

y y

+AgCl/Ag spAg /Agln

RTK

nF y y y

-2Ag(CN) /Ag

y+Ag /Ag

y

Exercise:

deduce the relationship between

and

7.9.2. Concentration-dependence of

Nernst equation ox

red

lnaRT

nF a y

for Ag+/Ag electrode

+ + +Ag /Ag Ag /Ag Ag Ag /Ag Ag

0.05916ln ln

RTa a

nF n y y

(Ag+/Ag) depends on [Ag+] , or (Ag+/Ag) responds to [Ag+].

The relationship between (Ag+/Ag) and [Ag+] can be used

for quantitative electroanalysis of Ag+.

Can we use hydrogen

electrode for measuring the

pH of the solution?

Give the principle of the

measurement.

Exercise:

why electrode Hg(l)Hg2SO4(s)CaSO4(s)Ca2+(m) can be used to measure the concentration of Ca2+ in a solution?

Normal and italic

7.9.3. pH-dependence of : Pourbaix diagram

For electrode reaction with H+ or OH- participating in, the electrode potential will depend on pH.

O2 + 4H+ + 4e- 2H2O

= ⊖ + 0.05916 lgaH+

= 1.229 - 0.05916 pH

= ⊖ + 0.05916 lgaH+

= 0.000 - 0.05916 pH

2H+ + 2e- H2

pH-potential diagram/Pourbaix diagram

H2O

O2

H2

pH

/ V

2 4 6 8 10 12 14

0.401

-0.828

0.000

1.229

0

Marcel Pourbaix, “Atlas of electrochemical equilibria in aqueous solutions”, National Association of Corrosion Engineers, 1974.

Marcel Pourbaix (1904–1998), a Russian-born, Belgian chemist.

Construction of Pourbaix diagram

Cu2+ Cu(OH)2

Cu

pH

/ V

2 4 6 8 10 12 140

CuO22

Cu2O

Group discussion -2

1) How can you measure the liquid-liquid junction potential of a HCl/KCl interface? Write out the notation of the cell you use to conduct your measurement.

2) A potential is usually established across the cell membrane due to the concentration difference of K+ inside and outside a cell, which is named as membrane potential. This potential is crucial for sensation of any living thing. Can you design an experimental apparatus for measuring the membrane potential of a cell? State the principle you use.