Chapter 7 Electrochemistry

Chapter 7 Electrochemistry

§7.9 Electrode potential and electromotive forces

H2O

O2

H2

pH

/

V

2 4 6 8 10 12 14

0.401

-0.828

0.000

1.229

0

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 for 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

Application of Pourbaix diagram

Cu2+ Cu(OH)2

Cu

pH

/ V

2 4 6 8 10 12 140

CuO22

Cu2O

Pourbaix diagram of iron-water system

Equilibrium line

Stable zone

Fe2+

Fe2O3

Fe

pH

/ V

2 4 6 8 10 12 140

Fe3O4

Fe3+

FeO22

Stable state

Reaction

Product

Protection, passivation,

active dissolution,

electroplating,

electrosynthesis

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.