每日一句 This university is not simply turning out specialists, it is preparing citizens. And...
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Transcript of 每日一句 This university is not simply turning out specialists, it is preparing citizens. And...
每日一句
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.
+ + + + +- - - - -
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.
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.