Transcript Slide 1

Handouts
• Syllabus
• Safety (detailed)
• Web page is up and running
Knowing Nernst:
Non-equilibrium copper redox chemistry
Safety / Waste disposal
• There will only be one liquid waste disposal
bottle (kept in the hood by the lab entrance),
since all reactions are carried out in aqueous
solution. There should be a separate waste
bottle for solid waste.
Knowing Nernst:
Non-equilibrium copper redox chemistry
Objectives:
(1) Calculate/measure stability of copper complexes
(2) Use ligands to change stabilities of metal species
HSAB concept: qualitative insights
Redox potentials/Nernst eqn: quantitative insights
Chemical species studies
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CuCl2
CuI
Cu(NH3)2+
Cu(en)22+
Cu(salen)n+
• Charge vs oxidation state
Oxidation states
• Sum of oxidation states = ionic charge on species
• Assumes unequal sharing of electrons
– more electronegative atom gets all of bond electrons
Oxidation states
• Sum of oxidation states = ionic charge on species
• Assumes unequal sharing of electrons
– more electronegative atom gets all of bond electrons
• Examples:
– MnO, Mn2O3, Mn3O4, MnO2, Mn5O8, KMnO4
• What differences are found between compounds
with difference oxidation numbers?
Atomic radius
Reactivity (redox potential)
Disproportionation
• 2 Fe4+
• 2 H2O2
→
→
Fe3+ + Fe5+
2 H2O + O2
• 2 Cu+
→
Cu0 + Cu2+
• Reverse of process: comproportionation
Sample redox potential calculation
CuCl2 + ammonia -> Cu(NH3)42+ + chloride
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
Cu2+ + Iˉ + eˉ
Cu2+ + Clˉ + eˉ
I2 + 2eˉ
Cu+ (aq) + eˉ
Cu2+(aq) + 2eˉ
CuCl + eˉ
Cu(NH3)42+ + 2eˉ
Cu2+(aq) + eˉ
CuI + eˉ
Cu(en)22+ + 2eˉ
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
CuI
CuCl
2Iˉ
Cu(s)
Cu(s)
Cu(s) + Clˉ
Cu(s) + 4NH3
Cu+ (aq)
Cu(s) + Iˉ
Cu + 2en
0.86V
0.54V
0.54V
0.52V
0.37V
0.14V
-0.12V
-0.15V
-0.19V
-0.50V
Reduction: Cu2+(aq) + 2eˉ
Oxidation: Cu(s) + 4NH3
Net:
Cu2+(aq) + 4NH3
 Cu(s)
 Cu(NH3)42+ + 2eˉ
 Cu(NH3)=2+
E0 = +0.37V
E0 = +0.12V
E0 = +0.49V
(5)
(7*)
Hard vs. soft
• Describes the general bonding trends of
chemical species (Lewis acids / Lewis bases)
• Hard acids prefer to bind to hard bases, while
soft acids prefer to bind to soft bases
most stable
complexes
Kstability = [AB] / [A][B]
least stable
complexes
harder
Monotonic variation in stability
Only two possible trends
softer
Hard: low polarizability,
primarily ionic bonding
Soft: high polarizability,
primarily covalent bonding
Lewis acids and bases
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Hard acids
H+, Li+, Na+, K+ , Rb+, Cs+
Be2+, Mg2+, Ca2+ , Sr2+, Ba2+
BF3, Al 3+, Si 4+, BCl3 , AlCl3
Ti4+, Cr3+, Cr2+, Mn2+
Sc3+, La3+, Ce4+, Gd3+, Lu3+,
Th4+, U4+, Ti4+, Zr4+, Hf4+,
VO4+, Cr6+,
Si4+, Sn4+
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Borderline acids
Fe2+, Co2+, Ni2+ , Cu2+,
Zn2+
Rh3+, Ir3+, Ru3+, Os2+
R3C+ , Sn2+, Pb2+
NO+, Sb3+, Bi3+
SO2
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Soft acids
Tl+, Cu+, Ag+, Au+, Cd2+
Hg2+, Pd2+, Pt2+, M0, RHg+,
Hg22+
BH3
CH2
HO+, RO+
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Hard bases
F-, ClH2O, OH-, O2CH3COO- , ROH, RO-, R2O
NO3-, ClO4CO32-, SO42- , PO43NH3, RNH2
N2H4
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Borderline bases
BrNO2-, N3SO32C6H5NH2, pyridine
N2
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Soft bases
H-, IH2S, HS-, S2- , RSH, RS-,
R2S
SCN- (bound through S), CN, RNC, CO
R3P, C2H4, C6H6
(RO)3P
Topics:
• Nernst equation (Electrochemistry problems)
G  nFE
RT
0
E 
ln K eq
nF
RT
0
EE 
ln Q
nF
Hard/soft references
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R.G. Pearson, Inorg. Chem., 27, p734 (1988).
R.G. Pearson, JACS, 85, p3533 (1963)
R.G. Pearson, J. Chem. Ed., 45, p581 AND p643 (1968)
R.G. Pearson, J. Chem. Ed. 64 (7): 561-567 JUL 1987 [471 cites]
• Hard and soft acids and bases, Ralph G. Pearson, editor. (1973)
480pp
• Hard and soft acids and bases {principle} in organic chemistry, T. L.
Ho (1977) 209pp