Knowing Nernst: Nonequilibrium copper redox chemistry

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Knowing NernstNon-equilibrium copper redox
chemistry
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Knowing NernstNon-equilibrium copper redox
chemistry

• Objectives
• Calculate/measure stability of copper complexes
• Use ligands to change stabilities of metal species

HSAB concept qualitative insights Redox
potentials/Nernst eqn quantitative insights
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Chemical species studies

• CuCl2
• CuI
• Cu(NH3)42
• Cu(en)22
• Cu(salen)n
• Charge vs oxidation state

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Oxidation states

• Sum of oxidation states ionic charge on species
• Assumes unequal sharing of electrons
• more electronegative atom gets all of bond
  electrons

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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, MnO2, KMnO4

• What differences are found between compounds with
  difference oxidation numbers?

Atomic radius Reactivity (redox potential)
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Disproportionation

• 2 Fe4 ? Fe3 Fe5
• 2 H2O2 ? 2 H2O O2
• 2 Cu ? Cu0 Cu2
• Reverse of process comproportionation

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Sample redox potential calculation

• CuCl2 ammonia -gt Cu(NH3)42 chloride
• (1) Cu2 I e ? CuI 0.86V
• (2) Cu2 Cl e ? CuCl 0.54V
• (3) I2 2e ? 2I 0.54V
• (4) Cu (aq) e ? Cu(s) 0.52V
• (5) Cu2(aq) 2e ? Cu(s) 0.37V
• (6) CuCl e ? Cu(s) Cl 0.14V
• (7) Cu(NH3)42 2e ? Cu(s) 4NH3 -0.12V
• (8) Cu2(aq) e ? Cu (aq) -0.15V
• (9) CuI e ? Cu(s) I -0.19V
• (10) Cu(en)22 2e ? Cu 2en -0.50V

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• Reduction Cu2(aq) 2e ? Cu(s) E0
  0.37V (5)
• Oxidation Cu(s) 4NH3 ? Cu(NH3)42
  2e E0 0.12V (7)
• Net Cu2(aq) 4NH3 ? Cu(NH3)42 E0
  0.49V

• DG0 -nFE0
• n mol e-
• F 96,500 C / mol e-
• E0 standard reduction potential in V (1M conc,
  1 atm pressure)
• 1 Joule (1 Volt)(1 Coulomb)

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Nernst Equation
at 298 K
n number of mol e- R 8.3145 J/K-mol F
96,500 C / mol e- E0 standard reduction
potential in V (1M conc, 1 atm pressure)
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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

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most stable complexes
Kstability AB / AB
least stable complexes
softer
harder
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Hard low polarizability, primarily ionic bonding
Soft high polarizability, primarily covalent
bonding
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Lewis acids and bases

• 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

• Borderline acids
• Fe2, Co2, Ni2 , Cu2, Zn2 Rh3, Ir3, Ru3,
  Os2 R3C , Sn2, Pb2 NO, Sb3, Bi3 SO2

• Soft acids
• Tl, Cu, Ag, Au, Cd2 Hg2, Pd2, Pt2, M0,
  RHg, Hg22 BH3 CH2 HO, RO

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• Borderline bases
• Br- NO2-, N3- SO32- C6H5NH2, pyridine N2  

• Soft bases
• H-, I- H2S, HS-, S2- , RSH, RS-, R2S SCN-
  (bound through S), CN-, RNC, CO R3P, C2H4, C6H6
  (RO)3P 

• Hard bases
• F-, Cl- H2O, OH-, O2- CH3COO- , ROH, RO-, R2O
  NO3-, ClO4- CO32-, SO42- , PO43- NH3, RNH2
  N2H4

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Experimental Details
--Part G watch out for oil drips and ethanol
flames
--do not throw away stir bars--recover them
--dissolve all of the H2salen and Cusalen--no
precipitates