Hard-Soft Acids and Bases: Altering the Cu + /Cu 2+ Equilibrium Objectives: (1) Calculate/predict...
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Transcript of Hard-Soft Acids and Bases: Altering the Cu + /Cu 2+ Equilibrium Objectives: (1) Calculate/predict...
Hard-Soft Acids and Bases: Altering the Cu+/Cu2+ Equilibrium
Objectives:
(1) Calculate/predict stability of copper oxidation states
(2) Use ligands to change stabilities of oxidation states
HSAB theory: qualitative predictions
Redox potentials: quantitative results
Oxidation States
• Sum of oxidation states = overall charge on species
• Assumes unequal sharing of electrons– more electronegative atom gets all electrons, preferred
oxidation state
• Examples: – MnO, MnO2, [K+ MnO4
-]
• What differences are found between metals in different oxidation states?
Atomic radius, reactivity
Hard/soft, redox potential
Hard vs. Soft Ligands and Metals
• Bonding trends of Lewis acids / Lewis bases
--electron acceptors / electron donors
•Polarizable (soft) vs non-polarizable (hard):
Thermodynamics of Hard/Soft Ligand/Metal Binding
--Hard-hard / soft-soft thermodynamically stronger binding / interaction
--Hard-soft / soft-hard thermodynamically weaker binding / interaction
HSAB theory:
Preferential selection of oxidation states by hard or soft ligand set
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+, Hg2
2+ BH3 CH2 HO+, RO+
• Hard bases F- H2O, OH-, O2- CH3COO- , ROH, RO-, R2O NO3-, ClO4- CO3
2-, SO42- , PO4
3- RNH2 N2H4
• Borderline bases
Cl- , Br- NH3, 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
G0 = -nFE0
n = mol e-
F = 96,500 Coulombs / mol e-
E0 = standard reduction potential in volts
G0 = free energy in joules
Electrochemical potentials E0
--Related to thermodynamic stability:
(1) Cu2+ + Iˉ + eˉ CuI 0.86V
(2) Cu2+ + Clˉ + eˉ CuCl 0.54V
(3) I2 + 2eˉ 2Iˉ 0.54V
(4) Cu+ (aq) + eˉ Cu(s) 0.52V
(5) Cu2+(aq) + 2eˉ Cu(s) 0.37V
(6) CuCl + eˉ Cu(s) + Clˉ 0.14V
(7) Cu(NH3)42+ + 2eˉ Cu(s) + 4NH3 -0.12V
(8) Cu2+(aq) + eˉ Cu+ (aq) -0.15V
(9) CuI + eˉ Cu(s) + Iˉ -0.19V
(10) Cu(en)22+ + 2eˉ Cu + 2en -0.50V
Electrochemical Potentials Used in Experiment 1:
E0
Redox Potential Calculation
Cu(aq)+2 + 4NH3 Cu(NH3)4+2
(5) Cu2+(aq) + 2eˉ Cu(s) 0.37V
(7) Cu(NH3)42+ + 2eˉ Cu(s) + 4NH3 -0.12V
Reduction: Cu2+(aq) + 2eˉ Cu(s) E0 = +0.37V
Oxidation: Cu(s) + 4NH3 Cu(NH3)42+ + 2eˉ E0 = +0.12V
Net: Cu2+(aq) + 4NH3 Cu(NH3)42+ E0 = +0.49V
(5) + (7*)
Disproportionation
• 2 Fe4+ → Fe3+ + Fe5+
• 2 H2O2 → 2 H2O + O2
--Two identical atoms in same oxidation state exchange one electron
--Take on two different oxidation states
2 Cu+ → Cu0 + Cu2+