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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 CuCl 2 CuI Cu(NH 3 ) 2+ Cu(en) 2 2+ 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, Mn 2 O 3, Mn 3 O 4, MnO 2, Mn 5 O 8, KMnO 4 What differences are found between compounds with difference oxidation numbers? Atomic radius Reactivity (redox potential)

Disproportionation 2 Fe 4+ →Fe 3+ + Fe 5+ 2 H 2 O 2 → 2 H 2 O + O 2 2 Cu + →Cu 0 + Cu 2+ Reverse of process: comproportionation

Sample redox potential calculation CuCl 2 + ammonia -> Cu(NH 3 ) chloride (1) Cu 2+ + Iˉ + eˉ  CuI0.86V (2)Cu 2+ + Clˉ + eˉ  CuCl0.54V (3)I 2 + 2eˉ  2Iˉ0.54V (4)Cu + (aq) + eˉ  Cu(s)0.52V (5)Cu 2+ (aq) + 2eˉ  Cu(s)0.37V (6)CuCl + eˉ  Cu(s) + Clˉ0.14V (7)Cu(NH 3 ) eˉ  Cu(s) + 4NH V (8) Cu 2+ (aq) + eˉ  Cu + (aq)-0.15V (9)CuI + eˉ  Cu(s) + Iˉ-0.19V (10)Cu(en) eˉ  Cu + 2en-0.50V

Reduction:Cu 2+ (aq) + 2eˉ  Cu(s)E0 = +0.37V(5) Oxidation:Cu(s) + 4NH 3  Cu(NH 3 ) eˉE0 = +0.12V(7*) Net:Cu 2+ (aq) + 4NH 3  Cu(NH 3 )= 2+ E0 = +0.49V

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

K stability = [AB] / [A][B] softerharder most stable complexes least stable complexes Monotonic variation in stability Only two possible trends

Hard: low polarizability, primarily ionic bonding Soft: high polarizability, primarily covalent bonding

Lewis acids and bases Hard acids H +, Li +, Na +, K +, Rb +, Cs + Be 2+, Mg 2+, Ca 2+, Sr 2+, Ba 2+ BF 3, Al 3+, Si 4+, BCl 3, AlCl 3 Ti 4+, Cr 3+, Cr 2+, Mn 2+ Sc 3+, La 3+, Ce 4+, Gd 3+, Lu 3+, Th 4+, U 4+, Ti 4+, Zr 4+, Hf 4+, VO 4+, Cr 6+, Si 4+, Sn 4+ Borderline acids Fe 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+ Rh 3+, Ir 3+, Ru 3+, Os 2+ R 3 C +, Sn 2+, Pb 2+ NO +, Sb 3+, Bi 3+ SO 2 Soft acids Tl +, Cu +, Ag +, Au +, Cd 2+ Hg 2+, Pd 2+, Pt 2+, M 0, RHg +, Hg 2 2+ BH 3 CH 2 HO +, RO + Hard bases F -, Cl - H 2 O, OH -, O 2- CH 3 COO -, ROH, RO -, R 2 O NO 3-, ClO 4- CO 3 2-, SO 4 2-, PO 4 3- NH 3, RNH 2 N 2 H 4 Borderline bases Br - NO 2-, N 3- SO 3 2- C 6 H 5 NH 2, pyridine N 2 Soft bases H -, I - H 2 S, HS -, S 2-, RSH, RS-, R 2 S SCN - (bound through S), CN -, RNC, CO R 3 P, C 2 H 4, C 6 H 6 (RO) 3 P

Topics: Nernst equation (Electrochemistry problems)

Hard/soft references 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): 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