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UMass Amherst CHEM 242 - Non-equilibrium copper redox chemistry

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HandoutsKnowing Nernst: Non-equilibrium copper redox chemistrySafety / Waste disposalSlide 4Chemical species studiesOxidation statesSlide 7DisproportionationSample redox potential calculationSlide 10Hard vs. softSlide 12Slide 13Lewis acids and basesSlide 15Topics:Hard/soft referencesHandouts•Syllabus•Safety (detailed)•Web page is up and runningKnowing Nernst:Non-equilibrium copper redox chemistrySafety / 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 chemistryObjectives:(1) Calculate/measure stability of copper complexes(2) Use ligands to change stabilities of metal speciesHSAB concept: qualitative insightsRedox potentials/Nernst eqn: quantitative insightsChemical species studies•CuCl2•CuI•Cu(NH3)2+•Cu(en)22+•Cu(salen)n+•Charge vs oxidation stateOxidation states•Sum of oxidation states = ionic charge on species•Assumes unequal sharing of electrons–more electronegative atom gets all of bond electronsOxidation 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 radiusReactivity (redox potential)Disproportionation•2 Fe4+→ Fe3+ + Fe5+•2 H2O2 → 2 H2O + O2•2 Cu+ → Cu0 + Cu2+•Reverse of process: comproportionationSample redox potential calculationCuCl2 + ammonia -> Cu(NH3)42+ + chloride(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 -0.50VReduction: Cu2+(aq) + 2eˉ  Cu(s) E0 = +0.37V (5)Oxidation: Cu(s) + 4NH3  Cu(NH3)42+ + 2eˉ E0 = +0.12V (7*)Net: Cu2+(aq) + 4NH3 Cu(NH3)=2+ E0 = +0.49VHard 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 basesKstability = [AB] / [A][B]softerhardermost stable complexesleast stable complexesMonotonic variation in stabilityOnly two possible trendsHard: low polarizability, primarily ionic bondingSoft: high polarizability, primarily covalent bondingLewis 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+ •Hard bases F-, Cl- H2O, OH-, O2- CH3COO- , ROH, RO-, R2O NO3-, ClO4- CO32-, SO42- , PO43- NH3, RNH2 N2H4 •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)3PTopics:•Nernst equation (Electrochemistry problems)QnFRTEEKnFRTEnFEGeqlnln00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): 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)


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