Principles of Chemistry II © Vanden BoutTodayElectrochemistryelectrons moving aboutequilibrium with a control knob Principles of Chemistry II © Vanden BoutBatterieswhat is going on (the simple view)Cd on one sideNi3+ on the other side Principles of Chemistry II © Vanden BoutElectrons have a lower free energy in Ni2+ than Cd2+ (and Cd)Cd Ni3+2 e-Cd2+ 2Ni2+ Principles of Chemistry II © Vanden BoutTo make a battery you need theelectrons to flow "externally"Cd Ni3+Cd2+ 2Ni2+ 2e-Principles of Chemistry II © Vanden Boutwhat is really happening2NiO(OH) + Cd + H2O 2Ni(OH)2 + Cd(OH)2 How can we understand this?We need to know about Redox numbersThink in terms of half reactions Principles of Chemistry II © Vanden BoutFirst some language for the quizRedoxShort hand for chemistry that involvesOxidation and ReductionOxidation when an element loses electronsMn Mn2+ 2e-Reduction when an element gains electrons2H+ + 2e- H2 Principles of Chemistry II © Vanden BoutKeep it straightOIL RIGOxidation Is LossReduction Is GainLEO says GERLose Electrons OxidationGain Electrons ReductionJREMIT GROLJust REMember IT Gain Reduction Oxidation Loss Principles of Chemistry II © Vanden BoutOxidation numbersCHAPTER 4!!!Keeping track of chargeEasy in ions"Book keeping" in moleculesfor molecules oxidation numbers are a convention in which we imagine what the charge would be if it broke up into pieces(we can't really assign electrons to different elements)Principles of Chemistry II © Vanden BoutHow will we ever figure it out?There are rules.MgOIf we imagine this breaking up it would makeMg2+ and O2-So the "oxidation state" of Mg is 2+the "oxidation state" of O is 2- Principles of Chemistry II © Vanden Bout Principles of Chemistry II © Vanden BoutRule 6The sum of all oxidation numbers in a compound is equal to its chargeH2O 2 x oxidation number for H + oxidation number for O = 0 Principles of Chemistry II © Vanden BoutRule 1The oxidation state of an atom in an element is 0Example: O2(g), H2(g), C(s), Na(s), Hg(l)why?monatomic have no chargeIf diatomic break up they will end up as neutral atomsPrinciples of Chemistry II © Vanden BoutRule 2the oxidation state of a monatomic ion is the same as its chargeExample: Na+ is1+Fe3+ is 3+Fe2+ is 2+ Principles of Chemistry II © Vanden BoutRule 3In a compound with no metals H is assign to +1H2O H is 1+HCl H is 1+note: H2 is not a compound Principles of Chemistry II © Vanden BoutWhat is oxidation state of O in H2O?! A.! ! 0! B.! ! +1! C.! ! +2!! D.! ! -1! E.! ! -2Since H is +1, O must be -2 Principles of Chemistry II © Vanden BoutRule 4Oxygen is -2Rule 4bexcept in peroxides O2-compound with O-O bondsPrinciples of Chemistry II © Vanden BoutRule 5Most electronegative element isassigned its charge in an ionExample HClH is +1Cl is -1MgBr2Br is -1Mg is +2 Principles of Chemistry II © Vanden BoutWhat is oxidation state of Fe in Fe2O3?! A.! ! -3! B.! ! +1! C.! ! +2!! D.! ! +3! E.! ! -2Since O is -2, Fe must be +3 Principles of Chemistry II © Vanden BoutLet's look at a reactionWhat is happening to the oxidation number of iron in this reaction?In Fe2O3 it is +3in Fe it is 0Iron is being REDUCEDFe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g) Principles of Chemistry II © Vanden BoutLet's look at a reactionFe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g)What is happening to the oxidation number of carbon in this reaction?In CO it is +2in CO2 it is +4Carbon is being OxidizedPrinciples of Chemistry II © Vanden BoutLet's look at a reactionFe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g)CO is reducing the Fe2O3 to FeCO is the "reducing agent"it is doing the reducingFe2O3 is oxidizing the CO to CO2Fe2O3 is the "oxidizng agent"it is doing the oxidizing Principles of Chemistry II © Vanden BoutIn the following reaction what is the oxidizing agent?! A.! ! Fe! B.! ! O2! C.! ! Fe2O3!! D.! ! there is no oxidizing agent (oxidizer)4Fe(s) + 3O2(g) 2Fe2O3(s)Fe goes from 0 to +3 it is oxidized by the O2 Principles of Chemistry II © Vanden BoutWriting Half ReactionsH2O2 + I- I2 + H2OOne reaction for oxidation I goes from -1 to 0One reaction for reductionO goes from -1 to -2I- I2 H2O2 H2O Principles of Chemistry II © Vanden BoutBalancing Redox ReactionsPrinciples of Chemistry II © Vanden BoutOne reaction for oxidation I goes from -1 to 0One reaction for reductionO goes from -1 to -2I- I2 H2O2 H2O 2I- I2 2I- I2 +2e- Principles of Chemistry II © Vanden BoutBalancing Redox Reactions Principles of Chemistry II © Vanden BoutOne reaction for reductionO goes from -1 to -2H2O2 H2O H2O2 2H2O add H2O to balance O2H+ + H2O2 2H2O add H+ to balance H2e- + 2H+ + H2O2 2H2O add e- to balance charge Principles of Chemistry II © Vanden Bout2e-
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