Class Note for CHEM 112 at UMass(19)
Class Note for CHEM 112 at UMass(19)
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Date Created: 02/06/15
Turn on Camtasia Recording 01494 20 204 Du Emily s Last SI session Monday 511 at 130 pm Library 1367 My review session Wednesday May 13th from 83010 am ISB 135 Prof Voigtman s review session Wednesday May 13th from 10 am noon ISB 135 In the reaction we just balanced which species is being reduced 2v02 Zn0 4Hgt 2vo2 2H20 an a Z 139 5 A V02 2 LEO B V5 3 K V02 quot1 ii 2 GE Z 2 n Oil Lie W Question The following skeleIaLDxidationreduction reaction occurs under acidic conditions Write the balanced REDUCTION half 5 reaction HNo3 Cr3 a NO CrO4239 1 Identify the species being reduced HNO3 or Cr u N o w m la n 3 Mn 0 NH 04 O ngz 03 Conclusion N is being lm N 5 7 Cris being Oxi ug 4 5 9 Balance each half reaction using the following steps Balance all elements except oxygen or hydrogen Balance oxygen by adding H20 Balance hydrogen by adding H Balance charge by adding electrons Electrons go on the RIGHT product side for OXIDATION reactions Electrons go on the LEFT reactant side for REDUCTION reactions e In BASIC solution do this additional step For every H add OH to BOTH sides of the reaction 0069 a gt Combine H OH into H20 390 45quot 4397 Cancel out any waters that appear on both sides bnlm 71am 54 440 4734 9 N 0 cut0 4 SHquot 95 2241 014 004458432510 1quot mo Alikle Q 5 gt 5H L30 r 00439 aa anceeacn hailrrac nn using lhelol uwmiskvs a Balance an elemenls axcamnxygsn 1 hydrogen b Balance exyuen w mm mo 2 Eaiance hydrogen Winding H a Ealance charge by iddmg eieclrons Eieclrons go rm me RIGHT Kimmie me rm oxmAnoN mwlmns Eisclmns go on me LEFT madam my car asoucnow reachons a MEASiCsomnon dumwsaddwunaislep Wm H m We am mm m mm H m m me u 6 1 1 23an um any ways max appear an bclh sidzs w w 1 I O m rm Hm 4 a N a L g f 5amp0 Cm ooq Eg y a L341 H mm mm Q a 5w 4 nm 004391 El I 139quot a 43 a 39 d1 WS no g wolf Skeleton Reaction HNO3 Cr 9 NO CrOf Oxidation 72 Reaction Cr 9 CrOf 4 amp 5 Combine Half Reactions HNO3 3H 3e 9 NO 2H2O 7 CHECK Atom and charge must balance HNo3 Cr3 2H20 a NO CrO4239 5H Reactants Products H moles H moles N mole N mole O moles O moles Cr mole Cr moe Net Charge Net Charge The Masses amp Charges Balance Electrochemistry Alessandro Volta 1745 1827 Italian scientist and Inventor Luigi Galvani 17371798 Italian scientist and inventor CHEMICAL CHANGE gt ELECTRIC CURRENT 2quot metal With time Cu plates out onto Zn metal strip and Zn strip Z disappears Electrons are transferred from Zn to Cu but there is no useful electric current 23 2p Zc39 03 971 39 C43 Oxidation Reduction 2n Ck 0 Zh39lr39l a a In 9 CHEMICAL CHANGE gt ELECTRIC CURRENT To obtain a useful current we a we a separate the oxidizing and elect rons g reducing agents so that electron salt transfer occurs thru an external wire IZn2 ioins This is accomplished in a GALVANIC or VOLTAIC cell A group of such cells is called a battery 10 Electrochemical Cell mar MD F gt 7 In quot msa 2u L eggs wa Electrons travel through u amp Sat bridge allows gampto move between electrode compartments Terms Used for Voltaic Cells niieetioii ureteeuen new aeuiede Etectrnie 7 Salt bridge Electinlyte Reduced Oxidized iensin species specie i q oxidized Hm Reduced H spades species i r 7 l ANUDE miiipsitment CATHDDE Compartment OXIDATIDN uctws REDUCTION can 12 rnUOw What occurs at the anode A Oxidation Reduction Electrons are produced Electrons plate onto the anode Electrons reaction with the anode to reduce the metal that is the anode 13 In a voltaic cell which direction do 6 A B flow From the anode to the cathode From the cathode to the anode From the compartment where the oxidation occurs to the compartment where the reduction occurs From the compartment where the oxidation occurs to the compartment where the reduction occurs Through the salt bridge 14 The Cu l Cu2 and Ag l Ag Cell Voltmeter Net reaction 015 2 Ag aq A Cu2aq 2 Ags 15 Table 201 Sundavd Redmion Pmnu39zk in Aqueous Salmon at 25 w E Reduniull HalfReam p v 3 729 2 e A 2 F aq 227 8 mum 2 H aq 2 2 A 2 mm 177 2 pnnzts Suf aq 1 mm 2 e A mm 2 H100 152 Mnartaq x H aq 5 2 A Mmaq 1 100 151 3 mm 2 e A Ants 150 mm 2 2 A 2 mm 125 g Cvzlhz uq 11 H aq s e A 2 cmaq 7 H1010 122 029 1 H taq 1 2 A 2 mm 122 aw 2 e A 2 Bv aq 122 Noam 1 man 3 2 A mm 2 H1011 295 acmq H20 2 e A man 2 DH aq 229 Hq aq 2 e A Hgm nass 13 AgWaql 2 A A98 E 279 5 Hgg zaq 2 2 A 2 mm g 27st 5 FE aq 2 A Fez taq g u771 E 125 2 2 A 2 ag 3 2535 f mm 2 H1DL 1 3 A 1 umaq E a1n Cu aq 2 e A Ms E nza7 Sn aq 2 2 A sni39zaq 215 m 2 7 A 7 ma Sn3 aq 2 2 A 577 1 211 umaq 2 2 A N715 5 722 V3 aq e A W iaq 7 was pnsmu 2 2 A mg sumac 72355 Cd aq 2 e A Eds run mm 2 e A 25 7211 9 Zn aq 2 2 A Zns 4753 2 gt11ou 2 e A 7429 2 0H aq 722277 Amaq 3 2 A mm 7155 Mgz aq 2 2 A Mg5 7237 Na aq 22 A Nas 72712 K aq 22 A 15 72925 Li aq 2 A 273 72015 a mug W w 91439 16 M 17 Zn FM 2quot Zn39 0619 Cufhvle Cu e c337V a 39 739 S l chM 39 39 Ow mhh llo och ZVH39QJquot lt3 2 04 Wags 2 cdk E CWM MV E mu 5 Eat Eu n 439 o39m LHoV V quu x Lloo bequot M 392 le quotb bequot 7 7393 k3ltM HI 5414031 Lp ou wuouof39lu Jg 18 ZnCu Electrochemical Cell wire Anode Cathode negative positive source of sink for electrons electrons 19 E0 for a Voltaic Cell From the table you see Fe is a better S B d agent than Cd 3 e Cd2 is a better agent than Fe2 Which reaction is at the cathode The anode Cd Fe 20 CELL POTENTIALS E Can t measure 12 reaction EO directly Therefore measure it relative to a Standard Hydrogen Electrode SHE 2 Haq 1 M 2e S H2g 1 atm E 21 Reduction of Ht by Zn athnde Chemiratty rm Pt electmde 10 M 25 5 ZnsgtZrnzaq 2 e 2 Haq z 3 Q Ham Net reac nn 7nk 7 mm mm new 22
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