Class Note for CHEM 112 at UMass(28)
Class Note for CHEM 112 at UMass(28)
Popular in Course
Popular in Department
This 10 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Massachusetts taught by a professor in Fall. Since its upload, it has received 16 views.
Reviews for Class Note for CHEM 112 at UMass(28)
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 02/06/15
Turn on Camtasia Recording In the reaction we just balanced which species is being reduced 2voz Zn 4H gt 2v02 2HZO an A v02 B Zn 0 v02 D Zn2 54E Question The following skeletal oxidationreduction reaction occurs under acidic conditions Write the balanced REDUCTION half reaction HNo3 Cr3 a NO CrO4239 1 Identify the species being reduced HNO3 or Cr Conclusion N is being Cr is being Balance each half reaction using the following steps a Balance all elements except oxygen or hydrogen b Balance oxygen by adding H20 c Balance hydrogen by adding H 1 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 Combine H OH into H20 Cancel out any waters that appear on both sides Skeleton Reaction HNO3 Cr3 9 NO CrO4239 Oxidation Reaction Cr3 9 CrO4239 amp 5 Combine Half Reactions HNO3 3H 3e39 9 NO 2H2O 7 CHECK Atom and charge must balance HNo3 Cr3 2H20 a NO CrO4239 5H Reactants H moles N mole O moles Cr mole Net Charge Products H moles N mole O moles Cr moe Net Charge The Masses amp Charges Balance Electrochemistry Alessandro Volta 1745 1827 Italian scientist and Inventor 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 disappears Electrons are transferred from Zn to Cu but there is no useful electric current Oxidation Reduction CHEMICAL CHANGE gt ELECTRIC CURRENT To obtain a useful current we separate the oxidizing and reducing agents so that electron transfer occurs thru an external wire 39Z39nzt ions This is accomplished in a GALVANIC or VOLTAIC cell A group of such cells is called a battery Electrochemical Cell oElectrons travel through ISalt bridge allows electrode compartments to move between a Terms Used for Voltaic Cells Direction uretemnn aw 4gt Elemude Lemme H 5m bridge Etedvulym Raduced nxidized a ramquot spades species mink y 39 iAniuns Dxidiled C h Reduned H spades a 5quot species 1 7 l ANUDE unrpartment CATHDDE Compartment OXIDATIUN UCUHS REDUCTION can 11 What occurs at the anode A Oxidation B Reduction C Electrons are produced D Electrons plate onto the anode E Electrons reaction with the anode to reduce the metal that is the anode iii 12 In a voltaic cell which direction do e flow A From the anode to the cathode B From the cathode to the anode C From the compartment where the oxidation occurs to the compartment where the reduction occurs D From the compartment where the oxidation occurs to the compartment where the reduction occurs E Through the salt bridge 13 The Cu l Cu2 and Ag l Ag Cell Vuttmeter Sait bridge contains Marioz 7 Cuanode if 5ND Net reattinn Eus 2 Amaq 4 Eu2aq 2 Ags 14 Table 201 sundanl Redmtion Potentials in Aqueous Snlution at 25 w Reduction HalfReadilyquot p w 729 2 6 a 2 F 2q 237 Hzozlaq 2 H aq 2 2 a 2 HZOU 177 PhDJs 5032an 4 mm 2 e a mom 2 mum 1585 worm a H laq g e a Mmaq 4 HZDU 151 mm 2 e a Nils 1u L1q2 e a 2 mm 135 C71072 laq14 H aq s e a 2 cmaq 7 H10 it 123 axle 4 H laq 4 e a 2 mm 1229 5724 2 e a 2 mm 103 Nag lzq 4 H laq 3 e a NDg 2 mm 095 atl laq HIM 2 e a Ll aq 2 BH aq 03 Hg aq 2 e a mo H355 13 Ag laq 2 a Aglx g u799 3 Mom 2 2 2 my 2 may E 2mm 2 a E aq 5 077 E 10 2 e a 2 man 7 a525 1 m7 2 mum 4 9 a 4 UH taq E u4n g uz laq 2 e 8 Ms E n237 g Sn aq 2 2 a 5mm a 015 E 2 H sql 2239 7 H147 H0i 5mm 2 2 a 5M5 5 n14 quot Ni aq 2 e a Nis quot 025 Vquotaq e a VZ aq n2ss Phsmls 2 2 a no sui taq 47355 Cdl taq 2 e a Mrs u4n FEZ uq 2 e a M n44 zni39laq 2 e a Zns n752 2 mam 2 2 a H2q 2 DH aq ua277 Al3 aq 2 r a Alls 155 Mgl39laq 2 e a 7495 237 Na laqy 22 Nasl 2714 K aq 22 Kls 2325 Li laq E a no 2345 um 39 15 ZnCu Electrochemical Cell wi re elect rons gt salt brid e Anode negative source of electrons Cathode positive sink for electrons 16 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 17 CELL POTENTIALS E Can t measure 12 reaction E directly Therefore measure it relative to a Standard Hydrogen Electrode SHE 2 Haq1 M 2e 3 H2g 1 atm E 18 Reduction of H by Zn Vultmetey Chemira y inert Pt eledmde 1 M 25 c 77 7 1 M 25 c 2 Haq 2 e Haw ZnsgtZn2zq 2 2 Net reac nn39 7nk 7 mm mm new 19