Class Note for CHEM 112 at UMass(5)
Class Note for CHEM 112 at UMass(5)
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This 19 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 12 views.
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Date Created: 02/06/15
Turn on Camtasia Recording gm GredhL n4 OWL What kind of chemical reaction is found in batteries A Oxidation BAcidBase xidationReduction DThermodynamic E Kinetic m Balancing OxidationReduction Reactions 1 Assign oxidation numbers 2 Separate into oxidation and reduction half reactions 3 Balance each half reaction using the following steps 906 Balance all elements excep gen or hydrogen Balance oxygen by addin Balance hydrogen by addi Balance charge by adding e ectrons Electrons go on me muHT product side for UAILJAI ION reactions Electrons go on the LEFT reactant side for REDUCTION reactions In BASIC solution his additional step For every H ad 0 BOTH sides ofthe reaction Combine H OH into H20 Cancel out any waters that appear on both sides You should now have a balanced half reaction 3 4 Multiply balanced half reactions so an equal number of electrons are consumed aw produced 5 Add together half reactions 6 Clean up Combine identical substances and reduce coefficients to the lowest terms 7 CHECK Atom and charge must balance V0 Zn ha duction 0fVO2 with 21 The veganquot v39sye nw in acid Zn added with time the with time the ue v0 inn Firmly ween v ion is sumtv39un yeLan veg an is minced is fwthev veduced m gveen reduced Ln vv39uLEt v2 inn tu the v0 inn v inn Add Zn Balancing Equations Balance the following in acid solution v02 Zr gt v02 Zn2 EStjquot E tZJquot Step 1 Write the halfreactions Ox 2quot a 2 Red V024 Vow Step 2 Balance each halfreaction for mass OX 2 WI Red 2quot V02 gtVo 0 Add sz w vdeficient side and add H on other side for Hbalance Balancing Equations Step 3 Balance halfrea l ig for charge OX Zn 3 ZWquot739 Red m0 a vow H10 5quot 4 6quot Step 43 an appropriate factor gm W Ox 2m 4 2w 2 Wales Red 4H 2V02 azvo FZH o 2V0 gtZ 12vo242Ho Step252 J it d balancefnaITreact fens b WU39I ooneadxeide wlu 04 Ba Iancing Equations Never add 02 O atoms or 0239 to balance oxygen MA HzO Never add H2 or H atoms to balance hydrogen H Be sure to write the correct charges on all the ions Check your work at the end to make sure mass and charge are balanced PRACTICE In the reaction we just balanced which species is being reduced 2v02 Zn 4H gt 2vo2 2H20 Zn2 v02 W 7 V B Zn 0 v02 D Zn2 m 8 Questio he following skeletal oxidationreduction reaction occurs under onditions Write the balanced REDUCTION half rctioWNrb an oxidant 0 0 HNo3 Cr3 a NO Cro42 15c 422 gr 4 39739 1 Identify the species being reduced HNO3 or Cr3 3o HNOS 5 NO Conclusion N is being raiqu Cris being mutual Rahohm Bal ce each half reaction using the following steps a Balance all elements excer t ox fen or h droien fBalance oxygen by adding H20 c Balance hydrogen by adding H A Balance charge by adding electrons Electrons go on the RIGHT product side for OXIDATION reactions Electrons go on the LEFT reactant side for REDUCTION reactionslt IC solution do this ad 39 39 step For every OTH sides of the reaction Combine Ca out any waters that appear on both sides 5 a quot2 2H 0 3HquotHN03 I36 quot NO 2 10 Skeleton Reaction HNO3 Cr3 4 NO CrO4239 Oxidation 12Reaction Cri 9 CrO42 g 0X CV43934J4 H20 a Cv04391 Avg K K P 4 amp 5 Combine Half Reactions 6quot g c HNQ3 5H 59 9 NO 2H20 p t I o 5 5 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 12 Electrochemistry Alessandro Volta 1745 1827 Italian scientist and inventor Luigi Galvani 17371798 Italian scientist and inventor 13 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 Cu2 but there is no useful electric current Oxidation LvS gt Zia Ze Reduction cuff Zcr 7 CA 14 CHEMICAL CHANGE gt ELECTRIC CURRENT To obtain a useful current we separate the oxidizing and reducing agents so that electron Zn transfer occurs thru an external wire anquot i39Oth This is accomplished in a GALVANIC or VOLTAIC cell A group of such cells is called a battery 15 Electrochemical CG Zn gt Zn2 2e wire Cu2 2e gt Cu oxmlaiiov39 Oxidation L Reduction salt 39 39 Anode Zn bride Cathode Negative Positive Electrons travel through thale WW ISalt bridge allows mmmns Wm to move between electrode compartments LU Terms Used for Voltaic Cells 2v 00 gtzwn at Direction of electrun flaw 3 Elemde Electrode 3 3 A V t m Salt bridge Electrolyte inns in sututior V V ig eduEEId39 39 i 7 lt Anions Dxidized Reduced M species Eabum Species 77 7 MODE compartment CATHDDE compartment DEIDATIDN occurs UETION accurs 39 Q n 17 The Cu l Cu2 and Ag I Ag Cell u n ltmeter Salt b dge cuntain Mame x mf 39 O I 7 Net rea un Cuts E Agaq gt Ma aq 2 AME ifng D mi lP 18 What OCCUFS at the anode A Oxidation B Reduction C Electrons are produced D Electrons plate onto the anode E Electrons reaction e we V reduce the metal that is the anode 19
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