practice packet: oxidation reduction regents chemistry...
TRANSCRIPT
PracticePacket:OxidationReduction
Regents Chemistry: Mrs. Mintz
PracticePacketChapter14:OxidationReduction&Electrochemistry
1
Assigning Oxidation Numbers
Chemistry 200 Video Lesson 14.1
Objective:How do we assign atoms the correct oxidation number?
Oxidation & Reduction (Redox)Oxidation number• a number assigned to keep track of electron(s) gained
or lost in a redox rxns.
2. The Group 1 metals (Alkali Metals) in compoundsalways have an oxidation state of +1
3. The Group 2 metals (Alkali Earth Metals) incompounds always have an oxidation state of +2
4. The oxidation state for any simpleone-atom ion(monoatomic) is equalto its charge.
Rules for Assigning Oxidation Numbers (states)1. Free elements are assigned an oxidation state of zero
The hydrogen in H2, the sodium in Na, and the sulfur in S8 all have oxidation numbers of zero.
In MgCl2, the Mg2+ ion has an oxidation number of +2.Each of the Cl- ions has an oxidation number of -1.
In FeCl2, the Fe2+ ion has an oxidation number of +2, while in FeCl3 the Fe3+ ion has an oxidation number of +3.5. Fluorine in compounds is always assigned an
oxidation state of -1.
6. Hydrogen in compounds is always assignedan oxidation number of +1. (HCl).If combined w/ a metal, Hydrogenhas an oxidation # of -1. (LiH)
7. Oxygen in compounds is assigned an oxidation state of -2.
**When combined w/ Fluorine, Oxygen has an oxidation state of +2.**
8. The sum of the oxidation states of all the atoms in aspecies must be equal to the net charge on thespecies.
If the species is neutral, the sum of the oxidation states is zero.
If the species has a charge, the sum is equal to that charge.
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Determine the oxidation number of sulfur in H2SO4
H2SO4+1 -2+6
(-8)(+2) =0+6
Determine the oxidation number of nitrogen in NO3
-1
NO3-2+5
-1
(-6)= -1+5
Redox Reactions
Chemistry 200 Video Lesson 14.2
Objective:How do we identify substances being oxidized or reduced and the oxidizing and reducing agents.
How do we use this information to create half reactions ?
RedoxRedox reaction • a chemical rxn where electron(s) are transferred
from one atom to another
Oxidation• loss of electron(s) by an atom or ion & an increase
in oxidation # (Ca à Ca+2 )
Reduction• gain of electron(s) by an atom or ion & a
decrease in oxidation #( Mn+7 à Mn+2)
**Oxidation & Reduction occur simultaneously, they cannot occur separately**
+ 2e-
5e- +
Easy way to remember!!!
LEO says GERLEO = Loss of Electrons is OxidationGER = Gain of Electrons is Reduction
GER!!!!!Chemistry Yum Yum
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Oxidizing Agent
• the substance that causes the oxidation of othersubstances. They accept electron(s) easily &therefore are reduced
ex1: 5e- + Mn+7 à Mn+2
(gain of electrons, oxidation # reduced)
Reducing Agent
• the substance that allows another substance to bereduced. They lose electron(s) & therefore are oxidized
ex: Ca à Ca+2 + 2e- (loss of electrons, oxidation # increases)
**The species oxidized, the species reduced, the oxidizing agent or reducing agent must always be a reactant!!**
Gains Electrons
Oxidizing Agent
Reduced
Loses Electrons
Reducing Agent
Oxidized
Writing Half Reactions
• They show either the oxidation or reduction portion of aredox rxn, including electrons gained or lost
Half rxn for oxidation --> electrons are productsHalf rxn for reduction --> electrons are reactants
**Electronsgoonthesidew/themorepositiveoxid.#**
THERE’S AN EASIER WAY TO REMEMBER!!!
Creating Half Reactions from a Redox Reaction1. Assign oxidation numbers to determine the
substance oxidized & the substance reduced.
2. Write each half reaction, balance by atom, then byelectrons. The ONLY exception is a half rxn thecontains a diatomic element.
3. Identify the species oxidized, the species reducedthe oxidizing agent & the reducing agent.
KClO3 --> KCl + O2+1 -2+5
-6+1+5+1-1 0
Oxid: Red:
O-2 à O22 + 4e-
Cl+5 à Cl-16e- +
(reducing agent)
(oxidizing agent)
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Electrochemical Cells
Video Lesson 14.4
Objectives• Name the type of reactions involved in
electrochemical processes.• Describe how a voltaic cell produces
electrical energy.
Electrochemical Process• An electrochemical process is any
conversion between chemical and andelectrical energy (charged particles).
• All electrochemical processes involve redoxreactions.
• The two half reactions must be physicallyseparated to be used as a source ofelectrical energy.
Voltaic Cells• To obtain a useful current, we separate the oxidizing
and reducing agents so that electron transfer occurs thru an external wire.
• What is needed – Spontaneous Reaction o Salt Bridge
• connects the 2 containers & provides a passage for ions from one solution to another
o Electrodes• one of 2 surfaces that conduct electricity, the
site of oxidation & reduction rxns
Since Zn is higher on Table J, It will be Oxidized!
Anode Cathode
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Reduction occurs at the cathode
Oxidation occurs at the anode
From Anode to Cathode
Flow of Electrons Voltaic CellOverall Redox Rxn
Zn(s) + Cu+2(aq) --> Zn+2
(aq) + Cu(s)
Oxid:Red:
Zn(s) --> Zn+2(aq)+ 2e-
Cu+2(aq) --> Cu(s)2e- +
Species oxidized_____ Reducing agent______Species reduced_____ Oxidizing agent_____Anode_______ Cathode_______
Zn
Cu+2 Cu+2
Zn
Zn+2 Cu+2
Zn(s)anode -
Cu(s)cathode +
e- -->
Zn Cu
Zn Cu
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PracticePacket:Redox
Video14.1:OxidationNumbersDeterminetheoxidationnumberofEACHelementineachofthefollowingsubstances:
1. KMnO4
2. S8
3. Na2Cr2O7
4. CuCl2
5. H2SO4
6. PO4-3
7. zincoxide
8. water
9. calciumhydride
10. carbondioxide
Video14.2:RedoxReactionsWritingHalfReactions
Step1:BalancethehalfreactionbyatomusingcoefficientsStep2:Balancethehalfreactionbychargeusingelectrons(e-)
Electronsalwaysgoonthesidewiththemorepositiveoxidation#**Halfrxnsarewrittenonaperatombasis.Theonlyexceptionisifthehalfrxncontainsadiatomicelement**
MgàMg+2
O2àO-2
Cl+5àCl-1
Mn+2àMn+5
N-3àN2
S+6àS-2
3Cu+1à3Cu
6H+1à3H2
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Name: 14.1 Oxidation Numbers
1) –1 2) +2 3) –3 4) +4
1. What is the oxidation state of nitrogen inthe compound NH4Br?
1) –1 2) +2 3) +6 4) +4
2. What is the oxidation number of sulfur inNa2S2O3 ?
3. Given the balanced equation representinga reaction:
2KClO3(s) ® 2KCl(s) + 3O2(g)
1) –1 to +12) –1 to +5
3) + l to –14) +5 to –1
The oxidation state of chlorine in this reactionchanges from
1) +6 2) +2 3) +3 4) +8
4. What is the oxidation number of chromiumin the chromate ion, CrO42– ?
1) +7 2) +2 3) +3 4) +4
5. What is the oxidation number assigned tomanganese in KMnO4?
1) +1 2) +2 3) +3 4) +4
6. What is the oxidation state of nitrogen inNaNO2?
1) +12 2) +2 3) +3 4) +6
7. What is the oxidation number of chromiumin K2Cr2O7 ?
8. Given the reaction that occurs in anelectrochemical cell:
Zn(s) + CuSO4(aq) ® ZnSO4(aq) +Cu(s)
1) 0 to +22) 0 to –2
3) +2 to 04) –2 to 0
During this reaction, the oxidation number of Znchanges from
1) LiH2) H2O
3) H2S4) H2
9. In which substance does hydrogen havean oxidation number of zero?
1) CO2) CO2
3) CCl44) CH4
10. In which compound does carbon have anoxidation state of –4?
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PracticePacket:Redox
CreatingHalfReactionsfromRedoxReactionsStep1:AssignoxidationnumberstodeterminethesubstancesthathaveachangeinoxidationnumberStep2:Identifythetwohalfreactions&balanceeachhalfreactionStep3:Labeleachhalfreaction&identifythespeciesoxidized,thespeciesreduced,theoxidizingagent&thereducingagentNote:Thereactionprovidedtoyoumaybebalancedorunbalanced.Rememberthathalfreactionsaremadeonaperatombasis.TheONLYexceptionisahalfreactionthatcontainsadiatomicelement
Cu+2+MnàMn+4+CuSpeciesoxidized______________ OxidizingAgent______________
Speciesreduced______________ ReducingAgent______________
Oxidation: Reduction:
3Ag+1+FeàFe+3+3AgSpeciesoxidized______________ OxidizingAgent______________
Speciesreduced______________ ReducingAgent______________
Oxidation: Reduction:
Na+Cl2àNaClSpeciesoxidized______________ OxidizingAgent______________
Speciesreduced______________ ReducingAgent______________
Oxidation: Reduction:
2H2+O2à2H2O
Speciesoxidized______________ OxidizingAgent______________
Speciesreduced______________ ReducingAgent______________
Oxidation: Reduction:
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2S+3O2à2SO3Speciesoxidized______________ OxidizingAgent______________
Speciesreduced______________ ReducingAgent______________
Oxidation: Reduction:
2Fe+6HClà3H2+2FeCl3Speciesoxidized______________ OxidizingAgent______________
Speciesreduced______________ ReducingAgent______________
Oxidation: Reduction:
CH4+2O2àCO2+2H2OSpeciesoxidized______________ OxidizingAgent______________
Speciesreduced______________ ReducingAgent______________
Oxidation: Reduction:
2KClO3à2KCl+3O2
Speciesoxidized______________ OxidizingAgent______________
Speciesreduced______________ ReducingAgent______________
Oxidation: Reduction:
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Name: 14.2 Half Reactions
1) sharing of electrons2) sharing of protons3) transfer of electrons4) transfer of protons
1. An oxidation-reduction reaction involves the
1) transmutation2) reduction
3) oxidation4) neutralization
2. During which process does an atom gain one ormore electrons?
1) Mn4+ ® Mn3+ + e–
2) Mn4+ ® Mn7+ + 3e–
3) Mn4+ + e– ® Mn3+
4) Mn4+ + 3e– ® Mn7+
3. Which half-reaction correctly represents reduction?
1) less than the total number of electrons gained2) greater than the total number of electrons
gained3) equal to the total number of electrons gained4) equal to the total number of protons gained
4. In a redox reaction, the total number of electrons lostis
1) Zn2+ 2) Mg2+ 3) Co2+ 4) Ca2+
5. Which ion is most easily reduced?
1) Al Al3+ + 3e–
2) Al3+ + 3e– Al3) Cu Cu2+ + 2e–
4) Cu2+ + 2e– Cu
6. Given the balanced ionic equation representing areaction:
2Al(s) + 3Cu2+(aq) 2Al3+(aq) + 3Cu(s)Which half-reaction represents the reduction thatoccurs?
1)2)
3)4)
7. Which equation represents an oxidation-reductionreaction?
1) Cu + e– ® Cu+
2) Cu2+ + 2e– ® Cu3) Cu+ ® Cu + e–
4) Cu2+ ® Cu + 2e–
8. Which half-reaction shows conservation of charge?
1) Ba(NO3)2 + Na2SO4 ®BaSO4 + 2NaNO3
2) H3PO4 + 3KOH ®K3PO4 + 3H2O3) Fe(s) + S(s) ®FeS(s)4) NH3(g) + HCl(g) ®NH4Cl(s)
9. Which balanced equation represents anoxidation-reduction reaction?
1) Na+ + e– ® Na2) Na ® Na+ + e–
3) Cl2 + 2e– ® Cl–4) 2 Cl– ® Cl2 + 2e–
10. Which expression correctly represents a balancedreduction half-reaction?
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Lesson14.3:ActivitySeriesandSpontaneity
Table J:The table is arrangedwith themost reactivemetals at the topof thetableandtheleastreactivemetalsatthebottomofthetable.Whatthismeansisthatametal listedonthetablewillreactwiththecompoundofametal that isbelow it. For example, Zn is above Cu on the table. This means that Zn willreplaceCuinacompound.ZnwillbeoxidizedbyacompoundcontainingCu.TheCu+ionwillbereducedbyelementalZn0.MetalshigherontableJaremorelikelytobeoxidized.
Thereaction: Zn+Cu(NO3)2àCu+Zn(NO3)2willspontaneouslyoccur.
Foreachexamplebelow,ifareactionwilloccurspontaneouslybasedontheelementpositionsintheActivitySeries,completetheequationandbalanceit.Ifthereisnoreaction,writenoreaction.
1. Ag(s)+Cu(NO3)2(aq)à
2. Pb(s)+AuCl(aq)à
3. Au(s)+LiCl(aq)à
4. Mg(s)+Pb(NO3)2(aq)à
Determineifaspontaneousreactionwilloccur.Ifonewilloccur,writethebalancedoxidationandreductionhalfreactions.
1. Zn+Pb(NO3)2àPb+Zn(NO3)2
• Isthereactionspontaneous?________________
• Ifyes,writetheoxidation½reaction:
• Ifyes,writethereduction½reaction:
2. 3Zn+2Al(NO3)3à2Al+3Zn(NO3)2
• Isthereactionspontaneous?________________
• Ifyes,writetheoxidation½reaction:
• Ifyes,writethereduction½reaction:
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Video14.4:ElectrochemicalCellsAvoltaiccellisanelectrochemicalcell.(An
electrochemicalcellproduceselectriccurrentasaresultofaspontaneousredoxreaction,usedtomakebatteries.Theyconsistoftwohalf-cellsconnectedbyasaltbridgeandtwoelectrodesthatconnecttoaloadthatusestheelectricityproducedbythecell.)Anexampleanelectrochemicalcellisabattery.
OverallRedoxReaction:
Oxidation½Reaction: Reduction½Reaction:
SpeciesOxidized:_________________ Anode:______________
SpeciesReduced:_________________ Cathode:____________
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Anoperatingvoltaiccellhaszincandironelectrodes.Thecellandtheunbalancedionicequationrepresentingthereactionthatoccursinthecellareshownbelow.
1. Writethebalancedoxidationhalf-reactionforthiscell.
2. Writethebalancedreductionhalfreactionforthiscell.
3. If6molesofZnreact,howmanymolesofelectronswillbetransferred?
4. Explain,intermsofZnatomsandZnions,whythemassoftheZnelectrodedecreasesasthecelloperates.
5. Identifythesubatomicparticlesthatflowthroughthewireasthecelloperates.
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Astudentconstructsanelectrochemicalcellduringalaboratoryinvestigation.Whentheswitchisclosed,electronsflowthroughtheexternalcircuit.Thediagrambelowrepresentsthiscellandthereactionthatoccurs.
1. State,intermsofenergy,whythiscellisavoltaiccell.____________________________________________________________________________________________________________________________________________________________________________________________________________________________
2. DeterminethenumberofmolesofAlI(s)neededtocompletelyreactwith9.0molesofNi2+(aq)ions.
3. Writethebalancedhalf-reactionequationfortheoxidationthatoccurswhentheswitchisclosed.
4. Statethedirectionofelectronflowthroughthewireandwhentheswitchisclosed.______________________________________________________________________________________________________________
Lesson14.5:ElectrolyticCells.Electrolyticcellsuseelectricalenergytoforceanonspontaneouschemicalreactiontooccur.Reductionoccursatthecathode.Thecathodeistheelectrodewhereelectronsaresentandisthenegativeelectrode.Oxidationoccursattheanode.Theanodeistheelectrodewhereelectronsaredrawnawayfromandisthepositiveelectrode.
Electroplating MoltenSalt ElectrolysisofWater
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Electroplating:
CompletethechartElectrochemicalCells
VoltaicCell ElectrolyticCellExample: Example:ElectroplatingRedoxReactions
2electrodesAnode=oxidationNegative(-) Anode=Cathode= Cathode=ReductionNegative(-)Electronsflowfromanodetocathode
Useelectricalenergyforforceanonspontaneousredoxreactiontooccur(chemical)
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