Oxidation and Reduction Reactions
description
Transcript of Oxidation and Reduction Reactions
Oxidation and Reduction Oxidation and Reduction ReactionsReactions
Oxidation (Read only)Oxidation (Read only)
Original definition:Original definition:When substances combined with oxygen.When substances combined with oxygen.
Ex:Ex:All combustion (burning) reactionsAll combustion (burning) reactionsCHCH44(g) + 2O(g) + 2O22(g) (g) COCO22(g) + 2H(g) + 2H22O(l)O(l)
All “rusting” reactionsAll “rusting” reactions4Fe(s) + 3O4Fe(s) + 3O22(g)(g) 2Fe2Fe22OO33(s)(s)
Reduction (Read Only)Reduction (Read Only)
Original Definition:Original Definition:Reaction where a substance “gave up” oxygen.Reaction where a substance “gave up” oxygen.
Called “reductions” because they producedCalled “reductions” because they producedproducts that were “reduced” in mass becauseproducts that were “reduced” in mass becausegas escaped.gas escaped.
Ex:Ex:2Fe2Fe22OO33(l) + 3C(s)(l) + 3C(s) 4Fe(l) + 3CO 4Fe(l) + 3CO22(g)(g)
Deals with movement of Deals with movement of ELECTRONSELECTRONSduring a chemical reaction.during a chemical reaction.(Oxygen doesn’t have to be present)(Oxygen doesn’t have to be present)
Oxidation/ReductionOxidation/Reduction
Electron Transfer ReactionsElectron Transfer Reactions
Oxidation:Oxidation: LOSS of one or more electrons. LOSS of one or more electrons.
Reduction:Reduction: GAIN of one or more electrons GAIN of one or more electrons
Electron Transfer ReactionsElectron Transfer Reactions
Oxidation & reduction always occur together.Oxidation & reduction always occur together.Electrons travel from what is oxidized towardsElectrons travel from what is oxidized towardswhat is reduced. what is reduced. One atom loses e-, the other gains e-One atom loses e-, the other gains e-
Redox ReactionsRedox Reactions::
ALWAYSALWAYS involve changes in charge involve changes in charge A competition for electrons between atoms!A competition for electrons between atoms!
Remember!!Remember!!
Or…RememberOr…Remember
Conservation of “Charge”Conservation of “Charge”
Total electrons lost = Total electrons gainedTotal electrons lost = Total electrons gained
Oxidizing/Reducing AgentsOxidizing/Reducing Agents
Oxidizing AgentOxidizing Agent::substance reducedsubstance reduced Gains electronsGains electrons
Reducing Agent:Reducing Agent: substance oxidizedsubstance oxidized Loses electronsLoses electrons
The “Agent” is the “opposite”The “Agent” is the “opposite”
Assigning Oxidation NumbersAssigning Oxidation Numbers
Practice ProblemsPractice Problemshttp://www.usca.edu/chemistry/genchem/oxhttp://www.usca.edu/chemistry/genchem/oxnumb.htmnumb.htm
Animation of Oxidation and ReductionAnimation of Oxidation and Reductionhttp://www.ausetute.com.au/redox.htmlhttp://www.ausetute.com.au/redox.html
Identify What is Changing in Identify What is Changing in ChargeCharge
What is oxidized and reduced?What is oxidized and reduced?What are the oxidizing and reducing agents?What are the oxidizing and reducing agents?
Ex:Ex:
3Br3Br22 + 2AlI + 2AlI33 2AlBr2AlBr33 + 3I + 3I22
00 +3 -1 +3 -1 +3 -1 0 +3 -1 0
3Br3Br22 + 2AlI + 2AlI33 2AlBr2AlBr33 + 3I + 3I22
BrBr22 is reduced and is the oxidizing agent is reduced and is the oxidizing agent
II-1-1 is oxidized and is the reducing agent is oxidized and is the reducing agent
What is oxidized and reduced?What is oxidized and reduced?What are the oxidizing and reducing agents?What are the oxidizing and reducing agents?
Mg + CuSOMg + CuSO44 MgSOMgSO44 + Cu + Cu
2K + Br2K + Br22 2KBr2KBr
Cu + 2AgNOCu + 2AgNO33 Cu(NO Cu(NO33))22 + 2Ag + 2Ag
NOTE: NOTE: Atoms in a polyatomic ion DO NOT change in charge!Atoms in a polyatomic ion DO NOT change in charge!
0 +2 +2 00 +2 +2 0
Mg + CuSOMg + CuSO44 MgSOMgSO44 + Cu + CuMg oxidized (reducing agent)Mg oxidized (reducing agent)CuCu+2+2 reduced (oxidizing agent) reduced (oxidizing agent)
0 0 +1 -10 0 +1 -1
2K + Br2K + Br22 2KBr2KBrK oxidized (reducing agent)K oxidized (reducing agent)BrBr2 2 reduced (oxidizing agent)reduced (oxidizing agent)
00 +1 +1 +2 0+2 0
Cu + 2AgNOCu + 2AgNO33 Cu(NO Cu(NO33))22 + 2Ag + 2AgCu oxidized (reducing agent)Cu oxidized (reducing agent)AgAg+1+1 reduced (oxidizing agent) reduced (oxidizing agent)
Redox or Not Redox Redox or Not Redox (that is the question…)(that is the question…)
Redox Reactions:Redox Reactions: must have atoms changing in must have atoms changing incharge.charge.
Not all reactions are redox.Not all reactions are redox.
Easy way to spot a redox reaction!!!Easy way to spot a redox reaction!!!Look for elements entering and leavingLook for elements entering and leavingcompoundscompounds..
Is it Redox?Is it Redox?Look for Changes in Charge! Look for Changes in Charge! Are elements entering and leaving compounds?Are elements entering and leaving compounds?
Synthesis:Synthesis:
Ex:Ex: 2H2H22 + O + O22 2H2H22OO
Decomposition:Decomposition:
Ex:Ex: 2KClO2KClO33 2KCl + 3O2KCl + 3O22
Is it Redox?Is it Redox?
SynthesisSynthesis: : YESYES00 0 0 +1 -2 +1 -2
Ex:Ex: 2H2H22 + O + O22 2H2H22OO
DecompositionDecomposition: : YESYES +1 +5 -2+1 +5 -2 +1 -1 0 +1 -1 0
Ex:Ex: 2KClO2KClO33 2KCl + 3O2KCl + 3O22
Is it Redox?Is it Redox?
Combustion:Combustion:
CHCH44 + 2O + 2O22 COCO22 + 2H + 2H2200
Single Replacement:Single Replacement:
Zn + CuClZn + CuCl22 ZnClZnCl22 + Cu + Cu
Is it Redox?Is it Redox?
Combustion:Combustion: YESYES-4 +1 0 +4 -2 +1 -2-4 +1 0 +4 -2 +1 -2
CHCH44 + 2O + 2O22 COCO22 + 2H + 2H2200
Single Replacement:Single Replacement:YESYES 0 +2 -1 +2 -1 00 +2 -1 +2 -1 0
Zn + CuClZn + CuCl22 ZnClZnCl22 + Cu + Cu
Is it Redox?Is it Redox?
Double Replacement:Double Replacement:
AgNOAgNO33 + LiCl + LiCl AgCl + LiNO AgCl + LiNO33
Is it Redox?Is it Redox?
Double Replacement:Double Replacement: NO!!!!NO!!!!
Ions switch partners, but don’t change in chargeIons switch partners, but don’t change in charge
+1 +5 -2 +1 -1 +1 -1 +1 +5 -2+1 +5 -2 +1 -1 +1 -1 +1 +5 -2
AgNOAgNO33 + LiCl + LiCl AgCl + LiNO AgCl + LiNO33
Remember charges of atoms inside polyatomic ionsRemember charges of atoms inside polyatomic ionsdo not change!do not change!
Writing Half ReactionsWriting Half Reactions
Redox Reactions are composed of two partsRedox Reactions are composed of two partsor half reactions.or half reactions.
Half Reactions Show:Half Reactions Show:Element being oxidized or reduced.Element being oxidized or reduced.Change in chargeChange in charge# of electrons being lost or gained# of electrons being lost or gained
Writing Half ReactionsWriting Half Reactions0 00 0 +1 -1 +1 -1
2Na + F2Na + F22 2NaF2NaF
Oxidation:Oxidation: NaNa Na Na+1+1 + 1e- + 1e-oror 2Na2Na 2Na 2Na+1 +1 + 2e- + 2e-
Note: e- are “lost” (on the right of arrow)Note: e- are “lost” (on the right of arrow)
Reduction:Reduction: F + 1e-F + 1e- F F-1-1
oror FF22 + 2e- + 2e- 2F 2F-1-1
Note: e- are “gained” (on the left of arrow)Note: e- are “gained” (on the left of arrow)
Ox’s Have Tails!!Ox’s Have Tails!!Oxidation Half reactions always have Oxidation Half reactions always have
“tails” of electrons“tails” of electrons
NaNa Na Na+1+1 + 1e- + 1e-
00 +2 -1 +2 -1 +2 -1 0+2 -1 0
Zn + CuClZn + CuCl22 ZnClZnCl22 + Cu + Cu
Ox:Ox: ZnZn ZnZn+2+2 + 2e- + 2e-
Red:Red: CuCu+2+2 + 2e- + 2e- CuCu
Balancing Simple Redox RxnsBalancing Simple Redox Rxns
Must be:Must be:
Balanced for MassBalanced for Mass ATOMS balanceATOMS balance
Balanced for ChargeBalanced for Charge Total e- Lost = Total e- GainedTotal e- Lost = Total e- Gained
Balancing Harder Balancing Harder Redox ReactionsRedox Reactions
(Honors)(Honors)
Oxidation Number MethodOxidation Number Method(Balancing in Acid Solution)(Balancing in Acid Solution)
• Find ox #’s and use brackets to connect elementsFind ox #’s and use brackets to connect elementschanging in charge.changing in charge.
• Balance atoms changing in chargeBalance atoms changing in charge• Find total e- involved in each changeFind total e- involved in each change• If necessary balance e- by multiplicationIf necessary balance e- by multiplication• Balance all other atoms except H and OBalance all other atoms except H and O• Balance oxygen by adding HBalance oxygen by adding H22O to side deficientO to side deficient• Balance hydrogen by adding HBalance hydrogen by adding H+1+1 to side deficient to side deficient• Check for balance with respect to atoms and charge.Check for balance with respect to atoms and charge.
Half Reaction Method Half Reaction Method (Ion/Electron Method)(Ion/Electron Method)
(In acid solution)(In acid solution)
Separate equation into two “basic” half reactionsSeparate equation into two “basic” half reactions Balance all atoms except H and OBalance all atoms except H and O Balance oxygen by adding HBalance oxygen by adding H22OO Balance hydrogen by adding HBalance hydrogen by adding H+1+1
Balance charge by adding electrons to more Balance charge by adding electrons to more positive sidepositive side
If necessary balance e- by multiplicationIf necessary balance e- by multiplication Add together half reactions and simplifyAdd together half reactions and simplify Check for balance of atoms and chargeCheck for balance of atoms and charge
Applications of Redox ReactionsApplications of Redox Reactions
Corrosion of MetalsCorrosion of Metalsthe metal gets oxidizedthe metal gets oxidizedforming metal oxides on forming metal oxides on the surfacethe surface
Prevention:Prevention: Use paint, oil, Use paint, oil,plating or attach to negativeplating or attach to negativeterminal of a battery.terminal of a battery.
Gold doesn’t rust…Why?
Photograph DevelopmentPhotograph Development involves oxidation and involves oxidation andreduction of silver atoms and ionsreduction of silver atoms and ions
BleachBleach acts on acts onstains by oxidizingstains by oxidizingthem, getting reduced them, getting reduced in the processin the process
ExplosivesExplosives form formneutral gases like Nneutral gases like N22
from compounds!from compounds!
Reactivity of MetalsReactivity of Metals
Reference Table JReference Table J
Metals Higher on Table J Metals Higher on Table J are more ‘active” are more ‘active”
It is easier for more “active” It is easier for more “active” metals to be oxidized metals to be oxidized or lose electrons.or lose electrons.
Copper replaces silver!
Cu0(s) + AgNO3(aq) Ag0(s) + CuNO3(aq)
Ag0(s) + CuNO3(aq) wouldn’t happen!!!
Reactivity of NonmetalsReactivity of Nonmetals
Reference Table JReference Table J
Nonmetals higher on Table J Nonmetals higher on Table J are more “active” are more “active”
It is easier for more “active” It is easier for more “active” nonmetals to “gain” electrons nonmetals to “gain” electrons and be reduced.and be reduced.
Electrochemical Cells (Batteries)Electrochemical Cells (Batteries)
Chemical reaction that produces electricity.Chemical reaction that produces electricity.Called “voltaic cells” as they produce voltageCalled “voltaic cells” as they produce voltage
This happens SPONTANEOUSLY.This happens SPONTANEOUSLY.
Moving Electrons = ElectricityMoving Electrons = Electricity
Electrons given off by oxidized substanceElectrons given off by oxidized substancetravel towards substance being reduced.travel towards substance being reduced.
Traveling electrons moveTraveling electrons movethrough “external circuit”through “external circuit”where they do work.where they do work.
How do the Electrons Move?How do the Electrons Move?
Batteries often contain 2 metals.Batteries often contain 2 metals.
Start with Table JStart with Table JElectrons travel from the more “Active metal”Electrons travel from the more “Active metal”toward the less active metal.toward the less active metal.
Metal above = oxidizedMetal above = oxidizedIon on Metal below = reducedIon on Metal below = reduced
Electrons flow Electrons flow ““Down Table JDown Table J””
From metalFrom metalabove to ion ofabove to ion ofmetal belowmetal below
e-
Parts of a Simple Battery Parts of a Simple Battery (Voltaic Cell)(Voltaic Cell)
Made of Two “Half Cells” containing:Made of Two “Half Cells” containing:
2 Metal Electrodes2 Metal Electrodes 2 Solutions of Ions2 Solutions of IonsExternal WireExternal WireSalt BridgeSalt Bridge
Electrons need to flow in a “circuit” thatElectrons need to flow in a “circuit” thatis connected.is connected.
External WireExternal Wire: : allows electrons to flowallows electrons to flowbetween metal electrodesbetween metal electrodes
Salt Bridge:Salt Bridge: allows ions allows ions to flow between solutionsto flow between solutions
Zn/ZnZn/Zn+2+2//Cu//Cu+2+2/Cu/Cu
What is Ox/Red?What is Ox/Red?
See Table JSee Table J
Metal above is oxidizedMetal above is oxidizedZnZnIon of metal below reducedIon of metal below reducedCuCu+2+2
Which way do electronsWhich way do electronsflow in the external wire?flow in the external wire?
See Table JSee Table J
Electrons flow “Down” theElectrons flow “Down” thetable from what is oxidizedtable from what is oxidizedtowards what is reduced.towards what is reduced.
from Zn to Cufrom Zn to Cu
e-
Which electrode is negative?Which electrode is negative?Which electrode is positive?Which electrode is positive?
Electrons flow from negative toElectrons flow from negative topositive electrode.positive electrode.
Negative electrode: ZnNegative electrode: ZnPositive electrode: CuPositive electrode: Cu
e-
Which electrode is theWhich electrode is theanode and cathode?anode and cathode?
AnodeAnode: metal electrode : metal electrode where oxidation occurswhere oxidation occurs
ZnZn
CathodeCathode: metal electrode : metal electrode where reduction occurswhere reduction occurs
CuCu
RememberRememberAN OXAN OX
RED CATRED CATAnode is where oxidation happensAnode is where oxidation happens
Cathode is where reduction happensCathode is where reduction happens
What are the Half Reactions?What are the Half Reactions?What is the Net Equation?What is the Net Equation?
Ox: Ox: ZnZn00 ZnZn+2+2 + 2e- + 2e-
Red:Red:CuCu+2+2 + 2e- + 2e- Cu Cu00
Net: (add ½ reactions)Net: (add ½ reactions)ZnZn00 + Cu + Cu+2+2 ZnZn+2 +2 + Cu+ Cu00
Make sure final net equation is Make sure final net equation is balanced for electrons and atoms!balanced for electrons and atoms!
e-
Which electrode gains/loses weight?Which electrode gains/loses weight?
Look at half reactions!!Look at half reactions!!Which one forms solid metal?Which one forms solid metal?Which one forms dissolved ions?Which one forms dissolved ions?
Ox: Ox: ZnZn00 ZnZn+2+2 + 2e- + 2e-Red:Red:CuCu+2+2 + 2e- + 2e- Cu Cu00
Zinc electrode loses massZinc electrode loses massCopper electrode gains massCopper electrode gains mass
Which way to do the ions in the salt Which way to do the ions in the salt bridge “migrate” or move?bridge “migrate” or move?
Remember:Remember:““The negative ions complete the circuit”The negative ions complete the circuit”
(The ions actually end up moving towards(The ions actually end up moving towardsthe solution of opposite charge that forms.)the solution of opposite charge that forms.)
Follow the ionsFollow the ions
http://www.mhhe.com/physsci/chemistry/ehttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swfssentialchemistry/flash/galvan5.swf
Dead BatteryDead Battery
Voltage = 0Voltage = 0
Means the reaction in the battery hasMeans the reaction in the battery hasreached reached EQUILIBRIUM.EQUILIBRIUM.
You try it…You try it…Mg/MgMg/Mg+2+2//Al//Al+3+3/Al/Al
• Draw and label BatteryDraw and label Battery• What is oxidized/reduced?What is oxidized/reduced?• What are the half reactions and net(balanced)?What are the half reactions and net(balanced)?• What is the neg/pos electrode?What is the neg/pos electrode?• What is the anode/cathode?What is the anode/cathode?• Which way do e- flow in wire?Which way do e- flow in wire?• Which way do -/+ ions flow in salt bridge?Which way do -/+ ions flow in salt bridge?• Which electrode gains/loses mass?Which electrode gains/loses mass?
Finding Voltage of a Battery Finding Voltage of a Battery (Honors)(Honors)
Use Voltage TableUse Voltage TableFind your half reactions and record voltageFind your half reactions and record voltage
Note:Note:All ½ reactions shown are reductions.All ½ reactions shown are reductions.For oxidation, reverse the sign of the voltageFor oxidation, reverse the sign of the voltage
Nerntz Equation (Honors)Nerntz Equation (Honors)
Find voltage of a battery when the conc. of dissolvedFind voltage of a battery when the conc. of dissolvedions is not 1 Molar (as on “standard voltage” table)ions is not 1 Molar (as on “standard voltage” table)
EEcellcell = E = E00 – – 0.0592 0.0592 log log [product ion][product ion]xx
nn [reactant ion] [reactant ion]yy
n = total # of moles electrons being transferredn = total # of moles electrons being transferred
The concentration of dissolved ions can affect voltage. The concentration of dissolved ions can affect voltage. Greater concentration of reactant ions (see net)Greater concentration of reactant ions (see net)
increases the overall voltage.increases the overall voltage.
Electrolytic Cells & Electrolytic Cells & Electrolysis ReactionsElectrolysis Reactions
Uses electricity to “split” or “lyse” aUses electricity to “split” or “lyse” acompound into it’s neutral elementscompound into it’s neutral elements
An outside electrical source provides electronsAn outside electrical source provides electronsto force a to force a non-spontaneous redox reactionnon-spontaneous redox reaction to tooccur.occur.
Electrolysis Set UpElectrolysis Set Up
Single Cell filled with electrolyte with +/- ionsSingle Cell filled with electrolyte with +/- ions
Attach battery to two electrodes.Attach battery to two electrodes.
Electrodes are made of an inert substance Electrodes are made of an inert substance (like platinum or graphite) that conducts. (like platinum or graphite) that conducts.
Electrodes don’t chemically change like in a battery, Electrodes don’t chemically change like in a battery, they just provide currentthey just provide current
Pulls electrons off one electrodePulls electrons off one electrodeMaking it POSITIVEMaking it POSITIVE
Adds electrons onto one electrodeAdds electrons onto one electrodeMaking it NEGATIVEMaking it NEGATIVE
Role of the BatteryRole of the Battery
Which Way do the Ions Move?Which Way do the Ions Move?
To electrode ofTo electrode ofopposite chargeopposite charge
At neg. electrodeAt neg. electrodeelectrons are gainedelectrons are gained by ion by ion(reduction at CATHODE)(reduction at CATHODE)
At positive electrodeAt positive electrodeelectrons are lostelectrons are lost by ion by ion(oxidation at ANODE)(oxidation at ANODE)
What is Oxidized/Reduced?What is Oxidized/Reduced?
RememberRememberAN OXAN OX
RED CATRED CATAnode is where oxidation happensAnode is where oxidation happens
Cathode is where reduction happensCathode is where reduction happens
Half Reactions & Net EquationHalf Reactions & Net EquationRxn at Anode:Rxn at Anode: (Ox) (Ox)ClCl-- Cl + 1e- Cl + 1e-Or more correctlyOr more correctly DIATOMIC!!!!!!DIATOMIC!!!!!!2Cl2Cl-- Cl Cl22 + 2e- + 2e-
Rxn at Cathode:Rxn at Cathode: (Red) (Red)NaNa+ + + 1e-+ 1e- Na Na(Multiply by 2 to balance electrons)(Multiply by 2 to balance electrons)
NET:NET: 2Na2Na++ + 2Cl + 2Cl-- 2Na + Cl 2Na + Cl22
Determining Voltage NeededDetermining Voltage Needed
Use the Voltage Table to determine the totalUse the Voltage Table to determine the totalvoltage needed to run the Electrolytic cell.voltage needed to run the Electrolytic cell.
Total voltage should be a NEGATIVE numberTotal voltage should be a NEGATIVE number
Electrolysis of Molten NaCl (l)Electrolysis of Molten NaCl (l)
Electrolysis of PbClElectrolysis of PbCl22(l)(l)
What is oxidized?What is oxidized?
What is reduced?What is reduced?
What are the ox/redWhat are the ox/redhalf reactions?half reactions?
What is the netWhat is the netequation?equation?Negative
ElectrodePositive Electrode
Electrolysis of PbClElectrolysis of PbCl22(l)(l)
Oxidized: ClOxidized: Cl-- Reduced: PbReduced: Pb+2+2
Half ReactionsHalf ReactionsOx:Ox: ClCl-1-1 Cl + 1e-Cl + 1e-
2Cl2Cl-1-1 ClCl22 + 2e- + 2e-
Red:Red: PbPb+2+2 + 2e- + 2e- PbPb
Net:Net: PbPb+2+2 + 2Cl + 2Cl-1-1 Pb + ClPb + Cl22
Electrolysis of NaCl(aq)Electrolysis of NaCl(aq)
Electrolysis of NaCl (aq)Electrolysis of NaCl (aq)
Electrolysis of WaterElectrolysis of Water
At Positive Electrode:At Positive Electrode:Ox: Ox: OO-2-2 O + 2e- O + 2e-
but there is a diatomic!but there is a diatomic!2O2O-2-2 OO22 + 4e- + 4e-
At Negative ElectrodeAt Negative ElectrodeRed:Red: HH+1+1 + 1e- + 1e- HH
but there is a diatomic!but there is a diatomic!2H2H+1+1 + 2e- + 2e- HH22
Net:Net: 2H2H22O O 2H2H22 + O + O22
Lemon Battery DemoLemon Battery Demo http://youtu.be/AY9qcDCFeVIhttp://youtu.be/AY9qcDCFeVI
Electrolysis of Copper SulfateElectrolysis of Copper Sulfate http://youtu.be/xBz9HJ32Ouwhttp://youtu.be/xBz9HJ32Ouw
Electrolysis of Water/ Silver Nitrate and Cu reactionElectrolysis of Water/ Silver Nitrate and Cu reaction http://youtu.be/Bcfp8VtcrSAhttp://youtu.be/Bcfp8VtcrSA
Electrolysis of Water (Animation)Electrolysis of Water (Animation) http://youtu.be/2t13S-KpGeEhttp://youtu.be/2t13S-KpGeE
Electrolysis of Water (Simple)Electrolysis of Water (Simple) http://youtu.be/HQ9Fhd7P_HAhttp://youtu.be/HQ9Fhd7P_HA
ElectroplatingElectroplating
Electrolysis reaction Electrolysis reaction used to coat aused to coat asubstance with a thinsubstance with a thinlayer of metal.layer of metal.
Often coating is a lessOften coating is a lessreactive metal that isreactive metal that isnot easily oxidized ornot easily oxidized orcorroded.corroded.
ElectroplatingElectroplating Negative ElectrodeNegative Electrode
Is the OBJECT TO BE Is the OBJECT TO BE PLATED PLATED
so the positive metal ions so the positive metal ions would go towards it and be would go towards it and be REDUCED.REDUCED.
It is the CATHODEIt is the CATHODE
Red:Red: Ag Ag++ + 1e- + 1e- AgAg00
ElectroplatingElectroplatingPositive ElectrodePositive Electrode
Made of plating metalMade of plating metal It dissolves into solution as It dissolves into solution as
metal strip gets OXIDIZED.metal strip gets OXIDIZED. It is the ANODEIt is the ANODEThis replenishes the ions for This replenishes the ions for
plating.plating.
Ox:Ox: Ag Ag00 Ag+ + 1e- Ag+ + 1e-
Electroplating Problems Electroplating Problems (Honors)(Honors)
Coulomb = measure of electrical chargeCoulomb = measure of electrical charge
1 mole e- = 96,500 coulombs1 mole e- = 96,500 coulombs
# coulombs = # amps x seconds# coulombs = # amps x seconds
Electroplating Problems Electroplating Problems (Honors)(Honors)
Reduction:Reduction:Happens on object to be platedHappens on object to be plated
Look at Look at ReductionReduction half reaction half reaction
Look at mole relationshipsLook at mole relationshipsbetween electrons and metal atoms.between electrons and metal atoms.
Ex: AgEx: Ag++ + 1e- + 1e- AgAg00
Electroplating Problems Electroplating Problems (Honors)(Honors)
You can now answer questions regarding You can now answer questions regarding the amount of a substance in moles or the amount of a substance in moles or grams that can be electroplated over a grams that can be electroplated over a certain amount of time.certain amount of time.
Electroplating Problems Electroplating Problems (Honors)(Honors)
If 10 amps are run through a CuSOIf 10 amps are run through a CuSO4 4 solution for solution for 5 minutes, calculate the grams of Cu that will plate5 minutes, calculate the grams of Cu that will plateonto the spoon.onto the spoon.
We Know:We Know:1 mole e- = 96,500 coulombs1 mole e- = 96,500 coulombs
# coulombs = # amps x seconds# coulombs = # amps x seconds
Red:Red: Cu Cu+2+2 + 2e- + 2e- CuCu00
1 mole Cu = 63.5 grams1 mole Cu = 63.5 grams
So….Let’s start hereSo….Let’s start here
# coulombs # coulombs = 10 amps x 300 seconds= 10 amps x 300 seconds = 3000 coulombs= 3000 coulombs
3000 coul. x 3000 coul. x 1 mole e-1 mole e- x x 1 mole Cu1 mole Cu x x 63.5g Cu63.5g Cu = .987 grams = .987 grams 96,500 coul 2 mole e- 1 mole Cu96,500 coul 2 mole e- 1 mole Cu
Mole ratio from Reduction half reaction
You Try OneYou Try One
How long will it take to deposit 20 grams ofHow long will it take to deposit 20 grams ofsilver from a solution of AgCl onto a coppersilver from a solution of AgCl onto a coppertray if a current of 5 amps is used?tray if a current of 5 amps is used?
Answer = 3, 574 sec Answer = 3, 574 sec or 59.5 minutes or about 1 houror 59.5 minutes or about 1 hour
You Try OneYou Try One
How many amps are needed to deposit .504g.How many amps are needed to deposit .504g.of Iron in 40 minutes by passing a currentof Iron in 40 minutes by passing a currentthrough a solution of Iron II Sulfate?through a solution of Iron II Sulfate?
Answer: .72 ampsAnswer: .72 amps