oxidation and reduction reactions. oxidation (read only) original definition: when substances...

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) reactions

CHCH44(g) + 2O(g) + 2O22(g) (g) COCO22(g) + 2H(g) + 2H22O(l)O(l)

All “rusting” reactionsAll “rusting” reactions

4Fe(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 produced

products that were “reduced” in mass becauseproducts that were “reduced” in mass because

gas 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 ELECTRONSELECTRONS

during 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 towards

what 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 Problems

http://www.usca.edu/chemistry/genchem/oxhttp://www.usca.edu/chemistry/genchem/oxnumb.htmnumb.htm

Animation of Oxidation and ReductionAnimation of Oxidation and Reduction

http://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


SynthesisSynthesis: : YESYES

00 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


Combustion:Combustion:

CHCH44 + 2O + 2O22 COCO22 + 2H + 2H2200

Single Replacement:Single Replacement:

Zn + CuClZn + CuCl22 ZnClZnCl22 + Cu + Cu


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



Double Replacement:Double Replacement:

AgNOAgNO33 + LiCl + LiCl AgCl + LiNO AgCl + LiNO33


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 ions

do not change!do not change!

Writing Half ReactionsWriting Half Reactions

Redox Reactions are composed of two partsRedox Reactions are composed of two parts

or 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 Reactions

0 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


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 elements

changing 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 Metals

the metal gets oxidizedthe metal gets oxidized

forming 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 negative

terminal of a battery.terminal of a battery.

Gold doesn’t rust…Why?

Photograph DevelopmentPhotograph Development involves oxidation and involves oxidation and

reduction of silver atoms and ionsreduction of silver atoms and ions

BleachBleach acts on acts on

stains by oxidizingstains by oxidizing

them, getting reduced them, getting reduced

in the processin the process

ExplosivesExplosives form form

neutral 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 substance

travel towards substance being reduced.travel towards substance being reduced.

Traveling electrons moveTraveling electrons move

through “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 metal

above to ion ofabove to ion of

metal 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 Ions

External WireExternal Wire

Salt BridgeSalt Bridge

Electrons need to flow in a “circuit” thatElectrons need to flow in a “circuit” that

is connected.is connected.

External WireExternal Wire: :

allows electrons to flowallows electrons to flow

between 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 oxidized

ZnZn

Ion of metal below reducedIon of metal below reduced

CuCu+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 to

positive electrode.positive electrode.

Negative electrode: ZnNegative electrode: Zn

Positive 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

RememberRemember

AN 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 towards

the 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 has

reached 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 Table

Find 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” a

compound into it’s neutral elementscompound into it’s neutral elements

An outside electrical source provides electronsAn outside electrical source provides electrons

to force a to force a non-spontaneous redox reactionnon-spontaneous redox reaction to to

occur.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 electrode

Making 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 of

opposite chargeopposite charge

At neg. electrodeAt neg. electrode

electrons are gainedelectrons are gained by ion by ion

(reduction at CATHODE)(reduction at CATHODE)

At positive electrodeAt positive electrode

electrons are lostelectrons are lost by ion by ion

(oxidation at ANODE)(oxidation at ANODE)

What is Oxidized/Reduced?What is Oxidized/Reduced?

RememberRemember

AN 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 Equation

Rxn 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 total

voltage 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.


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


Positive ElectrodePositive ElectrodeMade 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


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 relationships

between electrons and metal atoms.between electrons and metal atoms.

Ex: AgEx: Ag++ + 1e- + 1e- AgAg00


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.


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 of

silver from a solution of AgCl onto a coppersilver from a solution of AgCl onto a copper

tray 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 current

through a solution of Iron II Sulfate?through a solution of Iron II Sulfate?

Answer: .72 ampsAnswer: .72 amps

oxidation and reduction reactions. oxidation (read only) original definition: when substances...

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