Electrochemistry

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Balance Redox Rxns

• Fe(OH)3
• Cr(OH)4-1
• Fe(OH)2 CrO4-2

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Electro-chemistry
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Metallic Conduction

• The flow of electrons through a metal

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Ionic Conduction

• The movement of ions (electrolytes) through a
  solution
• Electrolytic Conduct.

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Electrode

• The surface or point in which oxidation or
  reduction takes place

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Anode

• The electrode where oxidation takes place
• An Ox (-)

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Cathode

• The electrode where reduction takes place
• Red Cat ()

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Voltaic or Galvanic Cell

• Electrochemical Cell in which

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a spontaneous oxidation-reduction reaction
produces electrical energy
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Voltaic or Galvanic Cell

• Batteries are made up of VCs

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Half-Cell

• A cell where either oxidation or reduction takes
  place

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• A half-cell will not work by itself
• Both half-cells are required

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• An electrochemical cell must have two half-cells
  connected by a salt bridge

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Salt Bridge

• ) Allows electrical contact between the two
  half-cells

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• ) Prevents mixing of the two half-cell solutions

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• ) Allows ions to flow maintaining electrical
  neutrality

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Draw a Voltaic Cell made up of two half-cells
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Drill Define Each

• Oxidation
• Reduction
• Anode
• Cathode

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Determining the Redox Rxn Voltage of an
Electrochemical Cell
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1) List all species (molecules, elements, ions)
(reactants) that exist in each cell
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2a) From the Redox Tables write all possible
half-reactions that could occur in the system
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• b ) Record the voltage for each half-rxn. If rxn
  is reversed, change sign.

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3) Label the oxidation half-rxn that has the
highest voltage
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4) Label the reduction half-rxn that has the
highest voltage
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5) Balance the electrons between the two
half-rxns
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6a) Add the two half-rxns to obtain the full
electrochemical reaction
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6b) Add the voltage of each half-rxn to obtain
the std. voltage required
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Determine Eo

• Zn(s) 2 Ag1(aq)
• 2 Ag(s) Zn2(aq)

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REDOX Shorthand

• ZnZn2Ag1Ag ox red
• ZnZnZn2Ag1AgAg an ox red cat
  

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Drill Determine Shorthand Rxn voltage when
Cu1 is reacts with solid potassium
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Voltaic Cell Problems
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• Determine all when a cell with a Cu electrode in
  CuCl2(aq) is connected to a cell with a Zn
  electrode in ZnBr2(aq)

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• Drill Determine all species that could react
  when a cell with an Fe electrode in FeCl3(aq) is
  connected to a cell with a Mn electrode in
  MnCl2(aq)

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• Determine all when a cell with a Fe electrode in
  FeCl3(aq) is connected to a cell with a Mn
  electrode in MnCl2(aq)

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• Drill Determine all species that could react
  when a cell with an Fe electrode in FeCl2(aq) is
  connected to a cell with a Mg electrode in
  MgCl2(aq)

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• Determine all when a cell with a Mg electrode in
  MgCl2(aq) is connected to a cell with a Au
  electrode in AuCl3(aq)

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• Determine all when a cell with a Cd electrode in
  CdCl2(aq) is connected to a cell with a Cu
  electrode in CuI(aq)

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What could happen if you dissolve AuCl3 in water?
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Drill

• A voltaic cell is made up of a iron
  electrode in an aqueous of FeI2 in one chamber
  a copper electrode in an aqueous CuBr2. Determine
  all of the substances that could be reactants in
  this system.

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A voltaic cell is made up of a iron electrode in
an aqueous of FeI2 in one chamber a copper
electrode in an aqueous CuBr2. Determine all in
this system.
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• Drill Determine all species that could react
  when a cell with an Cr electrode in CrBr3(aq) is
  connected to a cell with a Sn electrode in
  SnI2(aq)

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• Determine all when a cell with an chromium
  electrode in CrBr3(aq) is connected to a cell
  with a tin electrode in SnI2(aq)

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Using the standard Reduction Potential Table,
determine the element that is the strongest
reducing agent, the one that ic the strongest
oxidizing agent.
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Balance Redox Rxn

• SnO2 S8
• SnO SO2
• in acid

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Balance Redox Rxn

• N2O3 K2CrO4
• KNO3 Cr3
• in base

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Balance Redox Rxn

• SO H2Cr2O7
• H2SO4 Cr2

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Drill What is the best reducing agent and the
best oxidizing agent on the chart?
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Extremely Important Electrochemical Reactions
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Lead Sulfate Battery

• Pb SO4-2 ??
• PbSO4 2e- Eo 1.7 V
• PbO2 4H 2e- ??
• PbSO4 H2O Eo 0.3 V
• Pb PbO2 4H SO4-2 ??
• 2 PbSO4 H2O Eo 2.0 V

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Iron Rusting

• 2Fe ?? 2Fe2 4e-
• O2 2H2O 4e- ?? 4OH-
• 2Fe O2 2H2O ?? 2Fe2 4OH-

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Relating Equations

• DGo DHo - TDSo
• DGo -RTlnKeq
• DGo -nFEo

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Determine rxn, Eo, DGo, Keq for a voltaic cell
with half-cells containing Ni(s)in NiCl2(aq)
Sn(s)in SnCl2(aq).
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Nernst Equation

• E Eo - (RT/nF)lnQ
• for non-standard conditions

54

• Determine the voltage of a cell with a silver
  electrode in 1.0 M AgNO3 a zinc electrode in
  0.010 M ZnCl2 at 27oC

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Drill Determine the voltage of a cell with an
aluminum electrode in 1.0 M AlCl3 a zinc
electrode in 0.010 M ZnCl2 at 27oC
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Determine the voltage of a cell with an calcium
electrode in 1.0 M CaCl2 a silver electrode in
0.010 M AgBr at 27oC
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Typical Dry Cell Battery
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Electrolysis

• Using electricity to force a non-spontaneous
  electrochemical rxn

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Electrolytic Cell

• Chemical cell where electrolysis is being
  performed

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How to determine everything in an electrolytic
cell
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1) List all species (molecules, elements, ions)
(reactants) that exist in each cell
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2a) From the Redox Tables write all possible
half-reactions that could occur in the system
63

• b ) Record the voltage for each half-rxn. If rxn
  is reversed, change sign.

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3) Label the oxidation half-rxn that has the
highest voltage
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4) Label the reduction half-rxn that has the
highest voltage
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5) Balance the electrons between the two
half-rxns
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6a) Add the two half-rxns to obtain the full
electrochemical reaction
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6b) Add the voltage of each half-rxn to obtain
the std. voltage required
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• Determine the rxn that takes place when 1.5 V is
  passed through two Pt electrodes in a solution
  containing MgI2(aq) ZnCl2(aq)

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• Determine the rxn that takes place when
• 4.0 V is passed through two Pt electrode in a
  solution of NaCl(aq)

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Determine the rxn that takes place when
electricity is passed through two Pt electrode
in molten NaCl
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Drill Determine all species that could react
when electricity is passed through two Pt
electrode in a solution containing CaCl2(aq)
FeF2(aq)
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More Electrolytic Problems
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Determine the rxns that take place when 2.0 V of
electricity is passed through two Pt electrode
in a solution containing CaCl2(aq) FeF2(aq)
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Determine the rxns that takes place when 1.8 V
of electricity is passed through two Pt
electrodes in ZnCl2(aq)
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Determine the rxns that takes place when 2.0 V
of electricity is passed through two Pt
electrodes in ZnCl2(aq)
77

• Determine the voltage of a cell with a silver
  electrode in 1.0 M AgNO3 an iron electrode in
  0.10 M FeCl2 at 27oC

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Drill Determine all species that could react
when electricity is passed through two Pt
electrode in a solution containing CaCl2(aq)
MgF2(aq)
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Determine all the reactions that take place when
electricity is passed through two Pt electrode
in a solution containing CaCl2(aq) MgF2(aq)
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Electroplating Electro-purifying
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Electrolysis

• During electrolysis, oxidation degradation
  would occur at the anode while reduction
  electroplating would occur at the cathode

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Power Supply
Metal salt solution
Pure Metal
Impure Metal
Anode
Cathode
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Standard Unit of Electricity

• Amphere (A)
• 1 Amp 1 coulomb/sec

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Unit of Electric Charge

• Coulomb (C)
• The amount of any electroplating can be
  determined from coulombs because the charge of an
  electron is known

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Faradays Constant

• The charge of 1 mole of electrons
• 96500 C

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Electroplating Formula

• Charge current x time
• Mass can be determined from the charge

87

• Determine the mass of copper plated onto the
  cathode when 9.65 mA is passed for 2.5 Hrs
  through two Cu electrodes in a solution
  containing CuCl2(aq)

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• Determine the voltage of a cell with a copper
  electrode in 0.10 M CuI a zinc electrode in 1.0
  M ZnCl2 at 27oC

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• Determine the voltage of a cell with a silver
  electrode in 0.10 M AgNO3 a zinc electrode in
  1.0 M ZnCl2 at 27oC

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The test on electrochemistry will be on ____day.
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Current Formula

• Current charge/unit time
• Amps coul/sec
• Amount (mass, volume, moles, etc) can be
  determined from the charge

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Calculate the mass of copper plated onto the
cathode when a 9.65 mAmp current is applied to a
solution of CuSO4 for 5.0 minutes.
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Calculate the years required to plate 216 kg of
silver onto the cathode when a 96.5 mAmp current
is applied to a solution of AgNO3
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Drill Calculate the current required to purify
510 kg of aluminum oxide in 5.0 hours
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Balance the Rxn

• KMnO4 HCl
• MnO2 KClO2

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Calculate the time required to electroplate 19.7
mg of gold onto a plate by passing 965 mA current
through a solution of Au(NO3)3
97

• Determine the voltage of a cell with a silver
  electrode in 5.0 M AgNO3 an zinc electrode in
  0.25 M ZnCl2 at 27oC

98
Determine the rxn that takes place when 1.0 V is
passed through two Pt electrodes in a soln
containing NaI(aq) CoCl2(aq).
99
Calculate the time required to purify a 204 kg of
ore that is 60.0 Al2O3 by applying a 965 kA
current through molten ore sample
100
Drill Aluminum ore is purified by electrolysis.
Calculate the time required to purify a 51 kg of
ore that is 75.0 Al2O3 by applying a 9.65 kA
current through molten ore sample
101
Calculate the time required to gold plate a 0.20
mm layer onto a plate(SA 750 cm2) by passing
965 mA current through a solution of AuCl3(DAu
20 g/cm3)
102
Current, Mass, Time FormulaSauls Rule

• nFm MWIt

103
A voltaic cell with a silver electrode in 0.10 M
Ag a zinc electrode in 1.0 M Zn2 at 27oC is
allowed to react for 5.0 mins at 9.65
A.Calculate Eo, E, DGo, mass increase of the
cathode.
104
A voltaic cell with a gold electrode in 0.0010 M
Au3 a zinc electrode in 10.0 M Zn2 at 27oC is
allowed to react for 5.0 hrs at 9.65
A.Calculate Eo, E, DGo, mass increase of the
cathode.