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Balance Redox Rxns:
Fe(OH)3 +
[Cr(OH)4]-1
Fe(OH)2 + CrO4-2
Electro-chemistry
Metallic Conduction
•The flow of electrons through a metal
Ionic Conduction•The movement of ions (electrolytes) through a solution
•Electrolytic Conduct.
Electrode•The surface or point in which oxidation or reduction takes place
Anode•The electrode where oxidation
takes place
•An Ox (-)
Cathode•The electrode where reduction
takes place
•Red Cat (+)
Voltaic or Galvanic Cell
Electrochemical Cell in which:
a spontaneous oxidation-reduction reaction produces electrical energy
Voltaic or Galvanic Cell
Batteries are made up of VCs
Half-Cell•A cell where
either oxidation or reduction takes place
•A half-cell will not work by itself
•Both half-cells are required
•An electrochemical cell must have two
half-cells connected by a salt
bridge
Salt Bridge
1) Allows electrical contact between the two half-cells
2) Prevents mixing of the two half-cell solutions
3) Allows ions to flow maintaining
electrical neutrality
Draw a Voltaic Cell made up of
two half-cells
Drill: Define Each•Oxidation
•Reduction
•Anode
•Cathode
Determining the Redox Rxn & Voltage of an
Electrochemical Cell
1) List all species (molecules,
elements, & ions) (reactants) that
exist in each cell
2a) From the Redox Tables write all
possible half-reactions that could occur in the system
2b ) Record the voltage for each half-rxn. If rxn is reversed, change
sign.
3) Label the oxidation half-rxn that has the highest voltage
4) Label the reduction half-rxn that has the highest voltage
5) Balance the electrons
between the two half-rxns
6a) Add the two half-rxns to
obtain the full electrochemical
reaction
6b) Add the voltage of each
half-rxn to obtain the std. voltage
required
Determine Eo
Zn(s) + 2 Ag+1(aq)
2 Ag(s) + Zn+2(aq)
REDOX Shorthand•Zn|Zn+2||Ag+1|Ag ox
red
•Zn||Zn|Zn+2||Ag+1|Ag||Ag an ox red cat
Drill: Determine Shorthand Rxn & voltage when Cu+1 is reacts with solid
potassium
Voltaic Cell Problems
Determine all when a cell with a Cu electrode
in CuCl2(aq) is connected to a cell with
a Zn electrode in
ZnBr2(aq)
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)
Determine all when a cell with a Fe electrode in FeCl3(aq) is connected
to a cell with a Mn
electrode in MnCl2(aq)
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)
Determine all when a cell with a Mg
electrode in MgCl2(aq) is connected to a cell with
a Au electrode in
AuCl3(aq)
Determine all when a cell with a Cd electrode
in CdCl2(aq) is connected to a cell with a Cu electrode in CuI(aq)
What could happen if you
dissolve AuCl3 in water?
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.
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.
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)
Determine all when a cell with an chromium electrode in CrBr3(aq) is connected to a cell with a tin electrode in
SnI2(aq)
Using the standard Reduction Potential Table, determine the element that is the strongest reducing
agent, & the one that ic the strongest oxidizing agent.
Balance Redox Rxn:
SnO2 + S8
SnO + SO2
in acid
Balance Redox Rxn:
N2O3 + K2CrO4
KNO3 + Cr+3
in base
Balance Redox Rxn:
SO + H2Cr2O7
H2SO4 + Cr+2
Drill: What is the best reducing agent
and the best oxidizing agent on
the chart?
Extremely Important
Electrochemical Reactions
Lead Sulfate BatteryPb + 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
Iron Rusting2Fe 2Fe+2 + 4e-
O2 + 2H2O + 4e- 4OH-
2Fe + O2 + 2H2O 2Fe+2 + 4OH-
Relating Equations
Go = Ho - TSo
Go = -RTlnKeq
Go = -nFEo
Determine rxn, Eo, Go, & Keq for a
voltaic cell with half-cells containing Ni(s)
in NiCl2(aq) & Sn(s)
in SnCl2(aq).
Nernst Equation
E = Eo - (RT/nF)lnQ
for non-standard conditions
• 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
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
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
Typical Dry Cell Battery
Electrolysis•Using electricity to
force a non-spontaneous
electrochemical rxn
Electrolytic Cell
•Chemical cell where electrolysis is being performed
How to determine
everything in an electrolytic cell
1) List all species (molecules,
elements, & ions) (reactants) that
exist in each cell
2a) From the Redox Tables write all
possible half-reactions that could occur in the system
2b ) Record the voltage for each half-rxn. If rxn is reversed, change
sign.
3) Label the oxidation half-rxn that has the highest voltage
4) Label the reduction half-rxn that has the highest voltage
5) Balance the electrons
between the two half-rxns
6a) Add the two half-rxns to
obtain the full electrochemical
reaction
6b) Add the voltage of each
half-rxn to obtain the std. voltage
required
• Determine the rxn that takes place when 1.5 V is passed through two
Pt electrodes in a solution containing
MgI2(aq) & ZnCl2(aq)
• Determine the rxn that takes place when
4.0 V is passed through two Pt electrode in a
solution of NaCl(aq)
Determine the rxn that takes place when
electricity is passed through two Pt
electrode in molten
NaCl
Drill: Determine all species that could react
when electricity is passed through two Pt electrode in a solution containing
CaCl2(aq) & FeF2(aq)
More Electrolytic Problems
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)
Determine the rxns that takes place when 1.8 V of electricity is passed
through two Pt electrodes in ZnCl2(aq)
Determine the rxns that takes place when 2.0 V of electricity is passed
through two Pt electrodes in ZnCl2(aq)
• 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
Drill: Determine all species that could react
when electricity is passed through two Pt electrode in a solution containing
CaCl2(aq) & MgF2(aq)
Determine all the reactions that take place
when electricity is passed through two Pt electrode in a solution containing
CaCl2(aq) & MgF2(aq)
Electroplating & Electro-purifying
Electrolysis• During electrolysis, oxidation
& degradation would occur at the anode while reduction & electroplating would occur at the cathode
Power Supply
Anode Cathode
Impure Metal Pure Metal
Metal salt solution
Standard Unit of Electricity
•Amphere (A)
•1 Amp = 1 coulomb/sec
Unit of Electric Charge
• Coulomb (C)
• The amount of any electroplating can be determined from coulombs because the charge of an electron is known
Faraday’s Constant•The charge of 1 mole of electrons
•~96500 C
Electroplating Formula
•Charge = current x time•Mass can be determined from the charge
• 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)
• 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
• 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
The test on electrochemistry
will be on ____day.
Current Formula• Current = charge/unit time
• Amps = coul/sec
• Amount (mass, volume, moles, etc) can be
determined from the charge
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.
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
Drill: Calculate the current required to purify 510 kg of
aluminum oxide in 5.0 hours
Balance the Rxn
KMnO4 + HCl
MnO2 + KClO2
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
• 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
Determine the rxn that takes place when 1.0 V is passed through
two Pt electrodes in a soln containing NaI(aq)
& CoCl2(aq).
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:
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:
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)
Current, Mass, Time Formula:
Saul’s RulenFm = MWIt
A voltaic cell with a silver electrode in 0.10 M Ag+ & a zinc electrode in 1.0 M Zn+2
at 27oC is allowed to react for 5.0 mins at 9.65 A.
Calculate: Eo, E, Go, & mass increase of the cathode.
A voltaic cell with a gold electrode in 0.0010 M Au+3 &
a zinc electrode in 10.0 M Zn+2 at 27oC is allowed to react for 5.0 hrs at 9.65 A.
Calculate: Eo, E, Go, & mass increase of the cathode.