balance redox rxns:

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.