Balance Redox Rxns: Fe(OH) 3 + [Cr(OH) 4 ] -1 Fe(OH) 2 + CrO 4 -2 in base.

Balance Redox Rxns: Fe(OH)3 + [Cr(OH)4]-1

Fe(OH)2 + CrO4-2

in base

Electrochemistry

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

Half-Cell•A cell where only

oxidation or only reduction takes

place

•An electrochemical cell must have two

half-cells connected by a salt

bridge

•A half-cell will not work by itself

•Both half-cells are required

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

Determining the Redox Rxn & Voltage of an

Electrochemical Cell

Identify all molecules & ions

(reactants) that exist in the

electrolytic cell

1) Determine all possible half-reactions that

could occur in the system

2 ) Look up each half-rxn from

the Std. Redox Tables

3) Record each half-rxn & its

standard voltage

4) Save the oxidation half-rxn that has the highest voltage

5) Save the reduction half-rxn that has the highest voltage

6) Balance the electrons

between the two half-rxns

7) Add the two half-rxns to

obtain the full electrochemical

reaction

7) Add the voltage of each half-rxn to

obtain the std. voltage required

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)

Determine all when a cell with a Fe electrode in FeCl3(aq) is connected

to a cell with a Mn

electrode in MnCl2(aq)

Determine all when a cell with a Mg electrode in

Mg(NO3)2(aq) is connected to a cell with a Au

electrode in Au(NO3)3 (aq)

Electrolysis•Using electricity to

force a non-spontaneous

electrochemical rxn

Electrolytic Cell

•Chemical cell where electrolysis is being performed

How to determine the Redox Rxn &

voltage of an Electrolytic Cell

Identify all molecules & ions

(reactants) that exist in the

electrolytic cell

1) Determine all possible half-reactions that

could occur in the system

2 ) Look up each half-rxn from

the Std. Redox Tables

3) Record each half-rxn & its

standard voltage

4) Save the oxidation half-rxn that has the highest voltage

5) Save the reduction half-rxn that has the highest voltage

6) Balance the electrons

between the two half-rxns

7) Add the two half-rxns to

obtain the full electrochemical

reaction

7) 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

2.5 V is passed through two Pt electrode in a

solution of NaCl(aq)

0

• Determine the rxn that takes place when 2.0 V&

9.65 A is passed for 2.5 Hrs through two Pt electrodes in

a solution containing

MnBr2(aq) & AlF3(aq)

Relating Equations

Go = Ho - TSo

Go = -RTlnKeq

Go = -nFEo

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 & an iron

electrode in 0.10 M

Fe(NO3)2 at 27oC

• Determine the voltage of a cell with a silver

electrode in 1.0 M AgNO3 & a zinc

electrode in 0.010 M

Zn(NO3)2 at 27oC

• Determine the voltage of a cell with a copper

electrode in 0.10 M CuNO3 & a zinc

electrode in 1.0 M

Zn(NO3)2 at 27oC

Electroplating & Electro-purifying

Electrolysis• During electrolysis, oxidation

& degradation would occur at the anode while reduction & electroplating would occur at the cathode

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 onto the cathode when a 96.5 mAmp current is applied to a solution of

AgNO3

Calculate the current required to purify 510 kg

of aluminum oxide in 5.0 hours

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

Calculate the time required to gold plate a 2.0 mm layer onto a 250 cm2 by passing 965 mA current

through a solution of Au(NO3)3

(DAu = 20 g/cm3)

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:

Calculate the time required to purify a 32 kg of ore that

is 75.0 % Fe2O3 by applying a 9.65 kA current through molten ore sample:

• Determine the voltage of a cell with a silver

electrode in 5.0 M AgNO3 & an zinc

electrode in 0.25 M

Zn(NO3)2 at 27oC