Balance Redox Rxns: Fe(OH) 3 + [Cr(OH) 4 ] -1 Fe(OH) 2 + CrO 4 -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 E o 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 CuCl 2(aq) is connected to a cell with a Zn electrode in ZnBr 2(aq)

Drill: Determine all species that could react when a cell with an Fe electrode in FeCl 3(aq) is connected to a cell with a Mn electrode in MnCl 2(aq)

Determine all when a cell with a Fe electrode in FeCl 3(aq) is connected to a cell with a Mn electrode in MnCl 2(aq)

Drill: Determine all species that could react when a cell with an Fe electrode in FeCl 2(aq) is connected to a cell with a Mg electrode in MgCl 2(aq)

Determine all when a cell with a Mg electrode in MgCl 2(aq) is connected to a cell with a Au electrode in AuCl 3(aq)

Determine all when a cell with a Cd electrode in CdCl 2(aq) is connected to a cell with a Cu electrode in CuI (aq)

What could happen if you dissolve AuCl 3 in water?

Drill: A voltaic cell is made up of a iron electrode in an aqueous of FeI 2 in one chamber & a copper electrode in an aqueous CuBr 2. 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 FeI 2 in one chamber & a copper electrode in an aqueous CuBr 2. Determine all in this system.

Drill: Determine all species that could react when a cell with an Cr electrode in CrBr 3(aq) is connected to a cell with a Sn electrode in SnI 2(aq)

Determine all when a cell with an chromium electrode in CrBr 3(aq) is connected to a cell with a tin electrode in SnI 2(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: SnO 2 + S 8 SnO + SO 2 in acid

Balance Redox Rxn: N 2 O 3 + K 2 CrO 4 KNO 3 + Cr +3 in base

Balance Redox Rxn: SO + H 2 Cr 2 O 7 H 2 SO 4 + Cr +2

Drill: What is the best reducing agent and the best oxidizing agent on the chart?

Extremely Important Electrochemical Reactions

Lead Sulfate Battery Pb + SO 4 -2  PbSO 4 + 2e - E o = 1.7 V PbO 2 + 4H + + 2e -  PbSO 4 + H 2 O E o = 0.3 V Pb + PbO 2 + 4H + SO 4 -2  2 PbSO 4 + H 2 O E o = 2.0 V

Iron Rusting 2Fe  2Fe e - O 2 + 2H 2 O + 4e -  4OH - 2Fe + O 2 + 2H 2 O  2Fe OH -

Relating Equations  G o =  H o - T  S o  G o = -RTlnK eq  G o = -nF E o

Determine rxn, E o,  G o, & K eq for a voltaic cell with half- cells containing Ni (s) in NiCl 2(aq) & Sn (s) in SnCl 2(aq).

Nernst Equation E = E o - (RT/nF)lnQ for non-standard conditions

Determine the voltage of a cell with a silver electrode in 1.0 M AgNO 3 & a zinc electrode in M ZnCl 2 at 27 o C

Drill: Determine the voltage of a cell with an aluminum electrode in 1.0 M AlCl 3 & a zinc electrode in M ZnCl 2 at 27 o C

Determine the voltage of a cell with an calcium electrode in 1.0 M CaCl 2 & a silver electrode in M AgBr at 27 o C

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 MgI 2(aq) & ZnCl 2(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 CaCl 2(aq) & FeF 2(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 CaCl 2(aq) & FeF 2(aq)

Determine the rxns that takes place when 1.8 V of electricity is passed through two Pt electrodes in ZnCl 2(aq)

Determine the rxns that takes place when 2.0 V of electricity is passed through two Pt electrodes in ZnCl 2(aq)

Determine the voltage of a cell with a silver electrode in 1.0 M AgNO 3 & an iron electrode in 0.10 M FeCl 2 at 27 o C

Drill: Determine all species that could react when electricity is passed through two Pt electrode in a solution containing CaCl 2(aq) & MgF 2(aq)

Determine all the reactions that take place when electricity is passed through two Pt electrode in a solution containing CaCl 2(aq) & MgF 2(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 CuCl 2(aq)

Determine the voltage of a cell with a copper electrode in 0.10 M CuI & a zinc electrode in 1.0 M ZnCl 2 at 27 o C

Determine the voltage of a cell with a silver electrode in 0.10 M AgNO 3 & a zinc electrode in 1.0 M ZnCl 2 at 27 o C

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 CuSO 4 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 AgNO 3

Drill: Calculate the current required to purify 510 kg of aluminum oxide in 5.0 hours

Balance the Rxn KMnO 4 + HCl MnO 2 + KClO 2

Calculate the time required to electroplate 19.7 mg of gold onto a plate by passing 965 mA current through a solution of Au(NO 3 ) 3

Determine the voltage of a cell with a silver electrode in 5.0 M AgNO 3 & an zinc electrode in 0.25 M ZnCl 2 at 27 o C

Determine the rxn that takes place when 1.0 V is passed through two Pt electrodes in a soln containing NaI (aq) & CoCl 2(aq).

Calculate the time required to purify a 204 kg of ore that is 60.0 % Al 2 O 3 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 % Al 2 O 3 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 cm 2 ) by passing 965 mA current through a solution of AuCl 3 (D Au = 20 g/cm 3 )

Current, Mass, Time Formula: Saul’s Rule nFm = MWIt

A voltaic cell with a silver electrode in 0.10 M Ag + & a zinc electrode in 1.0 M Zn +2 at 27 o C is allowed to react for 5.0 mins at 9.65 A. Calculate: E o, E,  G o, & mass increase of the cathode.

A voltaic cell with a gold electrode in M Au +3 & a zinc electrode in 10.0 M Zn +2 at 27 o C is allowed to react for 5.0 hrs at 9.65 A. Calculate: E o, E,  G o, & mass increase of the cathode.