CHEM 5013 CHEM 5013 Applied Chemical Applied Chemical

PrinciplesPrinciples

Chapter ThirteenChapter Thirteen

Professor BensleyProfessor BensleyAlfred State CollegeAlfred State College

Chapter ObjectivesChapter Objectives

Define oxidation and reduction.Define oxidation and reduction. Write and balance half-reactions for Write and balance half-reactions for

simple redox processes.simple redox processes. Describe the differences between Describe the differences between

galvanic and electrolytic cells.galvanic and electrolytic cells. Use standard reduction potentials to Use standard reduction potentials to

calculate cell potentials under calculate cell potentials under standard conditions.standard conditions.

Chapter ObjectivesChapter Objectives

Use standard reduction potentials to Use standard reduction potentials to predict the spontaneous direction of predict the spontaneous direction of a redox reaction.a redox reaction.

Calculate the amount of metal Calculate the amount of metal plated, the amount of current plated, the amount of current needed, or the time required for an needed, or the time required for an electrolysis process.electrolysis process.

Chapter ObjectivesChapter Objectives

Distinguish between primary and Distinguish between primary and secondary batteries.secondary batteries.

Describe the chemistry of some Describe the chemistry of some common battery types and explain common battery types and explain why each type of battery is suitable why each type of battery is suitable for a particular application.for a particular application.

Describe at least two common Describe at least two common techniques for preventing corrosion.techniques for preventing corrosion.

Oxidation / ReductionOxidation / Reduction

Oxidation/Reduction Reaction (Redox):

Oxidation:

Reduction:

Oxidation Numbers:

Rule #

Applies To Statement

1 Elements Oxidation number of an element is ALWAYS zero (0).

2 Compounds The sum of the oxidation numbers of the atoms in a compound is ALWAYS zero (0).

3 Monatomic Ions

Oxidation number of a monatomic ion is ALWAYS equal to the charge on the ion.

4 Polyatomic Ions

The sum of the oxidations numbers of the atoms in a polyatomic ion equals the charge on the ion.

5 Oxygen The oxidation number of oxygen is -2 when it is in a compound or a polyatomic ion.

6 Hydrogen The oxidation number of hydrogen is +1 when it is in a compound or a polyatomic ion.

7 Halogens The oxidation number of halogen atoms is -1 when found in a compound or polyatomic ion unless it is combined with oxygen.

Oxidation NumbersOxidation Numbers

Assign oxidation numbers to Carbon in each of Assign oxidation numbers to Carbon in each of the following compounds:the following compounds:

1. Carbon Monoxide1. Carbon Monoxide 2. Carbon Dioxide2. Carbon Dioxide

3. C3. C66HH1212OO66 4. Sodium 4. Sodium BicarbonateBicarbonate

Redox Half-ReactionsRedox Half-Reactions What happens when copper wire is placed in a What happens when copper wire is placed in a

silver nitrate solution? silver nitrate solution?

The solution’s blue color is indicative of what in solution?The solution’s blue color is indicative of what in solution? What are the crystals forming on the surface of the What are the crystals forming on the surface of the

copper wire?copper wire?

Reducing and Oxidizing Reducing and Oxidizing AgentsAgents

0 +1 +2 0Cu(s) + 2Ag+ (aq) Cu2+ (aq) + 2Ag

(s)

Oxidation

Reduction

Reducing Agent

Oxidizing Agent

Reducing Agent:Reducing Agent:

Oxidizing Agent:Oxidizing Agent:

Building a Galvanic CellBuilding a Galvanic Cell Galvanic cell:Galvanic cell:

Galvanic Cell TerminologyGalvanic Cell Terminology

Salt Bridge:Salt Bridge:

Electrodes:Electrodes:

Anode: Anode:

Cathode:Cathode:

anode | anode electrolyte || cathode electrolyte | cathode

Galvanic Cell TerminologyGalvanic Cell Terminology

Cell notation:

EMF (electromotive force) or cell potential:

E0 (cell) =

Cell PotentialsCell Potentials1.1. Calculate the cell potential for the previous Calculate the cell potential for the previous

Copper/Silver cell.Copper/Silver cell.

2.2. Calculate the cell potential for the following Calculate the cell potential for the following galvanic cell.galvanic cell.

Fe(s) | Fe2+ (aq) (1.0M) || Cu 2+ (aq) | Cu (s)

BatteriesBatteries Battery:

Primary Cells:

Secondary Cells:

Primary CellsPrimary Cells

Dry Cell Dry Cell BatteryBattery

1.5 Volts 1.5 Volts Has a finite life Has a finite life

even when not even when not used since used since acidic NHacidic NH44Cl Cl corrodes cancorrodes can

Primary CellsPrimary Cells

Alkaline Dry Alkaline Dry Cell Cell

1.5 Volts 1.5 Volts Longer life Longer life

than dry cell than dry cell but more but more expensiveexpensive

Primary CellsPrimary Cells

Lithium – Lithium – Iodine Battery Iodine Battery

High High resistance, low resistance, low currentcurrent

Used in Used in pacemakers pacemakers and is very and is very reliable (10 reliable (10 yrs)yrs)

Secondary CellsSecondary Cells

Nickel-Nickel-Cadmium Cadmium (NiCad)(NiCad)

Used in Used in calculators, calculators, power tools, power tools, shavers, etc.shavers, etc.

Rechargeable Rechargeable and light.and light.

Secondary CellsSecondary Cells

Lead Storage Lead Storage Cell Cell

Car battery - Car battery - rechargeablerechargeable

Single cell is Single cell is 2V, 6 cells in a 2V, 6 cells in a row so overall row so overall is approx. 12 Vis approx. 12 V

Electrochemistry Electrochemistry ApplicationsApplications

Fuel CellFuel Cell Continuous supply Continuous supply

of fuelof fuel Anode-hydrogen Anode-hydrogen

gas, Cathode-gas, Cathode-oxygen gasoxygen gas

VERY efficientVERY efficient Storage and Storage and

transport of transport of Hydrogen is Hydrogen is limitation.limitation. 2 H2 (g) + O2 (g) 2 H2O (l)

Electrochemistry Electrochemistry ApplicationsApplications

Corrosion – rust – forms only in the Corrosion – rust – forms only in the presence of Opresence of O22 and H and H22O.O.

Electrochemistry Electrochemistry ApplicationsApplications

Galvanizing:

Cathodic Protection:

ElectrolysisElectrolysis Electrolysis:

Passive electrolysis:

Active electrolysis:

Active Electrolysis and Active Electrolysis and ElectroplatingElectroplating

Electroplating:Electroplating:

Electrochemical reactions involved in Electrochemical reactions involved in the plating of silverthe plating of silver

Anode:Anode:

Cathode:Cathode:

Ag(s) + 2 CN-(aq) Ag(CN)2- (aq) + e-

Ag(CN)2- (aq) + e- Ag(s) + 2 CN-(aq)

ElectroplatingElectroplating Current:Current:

The unit of current, the ampere (A), is The unit of current, the ampere (A), is defined as one coulomb per second: defined as one coulomb per second:

1 A = 1 C / s1 A = 1 C / s

Charge = current time

Q = I t

Current and ChargeCurrent and Charge

Faraday’s constant: Faraday’s constant: F = 96,485 C/molF = 96,485 C/mol

Use charge, Faraday’s Constant, and # moles of Use charge, Faraday’s Constant, and # moles of electrons to determine mass of metal plated on object.electrons to determine mass of metal plated on object.

In a copper plating experiment in which copper metal is In a copper plating experiment in which copper metal is deposited from copper(II) ion solution, the system is run for 2.6 deposited from copper(II) ion solution, the system is run for 2.6 hours at a current of 12.0 A. What mass of copper is hours at a current of 12.0 A. What mass of copper is deposited?deposited?