ChemCom 2013

2

Warm Up: Determine the name and molar mass of the following compounds.

NaOH

MnO2

H2SO4

3

How did you do?

NaOH- 40.00 g/mol, sodium hydroxide

MnO2- 86.94 g/mol, Manganese (IV) oxide

H2SO4 98.09 g/mol, Sulfuric acid

Be sure you go back and review the basics…

ELECTROCHEMISTRYELECTROCHEMISTRY

Electron Transfer ReactionsElectron Transfer ReactionsElectron Transfer ReactionsElectron Transfer Reactions

• Electron transfer reactions are Electron transfer reactions are oxidation-reductionoxidation-reduction

or or redoxredox reactions. reactions.

• Result in the generation of an electric current Result in the generation of an electric current

(electricity) or be caused by imposing an electric (electricity) or be caused by imposing an electric

current. current.

• This field of chemistry is often called This field of chemistry is often called

ELECTROCHEMISTRY.ELECTROCHEMISTRY.

Terminology for Redox Terminology for Redox ReactionsReactions

Terminology for Redox Terminology for Redox ReactionsReactions

• OXIDATIONOXIDATION—loss of electron(s) by a species; —loss of electron(s) by a species; increase in oxidation number; increase in oxygen.increase in oxidation number; increase in oxygen.

• REDUCTIONREDUCTION—gain of electron(s); decrease in —gain of electron(s); decrease in oxidation number; decrease in oxygen; increase oxidation number; decrease in oxygen; increase in hydrogen.in hydrogen.

• OXIDIZING AGENTOXIDIZING AGENT—electron acceptor; species —electron acceptor; species is reduced.is reduced.

• REDUCING AGENTREDUCING AGENT—electron donor; species is —electron donor; species is oxidized.oxidized.

• OXIDATIONOXIDATION—loss of electron(s) by a species; —loss of electron(s) by a species; increase in oxidation number; increase in oxygen.increase in oxidation number; increase in oxygen.

• REDUCTIONREDUCTION—gain of electron(s); decrease in —gain of electron(s); decrease in oxidation number; decrease in oxygen; increase oxidation number; decrease in oxygen; increase in hydrogen.in hydrogen.

• OXIDIZING AGENTOXIDIZING AGENT—electron acceptor; species —electron acceptor; species is reduced.is reduced.

• REDUCING AGENTREDUCING AGENT—electron donor; species is —electron donor; species is oxidized.oxidized.

You can’t have one… without the other!

• Reduction (gaining electrons) can’t happen without an oxidation to provide the electrons.

• You can’t have 2 oxidations or 2 reductions in the same equation. Reduction has to occur at the cost of oxidation

LEOLEO the lion the lion says says GERGER!!

GER!GER!

Another way to remember

•OIL RIG

OXIDATION-REDUCTIONREACTIONSOXIDATION-REDUCTIONREACTIONS

Direct Redox ReactionDirect Redox ReactionOxidizing and reducing agents Oxidizing and reducing agents

in direct contact.in direct contact.

Cu(s) + 2 AgCu(s) + 2 Ag++(aq) ---> Cu(aq) ---> Cu2+2+(aq) + 2 Ag(s)(aq) + 2 Ag(s)

OXIDATION-REDUCTION REACTIONS

OXIDATION-REDUCTION REACTIONS

Indirect Redox ReactionIndirect Redox Reaction

A battery functions by transferring electrons A battery functions by transferring electrons through an external wire from the through an external wire from the

reducing agent to the oxidizing agent.reducing agent to the oxidizing agent.

BatteriesBatteriesBatteriesBatteries• An apparatus that allows a redox An apparatus that allows a redox

reaction to occur by transferring reaction to occur by transferring electrons through an electrons through an external external connectorconnector..

• Product favored reaction Product favored reaction voltaic or galvanic cellvoltaic or galvanic cell results in electric currentresults in electric current

• Reactant favored reaction Reactant favored reaction electrolytic cellelectrolytic cell electric current used to electric current used to

cause cause chemical change.chemical change.

Batteries are voltaic Batteries are voltaic cellscells

Warm Up- Write the formulas

1. Calcium hydroxide

2. Carbon monoxide

3. Iron (III) chloride

4. Copper (II) nitrate

5. Sulfur tetroxide

12

AnodeAnode CathodeCathode

Basic Concepts Basic Concepts of Electrochemical Cellsof Electrochemical Cells

Zn

Zn2+ ions

Cu

Cu2+ ions

wire

saltbridge

electrons

Zn

Zn2+ ions

Cu

Cu2+ ions

wire

saltbridge

electrons

Direct Redox ReactionDirect Redox ReactionDirect Redox ReactionDirect Redox Reaction

Zn metal

Cu2+ ions

Zn metal

Cu2+ ions

With time, Cu plates out onto Zn metal strip, and Zn strip “disappears.”

Corrodes away

With time, Cu plates out onto Zn metal strip, and Zn strip “disappears.”

Corrodes away

•Zn is oxidized Zn is oxidized and is the reducing agent and is the reducing agent Zn(s) ---> ZnZn(s) ---> Zn2+2+(aq) + 2e-(aq) + 2e-

•CuCu2+2+ is reduced is reduced and is the oxidizing agentand is the oxidizing agentCuCu2+2+(aq) + 2e- ---> Cu(s)(aq) + 2e- ---> Cu(s)

•To obtain a useful current, To obtain a useful current, we separate the oxidizing we separate the oxidizing and reducing agents so that and reducing agents so that

electron transferelectron transfer occurs thru occurs thru

an external wire.an external wire.

Zn

Zn2+ ions

Cu

Cu2+ ions

wire

saltbridge

electrons

Zn

Zn2+ ions

Cu

Cu2+ ions

wire

saltbridge

electrons

CHEMICAL CHANGE --->CHEMICAL CHANGE --->ELECTRIC CURRENTELECTRIC CURRENT

CHEMICAL CHANGE --->CHEMICAL CHANGE --->ELECTRIC CURRENTELECTRIC CURRENT

This is accomplished in a This is accomplished in a GALVANICGALVANIC or or VOLTAICVOLTAIC cell. cell.

A group of such cells is called a A group of such cells is called a batterybattery..

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swf

Zn

Zn2+ ions

Cu

Cu2+ ions

wire

saltbridge

electrons

Zn

Zn2+ ions

Cu

Cu2+ ions

wire

saltbridge

electrons

••Electrons travel thru external wire.Electrons travel thru external wire.•Salt bridge Salt bridge allows anions and cationsallows anions and cations to to move move

between electrode compartmentsbetween electrode compartments..

••Electrons travel thru external wire.Electrons travel thru external wire.•Salt bridge Salt bridge allows anions and cationsallows anions and cations to to move move

between electrode compartmentsbetween electrode compartments..

Zn --> ZnZn --> Zn2+2+ + 2e- + 2e- CuCu2+2+ + 2e- --> Cu + 2e- --> Cu

<--Anions<--AnionsCations-->Cations-->

OxidationOxidationAnodeAnodeNegativeNegative

OxidationOxidationAnodeAnodeNegativeNegative

RedReductionuctionCatCathodehodePositivePositive

RedReductionuctionCatCathodehodePositivePositive

RED CATRED CAT

Terms Used for Voltaic CellsTerms Used for Voltaic Cells

OK… that was a lot…

Let’s take a little break and do a cool lab

Do the lab on a separate piece of paper… be sure I get the class set of instructions back!

1. Write the title: Striking it Rich

2. Write the purpose

3. Make a materials list as you do the lab

4. Draw the table that is on the bottom of the page and fill it in as you do the lab.

5. Answer all the questions on the back of the page… you do NOT need to write a conclucing paragraph!

The Procedure

1. Clean 3 pennies using the HCl on the demo desk.

2. Get 4g of granular zinc.3. Get 25mL of Zinc Chloride solution

4. Put the zinc and ZnCl2 in the 100ml beaker.5. Put 2 of the 3 pennies in the beaker and place it

on the hotplate.6. Let the pennies react until they turn a different

color.7. Carefully wave one of your coated pennies over

a flame.

Warm Up (10 minutes)

Make sure that your lab is complete…

Answer all the questions on the back!

Debrief the lab…

Collect….

Science Choices

Another Lab…Yea!

Warm Up

Write and complete the following sentences with these words. Gains, loses, anode, cathode, red, black.

1.Oxidation is when a metal __________ electrons, it takes place at the ________ which is ___________ in color.

2.Reduction is when a metal __________ electrons, it takes place at the ________ which is ___________ in color.

Finish the lab

Turn it in!

Have you ever wondered about the voltage on various batteries?

1.7 Volts 12.6 Volts

CELL POTENTIAL, ECELL POTENTIAL, E

• For Zn/Cu cell, For Zn/Cu cell, potentialpotential is is +1.10 V+1.10 V at 25 ˚C and at 25 ˚C and when [Znwhen [Zn2+2+] and [Cu] and [Cu2+2+] = 1.0 M.] = 1.0 M.

• This is the This is the STANDARD CELL POTENTIAL, ESTANDARD CELL POTENTIAL, Eoo

• a quantitative measure of the tendency of a quantitative measure of the tendency of reactants to proceed to products when all are in reactants to proceed to products when all are in their standard states at 25 ˚C.their standard states at 25 ˚C.

Zn

Zn2+ ions

Cu

Cu2+ ions

wire

saltbridge

electrons

Zn

Zn2+ ions

Cu

Cu2+ ions

wire

saltbridge

electrons

Calculating Cell VoltageCalculating Cell Voltage• Balanced half-reactions can be added Balanced half-reactions can be added

together to get overall, balanced equation.together to get overall, balanced equation.

Zn(s) ---> ZnZn(s) ---> Zn2+2+(aq) + 2e-(aq) + 2e-CuCu2+2+(aq) + 2e- ---> Cu(s)(aq) + 2e- ---> Cu(s)----------------------------------------------------------------------------------------CuCu2+2+(aq) + Zn(s) ---> Zn(aq) + Zn(s) ---> Zn2+2+(aq) + Cu(s)(aq) + Cu(s)

Zn(s) ---> ZnZn(s) ---> Zn2+2+(aq) + 2e-(aq) + 2e-CuCu2+2+(aq) + 2e- ---> Cu(s)(aq) + 2e- ---> Cu(s)----------------------------------------------------------------------------------------CuCu2+2+(aq) + Zn(s) ---> Zn(aq) + Zn(s) ---> Zn2+2+(aq) + Cu(s)(aq) + Cu(s)

If we know EIf we know Eoo for each half-reaction, we for each half-reaction, we could get Ecould get Eoo for net reaction. for net reaction.

Zn/Cu Electrochemical CellZn/Cu Electrochemical Cell

Zn(s) ---> ZnZn(s) ---> Zn2+2+(aq) + 2e-(aq) + 2e- EEoo = +0.76 V = +0.76 VCuCu2+2+(aq) + 2e- ---> Cu(s)(aq) + 2e- ---> Cu(s) EEoo = +0.34 V = +0.34 V

--------------------------------------------------------------------------------------------------------CuCu2+2+(aq) + Zn(s) ---> Zn(aq) + Zn(s) ---> Zn2+2+(aq) + Cu(s) (aq) + Cu(s)

EEoo = +1.10 V = +1.10 V

Cathode, Cathode, positive, positive, sink for sink for electronselectrons

Anode, Anode, negative, negative, source of source of electronselectrons

Zn

Zn2+ ions

Cu

Cu2+ ions

wire

saltbridge

electrons

Zn

Zn2+ ions

Cu

Cu2+ ions

wire

saltbridge

electrons ++

Lead Storage Lead Storage BatteryBattery

Anode (-) Anode (-) EEoo = +0.36 V = +0.36 VPb + HSOPb + HSO44

-- ---> PbSO ---> PbSO44 + H + H++ + 2e- + 2e-

Cathode (+) Cathode (+) EEoo = +1.68 V = +1.68 VPbOPbO22 + HSO + HSO44

-- + 3 H + 3 H++ + 2e- ---> PbSO + 2e- ---> PbSO44 + 2 H + 2 H22OO

Charging a BatteryCharging a BatteryWhen you charge a battery, you are When you charge a battery, you are forcing the electrons backwards (from the forcing the electrons backwards (from the + to the -). + to the -). To do this, you will need a To do this, you will need a higher voltage backwards than forwards. higher voltage backwards than forwards. This is why the ammeter in your car often This is why the ammeter in your car often goes slightly higher while your battery is goes slightly higher while your battery is charging, and then returns to normal.charging, and then returns to normal.

In your car, In your car, the battery charger is the battery charger is called an alternatorcalled an alternator. If you have a . If you have a dead battery, it could be the dead battery, it could be the battery needs to be replaced OR battery needs to be replaced OR the alternator is not charging the the alternator is not charging the battery properly.battery properly.

Dry Cell BatteryDry Cell Battery

Anode (-)Anode (-)

Zn ---> ZnZn ---> Zn2+2+ + 2e- + 2e-

Cathode (+)Cathode (+)

2 NH2 NH44++ + 2e- --> 2 NH + 2e- --> 2 NH33 + H + H22

Alkaline BatteryAlkaline Battery

Nearly same reactions Nearly same reactions as in common dry cell, as in common dry cell, but under basic but under basic conditions.conditions.

Anode (-): Anode (-): Zn + 2 OHZn + 2 OH-- --> ZnO + H --> ZnO + H22O + 2e-O + 2e-Cathode (+): Cathode (+): 2 MnO2 MnO22 + H + H22O + 2e- --> MnO + 2e- --> Mn22OO33 + 2 OH + 2 OH--

Mercury BatteryMercury Battery

Mercury BatteryMercury Battery

Anode:Anode:

Zn is reducing agent under basic Zn is reducing agent under basic conditionsconditions

Cathode:Cathode:

HgO + HHgO + H22O + 2e- ---> Hg + 2 OHO + 2e- ---> Hg + 2 OH--

Ni-Cad BatteryNi-Cad Battery

Anode (-)Anode (-)

Cd + 2 OHCd + 2 OH-- ---> Cd(OH) ---> Cd(OH)22 + 2e- + 2e-

Cathode (+) Cathode (+)

NiO(OH) + HNiO(OH) + H22O + e- ---> Ni(OH)O + e- ---> Ni(OH)22 + +

OHOH--

Ni-Cad BatteryNi-Cad Battery

HH22 as a Fuel as a Fuel

Cars can use electricity generated by HCars can use electricity generated by H22/O/O22

fuel cells.fuel cells.HH22 carried in tanks or generated from carried in tanks or generated from

hydrocarbonshydrocarbons

Warm Up

a. Draw a voltaic cell that would have Magnesium and Iron metal and Mg2+ and Fe2+ ions.

b. Using the table on p.453, determine which metal would be oxidized and which would be reduced.

c. Label the anode and the cathode.

d. Draw an arrow indicating the flow of electrons.

e. Write the half reactions.

f. How would we determine the voltage??

Electrolysis

• describes what happens in an electrolytic cell

• means to use electricity to make chemicals.

• Many elements are “made” by electrolysis

• Pb Al Zn Na K Li H2 Cl2 F2 I2 O2

Aluminum Production by Electrolysis

Name of the Ore imported from (Guinea and Brazil)

Bauxite

Al2O3.3H2O

Heating drives off the waterAl2O3

.3H2O + Heat → Al2O3 + 3H2O

 Melting point of Bauxite is 2045 0C

This is too hot!Cryolite is added Lowers the melting point to 1000 0C

Reduction of water

You cannot reduce Aluminum in water!It must be molten!

CC

DC Power

- +

Al3+

O2-

-

Reduction

Cathode

Al3+ + 3e- → Al(s)

+

Oxidation

Anode

O2- → 1/2O2(g) + 2e-

Liquid Al floats to the top and is removed

Oxygen gas

Al2O3(l)

Cation Cathode Reduction Anion Anode Oxidation

Au+

CN-

Au+

CN-

Electroplating 

Au plating a Cu penny

Electroplating is the process of reducing a metal on to the surface of anotherElectrolyte: Must contain the ion of the metal that platesCathode: The metal to be covered with a new metalAnode: Metal to be plated on top the other metal 

DC Power- +

DC Power- +

Au

+OxidationAnodeAu(s) → Au+ + 1e-

e--ReductionCathodeAu+ + e- → Au(s)

CuCu

AuCN

-ve+ve

stainless steel or Au

Au plated

Copper Ring Gold Plated

Ready for your Quiz???

Zn+2

NO3-

Electroplating 

Zn plating a Penny 

DC Power- +

DC Power- +

Zn

+OxidationAnodeZn(s) → Zn+2 + 2e-

e-

ReductionCathodeZn+2 + 2e- → Zn(s)

$1

e-

Electrorefinning Lead Trail, B.C.Teck 16 mines in BCMajor World Producer of Zn, Cu, Pb, and Coal

The Electrorefinning of Lead  

Electrorefining is the process of purifying a metal by electrolysis.The electrolyte must contain PbImpure metal is oxidized at the anode and pure metal is reduced at the cathode.This is the same as electroplating. 

 

 

DC Power- +

DC Power- +

Pb2+

NO3-

-ReductionCathode

Pb2+ + 2e- → Pb(s)

Cathode: Pure Pb

Anode: Impure Pb

Lead Refinery-Trail

Zn oxidizes

Ag does not oxidize

Pb oxidizes

Au does not oxidizeAt the Anode

The voltage is controlled so that:

Pb2+ reduces

At the Cathode

Zn2+ does not reduce

The voltage is controlled so that:

The Electrorefinning of Lead  Electrorefining is the process of purifying a metal by electrolysis.The electrolyte must contain PbImpure metal is oxidized at the anode and pure metal is reduced at the cathode.This is the same as electroplating. 

 

 

DC Power- +

DC Power- +

Pb2+

NO3-

-ReductionCathode

Pb2+ + 2e- → Pb(s)

Cathode: Pure Pb Anode: Impure Pb

+OxidationAnodeZn(s) → Zn2+ + 2e-

Pb(s) → Pb2+ + 2e-

Zn2+

Au Ag

Solid Au and Cu are released from the anode and fall to the bottom