chemcom 2013 2 warm up: determine the name and molar mass of the following compounds. naoh mno 2 h 2...
TRANSCRIPT
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