{ unit 7: redox & electrochemistry. what information does the oxidation number give you?
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Unit 7: Redox &
Electrochemistry
What information does the oxidation number give you?
• Electrical production (batteries, fuel cells)
Why electrochemistry?REDOX reactions are important in …
• Purifying metals (e.g. Al, Na, Li)
• Producing gases (e.g. Cl2, O2, H2)
• Electroplating metals
• Protecting metals from corrosion• Balancing complex chemical equations• Sensors and machines (e.g. pH meter)
C3H8O + CrO3 + H2SO4 Cr2(SO4)3 + C3H6O + H2O
REDOX stands for REDuction/OXidation
Oxidation is often thought of as a combination of a substance with oxygen (rusting, burning)
Oxidation refers to a loss of e-
Reduction refers to a gain of e-
What is Redox?
Loss Electrons = Oxidation
Gain Electrons = Reduction
Remember: LEO the lions
says GERRRRRR!
Reactions
What is happening to the Fe atom?
Fe is going from 0 to +3 oxidation #
It must be losing electrons
Loss of Electrons = Oxidation
In conclusion, the iron atom is being oxidized
Reactions
What is happening to the Sulfur atom?
S is going from 0 to -2 oxidation #
It must be gaining electrons
Gain of Electrons = Reduction
In conclusion, the sulfur atom is being reduced
Oxidation Numbers- the charge an atom would have if the electrons belonged to the more EN atom
- there are a few rules to help us out
1. FREE ELEMENTSALWAYS HAVE AN OXIDATION NUMBER OF ZERO
Na Na0
H2 H20
F2 F20
Oxidation Numbers- the charge an atom would have if the electrons belonged to the more EN atom
4. HYDROGEN
H is ALWAYS +1 (for us) Disclaimer – there are compounds where H has a -1 oxidation number, but we don’t deal with them at this level of chemistry.
Oxidation Numbers- the charge an atom would have if the electrons belonged to the more EN atom
5. OXYGEN
O is ALWAYS -2 (for us)
Oxidation Numbers- the charge an atom would have if the electrons belonged to the more EN atom
2. SIMPLE IONSOXIDATION NUMBER = THE CHARGE AN ION WOULD MAKE
Sodium ion Na+1
Calcium ion Ca+2
Sulfur ion
N-3Nitrogen ion
S-2
Oxidation Numbers- the charge an atom would have if the electrons belonged to the more EN atom
3. COMPOUNDSTHE SUM OF ALL OXIDATION NUMBERS WILL EQUAL ZERO
NaCl Na+1Cl-1
AsI5 As+5I5
-1
Cu(NO3)2
H2+1Cr2
+6 O7
-2H2Cr2O7
Cu+2(N+5O3-2)2
Oxidation Numbers- the charge an atom would have if the electrons belonged to the more EN atom
5. POLYATOMIC IONSTHE SUM OF OXIDATION NUMBERS WILL EQUAL THE CHARGE OF THAT ION
(SO4)-2 (S+6O4-2)-2
(NO3)- (N+5O3-2)-
(Cr2O4)-2 (Cr2+3O4)-2
Oxidation NumbersDo the five problems on your notes sheet
a. Cr2O3
b. H2Cr2O7
c. AsCl5
d. KCl
e. Mg(OH)2
What things are conserved during a chemical reaction?
What is reduced/oxidized?Identify in the following reactions what is
oxidized and what is reduced
2K + Cl2 2KCl
K0 – goes from 0 to +1, it is oxidized
Cl0 – goes from 0 to -1, it is reduced
PracticeIdentify in the following reactions what is
oxidized and what is reduced
2NaCl + 3SO3 Cl2 + SO2 + Na2S2O7
Cl-1 – goes from -1 to 0, it is oxidized
S+6 – goes from +6 to +4, it is reduced
PracticeIdentify in the following reactions what is
oxidized and what is reduced
Zn + Pb+2(aq) Zn+2
(aq) + Pb
Zn0 – goes from 0 to +2, it is oxidized
Pb+2 – goes from +2 to 0, it is reduced
a. C + H2SO4 CO2 + SO2 + H2O
b. HNO3 + HI NO + I2 + H2O
c. KMnO4 + HCl MnCl2 + Cl2 + H2O +
KCl
d. Sb + HNO3 Sb2O5 + NO + H2O
e. HCl + MnO2 MnCl2 + H2O + Cl2
a. C + H2SO4 CO2 + SO2 + H2O
b. HNO3 + HI NO + I2 + H2O
c. KMnO4 + HCl MnCl2 + Cl2 + H2O + KCl
d. Sb + HNO3 Sb2O5 + NO + H2O
e. HCl + MnO2 MnCl2 + H2O + Cl2
1. C + 2Cl2 CCl4
Ox –
Red –
2. H2 + Cl2 2HCl
Ox –
Red –
3. 2P + 3Cl2 2PCl3
Ox –
Red –
4. C + H2O CO + H2
Ox –
Red –
5. Fe + 3Cl2 2FeCl2
Ox –
Red –
6. 2Al + 3Br2 2AlBr3
Ox –
Red –
7. Pb + 2HCl PbCl2 + H2
Ox –
Red –
8. SiO2 + 2C Si + 2CO
Ox –
Red –
9. CO2 + 2Mg 2MgO + C
Ox –
Red –
10. H2SO4 + Zn ZnSO4 + H2
Ox –
Red -
Identify what atom is oxidized and what atom is
reduced:
Fe + 2HCl FeCl2 + H2
HALF REACTIONS
Cu + AgNO3 Cu(NO3)2 + Ag
Reduction:
Write both half reactions for the following reaction:
Oxidation:
Ag+ Ag
Cu Cu+2 + 2e-
Cu Cu+2
Ag+ + 1e- Ag
Cu - 2e- Cu+2
HALF REACTIONS
HNO3 + I2 HIO3 + NO2
Reduction:
Write both half reactions for the following reaction:
Oxidation:
N+5 N+4
I20 2I+5 + 10e-
I20 I+5
N+5 + 1e- N+4
I20 - 10e- 2I+5
Sn + AgNO3 Sn(NO3)2 + Ag
Reduction:
Write both half reactions for the following reaction:
Oxidation:
Ag+1 Ag0
Sn0 Sn+2 + 2e-
Sn0 Sn+2
Ag+1 + 1e- Ag0
Sn0 - 2e- Sn+2
Half Reactions
Redox Lab
Al + CuCl2
Mass
GFM
Moles
Cu + AlCl32 3 3 2
If you were to react Cu and Nickel(II) Chloride what would the products be? How much metal could you make if you
started with 2.00g of Cu?
Oxidizing and Reducing Agents
Oxidizing Agent
Reducing Agent
- causes the oxidation of another atom
- oxidation number decreases
- causes the reduction of another atom
- oxidation number increases
Ca + Cl2 CaCl2What is the O.A.? What is the R.A.?
Cl
Ca
- it is actually the atom that is REDUCED
- it is actually the atom that is OXIDIZED
PRACTICE
4HCl + MnO2 MnCl2 + 2H2O + Cl2
Oxidizing Agent:
Reducing Agent:
Mn+4
Cl-
In the equation below, identify what is oxidized what is reduced. Also identify the oxidizing and reducing agent.
Reduced:
Oxidized: Cl-
Mn+4
Deals with chemical reactions that either produce electricity or need electricity to occur!
There are 2 types of ELECTROCHEMICAL CELLS.
Some things that are the same for both types of cells:
1. The RED CAT GETS FAT!
2. Electrons always flow from the anode to the cathode!
Anorexic Ox
Electrochemical Reactions
Cu
Cu electrode
Zn
Zn electrodeLose e- (Table J)
Oxidized
Anode (-)
Gains e- (Table J)
Reduced
Cathode(+)
2e-
2e-
2e- 2e- 2e- 2e- 2e- 2e- 2e-
2e-
2e-
Zn+2
Zn+2 Cu+2
Cu+2
ZnSO4 CuSO4
Will this go on forever?
Half Reactions
Cu
Cu electrode
Zn
Zn electrodeLose e- (Table J)
Oxidized
Anode (-)
Gains e- (Table J)
Reduced
Cathode(+)
Zn+2
ZnSO4 CuSO4
Will this go on forever?
Half Reactions
ZnSO4 CuSO4
Cu
Cu electrode
Zn
Zn electrode
Lose e- (Table J)
Oxidized
Anode (-)
Gains e- (Table J)
Reduced
Cathode(+)
Na+Cl- Na+
Na+
Na+
Cl-
Cl-
Cl- Na+
Cl-
Na+
Cl-
2e-
2e-
Zn+2
Zn+2
2e- 2e- 2e-
2e-
Cu+2
Cu+2
2Cl-
2Na+
Electrochemistry
Half Reactions
In the reaction below, identify what is the oxidizing agent and
the reducing agent.
Ca + H2O CaO + H2
ZnSO4 CuSO4
Cu
Cu electrode
Zn
Zn electrode
Lose e- (Table J)
Oxidized
Anode (-)
Gains e- (Table J)
Reduced
Cathode(+)
Na+Cl- Na+
Na+
Na+
Cl-
Cl-
Cl- Na+
Cl-
Na+
Cl-
2e-
2e-
Zn+2
Zn+2
2e- 2e- 2e-
2e-
Cu+2
Cu+2
2Cl-
2Na+
Electrochemistry
Summary:
1. Voltaic Cells – are spontaneous reactions
2. Electrons travel through the wire from more reactive metal to the less reactive metal (Table J)
3. Salt Bridge – permits the flow of ions
4. Red Cat gets fat!
Electrochemistry
These are NOT spontaneous reactions – they are forced by the addition of electricity!
Occur within one container, not two separate cells!
These reactions are used to plate metals, purify metals and separate compounds.
Electrochemistry
Sn
Fe
Electrochemistry
CathodeBecomes negative
Picks up + ions from solution
Gets plated with the metal ion from the
solution
Anode
Becomes positive
Loses positive ion (Sn+2) to solution
During a laboratory activity, a student reacted a piece of zinc
with 0.1M HCl(aq). Based on Reference Table J, identify one
metal that does not react spontaneously with HCl(aq).
K
K electrode
Fe
Fe electrode
NaBr
K+1Fe+2
Write out the oxidation and reduction half reactions for the voltaic cell below. (Do not need drawing in notes)
Electrochemical Cell Differences
spontaneous
non-spontaneous
Anode - negative Anode - positive
Electrochemistry
Needs two containers
Needs one container
Packet Review16.
K
K electrode
Fe
Fe electrode
NaBr
K+1Fe+2
Packet Review16.
Ag
Ag electrode
Al
Al electrode
Na2SO4
Al+3 Ag+1
Cu
Zn
Anode Cathode
Electrons ALWAYS flow from Anode to Cathode
Becomes negative
Picks up + ions from solution
Cu+2
Gets plated with the metal ion from the
solution
Becomes positive
Loses positive ion (Cu+2) to solution
Electrochemistry
Electrochemistry
And review packet
Cu
Zn
Anode Cathode
Electrons ALWAYS flow from Anode to Cathode
Becomes negative
Picks up + ions from solution
Cu+2
Gets plated with the metal ion from the
solution
Becomes positive
Loses positive ion (Cu+2) to solution
Electrochemistry
Electrochemistry
Balancing Net Ionic Equations
Done on the board
Electrochemistry
Electrolysis Simulation
Ionic equation balancing
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Balancing equations using oxidation numbers
C3H8O + CrO3 + H2SO4 Cr2(SO4)3 + C3H6O + H2O
BALANCING REACTIONS- conservation of mass and charge
- we must make sure that the e- that one atom loses must equal the e- that another atom gains
HNO3 + I2 HIO3 + NO2 + H2O
Try to balance this one:
BALANCING REACTIONSHNO3 + I2 HIO3 + NO2 + H2O
1. Assign ox #’s, write ½ reactions and cross out spectators
N+5 + 1e- N+4
I20 - 5e- I+5
2. Balance each ½ reaction with respect to atoms and then e-
N+5 + 1e- N+4
I20 - 10e- 2I+5
10 )(
3. Distribute to all parts of the ½ reaction
1 )(
10N+5 + 10e- 10N+4
I20 - 10e- 2I+5
BALANCING REACTIONS3. Carry everything down and cross out e-
10N+5 + 10e- 10N+4
I20 - 10e- 2I+5
10N+5 + I20 10N+4 + 2I+5
4. Put coefficients back into equation and balance what is left.
10HNO3 + 1I2 10HIO3 + 2NO2 + H2O4
BALANCING REACTIONSSb + HNO3 Sb2O5 + NO + H2O
1. Assign ox #’s, write ½ reactions and cross out spectators
Sb0 Sb2+5 + 5e-
N+5 + 3e- N+2
2. Balance each ½ reaction with respect to atoms and then e-
3 )(
3. Distribute to all parts of the ½ reaction
10 )(
6Sb0 3Sb2+5 + 30e-
10N+5 + 30e- 10N+2
2Sb0 Sb2+5 + 10e-
N+5 + 3e- N+2
Most missed Part 2 Questions1. You have a voltaic cell with copper and aluminum as the electrodes. As the cell operates, the mass of the Al electrode decreases. Explain, in terms of particles, why this decrease in mass occurs.
2. Explain, in terms of electrical energy, how the operation of a voltaic cell differs from the operation of an electrolytic cell used in the Hall process. Include both the voltaic cell and the electrolytic cell in your answer.
3. Explain, in terms of ions, why molten cryolite conducts electricity.
[Cryolite = Na3AlF6]
6Sb + 10HNO3 3Sb2O5 + 10NO + H2O
6Sb0 3Sb2+5 + 30e-
10N+5 + 30e- 10N+2
BALANCING REACTIONS3. Carry everything down and cross out e-
6Sb0 +10N+5 3Sb2+5 + 10N+2
4. Put coefficients back into equation and balance what is left.
5
Balance the following
S + HNO3 SO2 + NO + H2O
The Statue of Liberty is made of an iron framework covered by copper metal. Over time, a thin green layer(patina) forms on the outside. Where the iron came into contact with the copper a
reaction occurred where the iron was oxidized. Why did this happen? Use
your Reference Tables.
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