1
UNIT 5 OXIDATION AND REDUCTION (pg 652 )
Day 1
Definitions :
Oxidation -
of electrons by an atom
Reduction -
of electrons by an atom
* Memory aid - LEO THE LION SAYS GER OR OIL RIG
Oxidation # -
represents the # of electrons that an atom gains or loses e.g. Na needs to lose 1 electron
to become stable thus 1+ ; whereas O needs
electrons thus
.
Rules : Oxidation numbers
1.
The oxidation # for any uncombined element is
is
and S in S8 is _____________
e.g. H in H2 is
and Zn in zinc metal
2.
The oxidation # of an element in an ionic compound is the charge on that ion e.g. in Li 2O ; since Li
is in group
it's charge is
and O is in group
its charge is ______________
Li2O ---> 2 x (+1) + -2 = 0
CaCl2 ---->
+2x(
)=0
3.
The oxidation # of Fluorine in compounds is always ___________________
4.
The oxidation # of oxygen in compounds is
a.
when combined with F e.g. OF2 ----> (
b.
in peroxides such as H2O2 ---> 2 x (
except :
) + 2 x (-1) = 0
)+2x(
)=0
5.
The oxidation # of hydrogen in compounds is
(+1) + ( ) =0
and CaH2 -------> ( ) + 2 x ( ) = 0
6.
The oxidation # of any other element in a molecule is selected so that the sum of the oxidation #'s
equal
in a molecule or the overall charge of the radical
e.g.
CO2 ----->
+2x(
HClO2 ----> +1 +
)=0
+ 2 x (-2) = 0
PO4-3 ---->
+ 4 x (-2) = -3
BF4- ----->
+ 4 x (-1) = -1
, except in metal hydrides such as NaH ---->
2
Balancing simple redox reactions :
Consider the reaction :
Mg(s) +
a.
b.
c.
d.
e.
O2(g) ------>
MgO(s)
Place oxidation #'s over each element
Balance the equation
Label the oxidation reaction ; involves a
of electrons and a
in oxid. #; and label
the reduction reaction the one that involves a
of electrons and a(an) _________ oxid. #
Label the oxidizing agent the one that is reduced and the reducing agent the one that is oxidized.
is the reducing agent ; each atom lost
e's for a total of
e’s and
is
the oxidizing agent; each atom gained
e's for a total of ________ e’s
Consider the following reactions and complete the table that follows
1.
Cl2
+ 2 Br-1 -----> 2Cl-1 + Br2
2.
Zn
+ 2 H+ -----> Zn+2
+ H2
3.
H2
+ Cl2 ------> 2 H+
+ 2 Cl-
4.
Cu + 4 HNO3 ------> Cu2+ + 2 NO3- + 2 H2O + 2 NO2
5.
2 Na + 2 H2O -----> 2 Na+ + 2 OH- + H2
6.
Cu + 2 Ag+ -----> Cu2+ + 2 Ag
7.
Br2 + 2 I- -----> I2 + 2 Br-
8.
2 MnO2 + 3I2 + 4 H2O ----> 6I- + 2 MnO4- + 8 H+
#
subst.oxid
subst.red.
1
2
3
4
5
6
7
8
Complete pg 653(2) pg 659(12,13,15) pg 662(18)
oxidizing
agent
reducing
agent
3
Assignment : Oxidation #'s and Redox equations
1.
State the Oxidation Number of each of the elements that is underlined.
a) NH3
_____
b) H2SO4
_____
c) ZnSO3
_____
d) Al(OH)3
_____
e) Na
_____
f) Cl2
_____
ClO4-
g) AgNO3
_____
h)
i) SO2
_____
j) K2Cr2O4
_____
k) Ca(ClO3)2
_____
l) K2Cr2O7
_____
m) HPO32-
_____
n) HClO
_____
o) MnO2
_____
p) KClO3
_____
q) PbO2
_____
r) PbSO4
_____
s) K2SO4
_____
t)
u) Na2O2
_____
v) FeO
NH4+
_____
_____
w) Fe2O3
_____
x)
y) NaIO3
_____
z) ClO3-
NO3-
aa)
_____
cc) S4O6
_____
_____
bb)
SiO44Cr(OH)4-
2.
State the oxidizing and reducing agent in each of the following :
a.
3 Cu+2 + 2 Al --------> 3 Cu
b.
NH4+
c.
2 NiO2H + Cd + 2 H2O ------> 2 Ni(OH)2 + Cd(OH)2
d.
C2O4-2 + MnO2 + 4 H+ ------> Mn2+ + 2 CO2 + 2 H2O
e.
I2O5 + 5 CO ------> 5 CO2 + I2
f.
Na2SO4 + 4 C -----> Na2S
g.
4 NaOH + Ca(OH)2 + C + 4 ClO2 ----> 4 NaClO2 + CaCO3 + 3 H2O
+ 2 Al3+
+ NO3- ---------> N2O + 2 H2O
+ 4 CO
_____
_____
_____
4
Day 2
Balancing Equations :
C3H8O + CrO3 + H2SO4 
Cr2(SO4)3 + C3H6O + H2O
1.
Oxidation # method (pg 664)
a.
b.
c.
d.
Balance all atoms except O and H
Write the oxidation #'s over each atom in the equation
Show the change in oxidation #
adjust the coefficients in the equation so that the total increase in oxidation # equals the total decrease in
oxidation #
Balance O by adding H2O
Balance the charge by adding H+ if in an acid solution. If in basic solution balance it as you would in acidic
but at the end add OH- to neutralize the H+. You must add the same amount of OH- to each side but note
on the one side it neutralizes to form water.
Make a final check on charge L.S. = R.S.
e.
f.
g.
5
Example 1
+7
MnO4a.
+4
+2
+6
+ H2SO3 -----> Mn+2 + HSO4-1 + H2O ( acidic )
All atoms other than O and H are balanced
i.
Mn+7 -----> Mn+2 ------> change -5 e's
ii.
S+4 -----> S+6 --------> change + 2 e's
d.
Multiply equation i by 2 and equation ii by 5
e.
2 MnO4- + 5 H2SO3 + H+
g.
L.S. = - 1 = R.S.
-----> 2 Mn+2 + 5 HSO4-1 + 3 H2O
Example 2 :
0
Zn
+3
+2
-3
+ As2O3 ------> Zn+2 + AsH3 ( basic )
a.
Put a
b.
i.
Zn ----> Zn2+ ------> change
ii.
+3
-3
As2 -----> 2 As -----> change
c.
d.
in front of AsH3
e's
e's
Multiply equation 1 by
Zn +
As2O3 +
H+
----->
Zn2+ +
AsH3 +
H2O
e.
Since it is in a basic solution add OH- to both sides so as to neutralize the H+
f.
6 Zn + As2O3 + 12 H+ +
6 Zn + As2O3 +
6 Zn + As2O3 +
----> 6 Zn2+ + 2 AsH3 + 3 H2O + __________
H2O -----> 6 Zn2+ + 2 AsH3 + 3 H2O + 12 OHH2O -----> 6 Zn2+ + 2 AsH3 + 12 OH-
6
Balance the following :
1.
I2 + HClO -------> IO3- + Cl- ( acidic )
2.
S-2
3.
CN- + IO3-
4.
ClO2
5.
HPO3-
6.
Ni(OH)2 +
+
ClO3-
------------>
------------->
SbO2- ---------->
+
+
BrO
-
Cl- + S
I-
BrO- --------> Br
+ CNO- ( base )
ClO2- +
--------> Br
-
( acid )
-
+
+
Sb(OH)6- ( base )
PO4-3
NiO2
( acid )
( base )
7
Balance each redox equation
a)
Co(OH)2 + H2O2 --------> Co(OH)3 + H2O
b)
HS2O4-
c)
PH3
d)
H2PO2- + CNO- ------------> CN-
e)
V +
f)
H2PO2-
+ AsO4-3 ---------> AsO2- +
+
CrO4-2
H2O
+
----------> Cr(OH)4-
--------> H2 + HV5O17 -2
TeO42- --------> PO43-
SO4-2
+
HPO3-
+
( acid )
( base )
P
( acid )
( base )
( base )
+
Te ( acidic )
8
Complete pg 668(2,3)
9
Review the oxidation number method for balancing redox reactions and practise using this
method.
1. NaI + HClO NaIO3 + HCl
2. I2 + HNO3 HIO3 + NO2 + H2O
3. C3H8O + CrO3 + H2SO4 Cr2(SO4)3 + C3H6O + H2O
5. Cu + H2SO4 CuSO4 + H2O + SO2
10
Day 3 2.
a.
b.
c.
d.
e.
f.
g.
h.
Half - Cell Method
Divide the skeleton equation into half cells
Balance all atoms other than O and H
Balance O by adding water
Balance hydrogen by adding H+
Balance the charge by adding electrons to the appropiate side
Make the e's lost by one half cell equal the e's gained by the other by multiplying by the appropiate #.
If basic media add OH- to both sides neutralizing the H+
Now add the 2 half cells and cancel where needed.
Example 1 : H2PO2-1 + CNO-1 ------> CN-1 + HPO3-1 ( acidic )
H2PO2-1 +
CNO- +
-----> HPO3-1 +
H2O
H+ +
e ------> CN-1 +
Multiply equation 1 by
H+ +
e
H2O
and equation 2 by
and add.
Net reaction is :
Example 2 : Sn(OH)42- + ClO3- + H2O ---> Sn(OH)62- + Cl-(basic)
Sn(OH)42-
ClO3-
-----> Sn(OH)62-
-----> Cl-
Example 3 : K2Cr2O7 + KBr + H2SO4 ---> K2SO4 + Cr2(SO4)3 + Br2 + H2O
K2Cr2O7 + H2SO4 +
KBr + H2SO4 +
+
---> K2SO4 + Cr2(SO4)3 + _____________
---> K2SO4 + Br2 +
___
+
_____
11
Assignment:
Balance the following (Half - Cell Method)
1.
Cu + NO3-1 ---> Cu2+ + NO ( acidic )
2.
S2- + ClO3- -----> Cl-1 + S ( basic )
3.
FeS + NO3- -----> NO + SO42- + Fe3+ ( acidic )
4.
H2O2 + Cr(OH)4- ------> CrO42- + H2O ( basic )
5.
KMnO4 + H2S + H2SO4 -----> K2SO4 + MnSO4 + H2O + S
12
6.
CuF2 + NH3 ------> Cu3N + NH4F + N2
7.
Tl2SO4 + K3Fe(CN)6 + KOH ---> Tl2O3 + K4Fe(CN)6 + K2SO4 + H2O
8.
Fe(CrO2)2 + Na2O2 -----> Na2CrO4 + Fe2O3 + Na2O
9.
Ca3(PO4)2 + SiO2 + C ---> P4 + CaSiO3 + CO
10.
NH4SCN + MnO4- ---> Mn2+ + N2 + CO2 + SO42- ( acidic )
13
Complete pg 673(3,4)
14
Review and practise the half-reaction method of balancing redox equations.
1. Balance the following equations, assuming acidic conditions.
(a) Br– + MnO4– Mn2+ + Br2
(b) HBiO3 + Mn2+ MnO4– + Bi3+
2. Balance the following equations, assuming basic conditions.
(a) S2– + ClO3– Cl– + S
(b) Sn(OH)42– + MnO4–MnO2 + Sn(OH)62–
15
Day 4 Electrochemical Cells(pg 695)
-
two common names are __________________________ and _____________________________
conversion of
____
energy into
______________
energy
Definitions :
Electrolyte -
a substance which in aqueous solution produces ions thus able to conduct electricity
Anion -
charged ion e.g.
Cation -
charged ion e.g.
Anode -
electrode at which
occurs and has a
Cathode -
electrode at which
occurs and has
MEMORY AID : RED CAT
charge
charge
AN OX
Salt Bridge -
tube that contains an electrolyte, that connects the 2 half cells of an electrochemical cell ( galvanic cell )
Voltmeter -
connects the 2 half cells via an electrical wire ; measures the potential difference between the 2 cells
Consider the electrochemical cell below that consists of the following:
silver metal, copper metal, silver nitrate solution, copper nitrate solution, salt bridge, voltmeter.
The following shorthand notation is often used :Cu(s)/Cu2+(aq)//Ag+(aq)/Ag(s)
The first one is the anode and the second is the cathode
16
1.
loses electrons, which build up on the
giving it a
to the
charge.(aNode)
2.
The excess electrons flow from the
3.
The oxidation of
increases the [
] around the anode. Due to repulsions, these ions begin to
drift away from the anode and migrate toward the cathode through the
;
Cations always travel toward the
.
4.
As Ag+ is
5.
At the anode : as oxidation occurs , net positive charge
from the
and negative ions move toward the
6.
At the Cathode : as reduction occurs, net positive charge
the cathode and negative ions move
.
to Ag(s) at the cathode; [Ag+]
along the external circuit.(fat cat)
around the cathode.
around the anode; positive ions move away
.
around the cathode; positive ions move
Net Reaction : _____________________________________________________________
Half Cell Potentials Standard Reduction Potentials (701) See chart pg 804

Convenient tabulation of electrochemical data.

Standard reduction potentials, Eored measured relative to the standard hydrogen electrode (SHE).

SHE: 2H+(aq, 1M) + 2e- --> H2(g, 1 atm), we assign Eored = 0.
Eocell = Eored(cathode) - Eored(anode)

Standard reduction potentials must be written as reduction reactions:
Zn2+(aq) + 2e- --> Zn(s), Eored = -0.76 V.

Eored = -0.76 V we conclude that the reduction of Zn2+ in the presence of the SHE is not spontaneous.

The oxidation of Zn with the SHE is spontaneous.

Changing the stoichiometric coefficient does not affect Eored.

Voltaic cells (spontaneous) Eored(cathode) is more positive than Eored(anode).
Zn + 2 H+ ----> Zn2+ + H2
-
Eocell = + 0.76 V
a positive Eocell indicates a spontaneous reaction in the direction written and a neg. value is non spontaneous
refer to the table of standard reduction potentials : the best oxidizing agent is F 2 ------> Eo = 2.87 V and
the poorest oxidizing agent is Li+ -----> Eo = -3.03 V ; the best reducing agent is
at a value of
; and the poorest reducing agent is
at a value of
.
17
Use the chart below as a quick reference for standard reduction potentials.
Standard Reduction Potentials
Non-Standard Reduction Portentials
18
Consider the reaction : Pb + Zn+2  Pb+2 + Zn
Eocell = _______________________________ = _____________________________
reaction is
a written but the reverse reaction would be _________________
Try These :
1.
2.
2 Au+3 + 6 I-
 3 I2
Fe2+ + 2 NO2 + 2 H2O 
+ 2 Cr+3
 2 Cr
+ 2 Au
Fe + 2 NO3- + 4 H+
+ 3 Ca2+
3.
3 Ca
4.
2 NO3- + 4 H+ + Fe+2  Fe+3 + 2 NO2 + 2 H2O
5.
5 Fe+2 + MnO4- + 8 H+  5 Fe+3 + Mn+2 + 4 H2O
6.
Would it be possible to store a CuSO4 solution in an Aluminum container ?
CuSO4 ----->
____ + ______
Al +
Eocell =
----->
+ ________________
= ____________________ Statement :
7.
Copper metal can be obtained from scrap iron by allowing a solution containing Cu2+ ions to trickle over the scrap.
Assuming the iron metal changes to Fe2+ ; write the net reaction and calculate the voltage produced.
8.
Explain using equations and Eo's what would happen if an aluminum spoon was used to stir an Fe(NO3)2 solution.
19
9.
Given : ( Z, Y, X, T are hypothetical )
T + Y+2
Z + Y2+
X + T2+
-----> T2+
-----> N.R.
-----> X2+
+ Y
+ T
Arrange the above hypothetical elements into a short redox series putting at the top the half-reaction ( oxidation )
which has the greatest tendency to lose electrons.
10.
Label completely(cathode, anode, positive electrode, negative electrode and show direction of electron and ion
flow and answer the questions that follow.
a.
In which cell does reduction occur ?
_____________________
b.
Write the half cell reactions involved :
_____________________
c.
Which metal is the anode ?
d.
Which ions travel to the anode ?
e.
What ions travel to the cathode ?
f.
What is the net reaction and what is the voltage produced ?
________
_______
______________________
20
Describe each reaction as spontaneous or non-spontaneous.
1. Au+3
Fe+3
----->
Fe+3
------>
Fe+2
F2
+
Fe+2
2. Pb
+
3. Cl2
+
F-
------>
4.Cu+2
+
2Br-
------>
Cu
+
Au
+
+
+
Pb+2
2Cl-
Br2
6. Sn+2
+
Br2
------>
Sn+4
+
2Br-
7. Pb+2
+
Fe+2
------>
Fe+3
+
Pb
8.
Can you keep 1 mol/L HCl in an iron container. If the answer is no, write a balanced equation for the reaction
that would occur.
9.
Can you keep 1 mol/L HCl in an Ag container. If the answer is no, write a balanced equation for the reaction
that would occur.
10.
Can you keep 1 mol/L HNO3 in an Ag container. If the answer is no, write a balanced equation for the reaction
that would occur. (remember HNO3 consists of two ions H+ and NO3-)
11.
Can you keep 1 mol/L HNO3 in an Au container. If the answer is no, write a balanced equation for the reaction
that would occur. (Remember, HNO3 consists of two ions H+ and NO3-)
21
Complete pg 700(6,8) pg 708(10,11) pg 709(7,8)
Day 5 Lab Electrochemical cells ( pg 721 )
Day 6 Applications (pg 688):
Batteries 1.
group of galvanic cells connected in series so that the total voltage is the sum of the
individual cells.
Lead Storage Battery (pg 689)
-
classified as a _________________ cell since it can be recharged
anode is made of ____________ and has a ______________ charge ; the cathode is lead coated with
_______________ and has a _____________ charge ; electrolytic solution is
__________
acid
Anode :
Pb + HSO4- -----> PbSO4 + H+ + 2e
Cathode :
PbO2 + HSO4- + 3 H+ + 2e ----> PbSO4 + 2 H2O
Net Reaction is : ________________________________________
-
car batteries have
cells ; each producing
volts for a total of
Why can these cells be recharged ? ______________________________________
volts.
22
2.
Dry Cell (pg 688)
-
a.
classified as a _________________ cell since they cannot be recharged
Acid version - anode is a zinc inner case and the cathode is a carbon rod in contact with a moist paste of
manganese dioxide, and ammonium chloride
Zn ----> Zn2+
Anode :
+ 2e
2 NH4+ + 2 MnO2 + 2e ----> Mn2O3 + 2 NH3 + H2O
-------------------------------------------------------net reaction :
Cathode :
b.
cell produces a voltage of about
Alkaline version -
volts
ammonium chloride is replaced with KOH or NaOH
Anode :
Zn + 2 OH- ---> ZnO + H2O + 2e
Cathode :
2 MnO2 + H2O + 2e ----> Mn2O3 + 2 OH----------------------------------------------------------
net reaction :
lasts longer since zinc corrodes less rapidly under alkaline conditions; higher currents for longer period of
time
c.
Nickel - Cadium Re-Chargeable Battery
Anode :
classified as a ________________________ cell
Cd + 2 OH- ------> Cd(OH)2 + 2e
Cathode :
NiO2 + 2 H2O + 2e -----> Ni(OH)2 + 2 OH----------------------------------------------------------Net reaction :
d.
voltage produced by each cell is ______________Volts
rechargeable since _____________________________________________________
Fuel cells (pg 691)
-
oxygen gas is pumped in at the ___________________ and hydrogen at the _______________
-
electrolyte is _______________________________
23
Advantages ;
1.
_______________________________________________________________________
2.
______________________________________________________________________
Ballard Fuel Cell (pg691)
-
uses a ______________ _________________ membrane instead of a n ________
-
What separates the anode and cathode from one another ? _________________
Anode reaction :
Cathode reaction :
What are some problems with these cells ?
Complete pg 693 (17) pg 694(5,8,9)
24
Independent Research : Fuel Cells
-
assess, on the basis of research, the viability of using electrochemical technologies as alternatives as
alternative sources of energy, e.g fuel cells for emergency generation or as power sources in remote
locations), and explain their potential impact on society and the environment. Consider the following issue :
Hydrogen fuel cells use hydrogen as the fuel and oxygen as the oxidant, and produce water, rather than
environmentally harmful greenhouse gases, as waste. Although some cars run on such cells, practical
problems must be resolved before this source of energy is commonly used in the transportation sector.
Questions to consider :
1.
What is the capacity of a standard rechargeable battery before it has to be recharged ?
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
2.
What methods should be used to dispose of depleted batteries ?
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
3.
What impact has the use of rechargeable batteries in portable electronic devices had on society ( watch
video how stuff works – type in rechargeable batteries)?
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
25
Fuel Cells www.teachersdomain.org
Although carbon dioxide (CO2) is a naturally occurring and non-toxic gas, human activities have increased its
concentration in the atmosphere far beyond natural levels. CO2 is a greenhouse gas. It allows solar radiation to pass
through the atmosphere and be absorbed by Earth's surface but prevents the energy that is reradiated from escaping
back into space. The burning of fossil fuels, which releases the energy we use to power our cars and many other
things is widely believed to be the primary culprit behind the recent CO 2 buildup.
Hydrogen is a potential alternative source of energy for vehicles, portable electronics, and even home power
generators. Hydrogen can be used as an energy source for fuel cells, which, like gasoline engines and household
batteries, are a type of energy conversion device. However, unlike engines and batteries, fuel cells don't produce
harmful emissions, and they don't "go dead." With a fuel cell, as long as there is a flow of the chemical elements
hydrogen and oxygen into the cell, electricity will flow out of the cell.
Fuel cells designed to run on hydrogen combine hydrogen with free oxygen in the air and produce water. Electricity is
released during the reaction. Because hydrogen fuel cells produce energy with no harm to the environment water and
heat are the only by products it has been touted as a replacement for the internal combustion engine.
Although hydrogen is abundant on Earth, it is combined with other molecules in some other form such as with oxygen
as water. Because a fuel cell requires pure hydrogen, the great technological challenge is to separate hydrogen from
other molecules for use. Even though scientists and engineers have proven they can remove hydrogen from water, the
separation process requires a great deal of energy that must be provided by another fuel source. Using natural gas or
coal for this purpose would, of course, produce more CO2 emissions precisely what fuel cells are designed to lessen.
Non-polluting, renewable sources of energy, including solar cells, wind turbines, or hydroelectric dams, might one day
fuel the hydrogen extraction process. But such a solution has not yet proven to be efficient — more energy is spent
than is generated. In 2004, Iceland opened its first commercial hydrogen filling station. Iceland already derives 90
percent of its electricity from turbines driven by steam from renewable hot water springs that originate deep
underground. Iceland's government has committed to powering its cars and fishing fleet with cleanly produced
hydrogen within the next 25 years.
26
Fuel Cell Worksheet Name ________________________________________________________
1. Explain how a fuel cell works.
2. Compare the gasoline engine now common in cars with fuel cells. What are the advantages and disadvantages
of each?
3. Do you think that researching how to obtain a pure source of hydrogen for fuel cells is a good investment?
Why or why not?
4. Do research to find out and compare the amount of CO2 given off by vehicles and by power plants.
5. Should we be trying to use fuel cells in cars and other vehicles, or is there another more important way that
we should be using fuel cells to reduce the burning of hydrocarbons? Explain your answer.
27
Global Warming The Hydrogen Car : www.teachersdomain.org
Fossil fuels, including coal, petroleum, and natural gas, contain stored energy from organic compounds that
originated millions of years ago in living plants and animals. To access this energy, we burn these fuels, and as we
do, air pollutants and certain harmful gases are released into the atmosphere. Among these emissions is carbon
dioxide (CO2). Although CO2 is a naturally occurring and nontoxic gas, human activities have increased its
concentration in the atmosphere well beyond natural levels. Most climatologists link heightened levels of
atmospheric CO2 to accelerated global warming. This is because CO2 (along with methane, nitrous oxide, and
water vapor) is a known greenhouse gas, and greenhouse gases act much like the glass of a greenhouse:
Allowing
sunlight
in
but
preventing
heat
from
escaping.
Another possible source of energy for cars -- one that gives off non-toxic by-products -- is hydrogen. Because its
by-products don't harm the environment, the hydrogen fuel cell, which produces electricity capable of powering
cars and other vehicles, has been touted by many as a promising replacement for the internal combustion engine.
Fuel cell technology is proven but nevertheless problematic. Like batteries, fuel cells turn chemical energy into
electricity. A fuel cell, using a platinum catalyst, combines hydrogen and oxygen into water in a way that produces
an electric potential, like that of a battery. In vehicles, the electric current is routed to small motors in the wheels,
and the by-products -- heat and water -- are released into the air through a tailpipe.
Unlike fossil fuel resources, which are extracted from the ground, hydrogen must be made. Hydrogen can be
removed from water using another fuel, such as natural gas or coal, to power the extraction process, but this
creates CO2. Thus, the challenge is to find a way to extract hydrogen using a carbon-free energy source. Nonpolluting, renewable sources of energy, like solar cells, wind turbines, or hydroelectric dams, might one day fuel
the extraction process, but at present such a solution would not be efficient. The other problem with hydrogen as a
fuel is that a distribution and refueling infrastructure to serve drivers of hydrogen-powered cars would be
extremely expensive.
Questions
1. Approximately what fraction of carbon-dioxide emissions in the United States and in Canada comes from
automobiles?
2. How is a hydrogen fuel cell different from an internal combustion engine? What is its waste product?
3. What are the pros and cons of a hydrogen car?
4. Do you think the hydrogen car is the answer to global warming?
5. What are some possible non-carbon sources of hydrogen?
28
Day 7 Corrosion Of Iron (pg 710)
-
steel has a nonuniform surface thus composition is not completely homogeneous and physical strains leave stress
points in the metal thus in these areas the iron is more easily oxidized ( anode ) than at others ( cathodic areas )
Anode : Fe ------> Fe2+
+
2e
travels to the
Cathode :
O2 + 2 H2O + 4e -----> 4 OH-
-
the cation
( Fe2O3 . nH2O (s) ))
and reacts with oxygen to form rust
-
moisture must be present to act as a salt bridge between the anode and cathode ; salting roads also accelerates
the rusting process. See Mr Doyles first car below :
Prevention Of Rusting
1.
Painting -
protects the metal from oxygen and moisture
2.
Galvanizing -
zinc is used to coat the steel but since Zn is more reactive it is the Zn that oxidizes not the Fe ;
Zinc acts as the Sacrificial Anode
3.
Cathodic Protection -
used to protect steel in buried fuel tanks and pipelines; an active metal such as
Magnesium is connected to the pipeline by a wire thus Mg oxidizes not the iron; also
found on hulls of ships.
4.
Impressed Current -
alternate method involves connecting a battery such that the negative terminal is
connected to the ________________________ and the positive terminal is connected
to _________________
29
Complete page 714(2,3,7,10) Complete page 725(1-18) Pg 726(4,6,8,9,10,13,15,16,20,21,22,24)
30
Independent Research
-
Analyse health and safety issues involving electrochemistry ( e.g corrosion of metal pipes in drinking water
systems. Consider the following ; corrosion is a leading cause of structural degradation of bridges and
roadways. Not only does rust weaken metal structures, but as it builds up it forces apart connecting parts
of the structure, causing the structure to fail and risking public safety. Yet methods used to prevent
corrosion may also have a negative effects on human health. Consider the following questions ;
1.
What health and safety hazards are associated with waste generated by electroplating companies ( watch
video how stuff works – type in electroplating wastes).
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
2.
Why do metal orthodontic braces not corrode.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
3.
What are some of the toxic substances that can escape from electronic waste into the environment.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
4.
What are the potential effects of these poisons on our health.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
31
-
Students research and assess environmental, health, and safety issues involving electrochemistry, e.g., the
corrosion of metal structures by oxidizing agents, industrial production of chlorine by electrolysis and its
use in the purification of water, the use of antioxidants BHT (butylated hydroxytoluene) and BHA
(butylhydroxyanisole) as food additives.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
Day 8 Electrolysis(pg 730)
-
uses electrical energy to produce a chemical change
Ex. 1
Electrolysis of Molten NaCl using platinum electrodes
Anode
(oxidation)
e
+
Cathode
(reduction)
e
-
-
-
+
Na+
Cl
-
Cathode : 2 Na+
+ 1e ------> 2 Na (l)
Anode : 2 Cl- ------> Cl2 + 2 e
-------------------------------------------------------------------Net reaction :
_______________
Minimum voltage needed to run this cell is
Eo = - 2.71 V
Eo = - 1.36 V
Eocell = ___________
32
Ex. 2
Electrolysis of Water using Pt electrodes :
Cathode :
2 H2O + 2e -------> H2 + 2 OH-
Eo = __________
Anode :
H2O
---------> 1/2 O2 + 2 H+ + 2 e
Eo = __________
-----------------------------------------------------------------------------------------Net reaction :
Eocell = _____________
Ex. 3
Electrolysis of NiI2 using Pt electrodes
Cathode :
or
Eo = ____________
Eo = ____________
Favoured reaction is ____________________________________
Anode :
or
Eo = ____________
Eo = ____________
Favoured reaction is _________________________________
Net Reaction is
Ex. 4
; min. voltage neeeded is ____________________
Electrolysis of 1.0 mol/L CuF2 with Pt electrodes
Cathode :
or
Eo=
Eo =
Anode :
or
Eo =
Eo =
Net Reaction is
; min. voltage needed is ________________
Try These :
1.
1.0 mol/L CoI2 and 1.0 mol/L HCl using Pt electrodes
2.
1.0 mol/L NaOH using Fe electrodes
3.
1.0 mol/L HI using Cu electrodes
4.
1.0 mol/L NiSO4 using Pt electrodes
5.
An aqueous solution of Na2SO4 is electrolyzed. If litmus paper was dipped around the anode and the
cathode what colours would you get and if the current was turned off and the two solutions stirred together
what is the final pH.
33
Complete pg 735 (1b,3,4) Pg 736(6,7)
Reading assignment pg 738-743(Make brief notes) Complete pg 741(1,4,) pg 744(8,9,11,14)
Pg. 746 (6,11)
34
Electrolysis: Electroplating
Qualitative:
The process of electroplating can be accomplished by placing the object to be plated at the __________
(reduction) and place the metal you want to plate with at the__________ (oxidation). The electrolyte
solution should have as its cation the same as the metal at the anode.
CATHODE
-
+
ANODE
Cu2+ + 2e1- → Cu
Cu → Cu2+ + 2e1Cu
metal object
CuSO4(aq)
Cu2+
CuSO4(aq)
At the ________, the Cu is stripped of two of its electrons which travel through the external wire. At the same
time a Cu2+ ion moves into solution. At the __________, the Cu2+ is attracted to the cathode and will plate on
the two electrons deposited there by the battery.
35
Aluminium Extraction By Electrolysis (pg 739)
Complete the following sentences about the extraction of aluminium by electrolysis:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
The name of aluminium ore is ________________________________
Aluminium ore is purified to extract a white powder. The chemical name for this material is _________
The chemical formula for this material is ________________
Electricity is used to extract aluminium, rather than a simple reduction reaction with carbon or carbon
monoxide. This is because __________________________
The melting point of aluminium oxide is ____________________
The melting point of cryolite is ___________________
Manufacturers use aluminium oxide dissolved in cryolite in their electrolysis cells. This is better than
melted aluminium oxide on its own because ____________________
The name is given to the positive electrode in an electrolysis cell is ______________________
The positive electrode is made out of ____________________________
The shape of the positive electrodes is ___________________________
The position of these electrodes in the electrolysis cell can be described as ______________
The ions which move towards the anode are called ______________________________
A word equation for the reaction which occurs at the anode is _______________________
A balanced symbol equation for this reaction is _____________________
The type of reaction occurring at the anode is called _______________________________
Oxygen gas is a product at the anode. A word equation for the reaction of this oxygen with the anode
material is _____________________________
The unwanted anode reaction causes a problem for aluminium manufacturers. The problem is ______
Aluminium manufacturers overcome their problem by ______________________________
The name given to the negative electrode in an electrolysis cell is _____________________________
The negative electrode is made out of ______________________________
The position of the negative electrode in the electrolysis cell can be described as __________________
The ions which move towards the cathode are called _____________________________
A word equation for the reaction which occurs at the cathode is ________________________________
A balanced symbol equation for this reaction is ______________________________________
The type of reaction occurring at the cathode is called _____________________________
There are three states of matter: solid, liquid and gas. When it first forms in the electrolysis cell the
aluminium is a ___________________________
In the electrolysis cell, newly formed aluminium collects __________________________
Complete pg 759(1-4,8-12,14,16)pg 760(2,4,5,7)
Unit review pg 764(1-36, omit 13,15,31,32) 768(3,5,7,9,12,16,18,24,26,34)
36
Sch4u1 Unit 5 review
Modified True/False
Indicate whether the sentence or statement is true or false. If false, change the identified word or phrase to make the
sentence or statement true.
____
1. Oxidation processes always result in a decrease in the oxidation number of a species.
_________________________
____
2.
____
3. Silver is a stronger reducing agent than aluminum. _________________________
____
4. Reduction processes always result in a decrease in the oxidation number of a species.
_________________________
____
5. When an atom loses an electron in a redox reaction, it is acting as an oxidizing agent.
____
6. In a redox table, the strongest oxidizing agent is at the top left side of the table. _________________________
is a better oxidizing agent than
. _________________________
_________________________
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
____
7. In the reaction
+
+
+
+
Which of the following statements is correct?
a.
is the reducing agent, and
is the oxidizing agent
b.
c.
____
is the reducing agent, and
d.
is the reducing agent, and
is the reducing agent, and
is the oxidizing agent
is the oxidizing agent
e.
is the reducing agent, and
is the oxidizing agent
8. The oxidation number of chromium (
a. +2
b. +4
c. +6
____
is the oxidizing agent
) in the dichromate ion (
d. +7
e.
9. The oxidation number of nitrogen ,
a. +1
b. +2
c. +3
, in the nitrite ion,
d.
e.
, is
3
1
____ 10. In the reaction
+
+
+
Which of the following statements is correct?
a. hydrogen is oxidized and
is the oxidizing agent
b. hydrogen is oxidized and
is the oxidizing agent
c.
carbon is oxidized and
is the oxidizing agent
d. manganese is oxidized and
is the oxidizing agent
e. carbon is oxidized and
is the oxidizing agent
+
) is
37
____ 11. Consider the following unbalanced redox reaction:
+
+
+
+
The coefficients in the balanced equation are, from left to right
a. 1, 1, 6, 1, 1, 3
d. 1, 6, 6, 1, 6, 3
b. 1, 2, 6, 1, 2, 3
e. 2, 1, 12, 2, 1, 6
c. 2, 3, 12, 2, 3, 6
____ 12. Experiments were performed with four strips of metals , , , and , and their corresponding nitrate solutions
,
,
, and
. The following observations were obtained:
A
no reaction
no reaction
no reaction
no reaction
precipitate
no reaction
precipitate
precipitate
precipitate
no reaction
no reaction
no reaction
precipitate
no reaction
precipitate
no reaction
Which of the following is the correct list of the metal ions in order of decreasing strength as oxidizing agents
(strongest oxidizing agent first)?
a.
d.
b.
e.
c.
____ 13. Which element is oxidized in the following reaction?
a.
in
d.
b.
in
e.
c.
in
in
____ 14. The following two half-reactions are involved in a galvanic cell:
At standard conditions, what species are produced at each electrode?
a.
is produced at the cathode and
at the anode
b.
is produced at the cathode and
at the anode
c.
is produced at the anode and
at the cathode
d.
is produced at the cathode and
at the anode
e.
is produced at the cathode and
at the anode
____ 15. An electrochemical cell is set up with a copper electrode in contact with 1.0 mol/L
electrode in contact with 1.0 mol/L
. The standard reduction potentials are
C, the standard cell potential for this galvanic cell in volts is
a. 0.13
b. 0.34
c. 0.47
d. 0.21
e. 0.94
and a lead
38
____ 16. In the electrochemical cell above, the left half cell is set up with a zinc electrode in contact with 1.0 mol/L
and the right half-cell is set up with a silver electrode in contact with 1.0 mol/L
.
The relevant reduction potentials are
Which of the following statements is false?
a. the silver electrode is the cathode
b. increasing the
will increase the cell voltage
c. electrons in the external circuit will flow from zinc to silver
d. the standard cell potential for this cell is 1.56 V
e. the zinc electrode is the anode
____ 17. Consider the abov
C.
In the left half-cell, a lead electrode is in contact with 0.10 mol/L
copper electrode is in contact with 0.20 mol/L
and in the right half-cell, a
. The standard reduction potentials are as follows:
Which of the following statements about this cell is false?
a.
ions migrate into the left half-cell through the salt bridge
b. electrons flow from the copper electrode to the lead electrode
c. the cell is not at standard conditions
d.
ions migrate into the right half-cell through the salt bridge
e. reduction occurs at the copper electrode
18. Calculate
for the following equation:
Decide whether the equation represents a spontaneous or a nonspontaneous reaction at standard conditions.
39
19. Balance the following equation by the half-reaction method:
+
+
+
20. Balance the following equation and identify the oxidizing and reducing agents:
21. The following unbalanced net ionic equation represents the reaction in which ethanol,
acidified potassium permanganate solution to ethanoic acid,
Use the half-reaction method to balance the above equation.
:
, is oxidized by
40