Transcript Slide 1

How can we construct different types of
electrochemical cells and how are the
properties and applications of these cells
different?
Dr. Robert H. Winston
Northeastern RET 2010
Thomas A. Edison CTE High School
& HALB DRS High School
1
National Science Education Content Standards (Grades 9-12)
A—Science as Inquiry: Abilities necessary to do scientific inquiry
1) Results of scientific inquiry--new knowledge and methods--emerge
from different types of investigations and public communication
among scientists.
2) In communicating and defending the results of scientific inquiry,
arguments must be logical and demonstrate connections between
natural phenomena, investigations, and the historical body of
scientific knowledge.
3) In addition, the methods and procedures that scientists used to
obtain evidence must be clearly reported to enhance opportunities
for further investigation.
B—Fundamental concepts and principles that underlie the conservation of
energy and in disorder
E—Fundamental abilities and concepts used to identify a problem; propose
a design and choose between alternative solutions; implement a proposed
solution; and evaluate the solution and its consequences
G—History and Nature of Science—Nature of scientific knowledge.
Scientific explanations must meet certain criteria.
2
NY State Standards:
1. Students will use mathematical analysis, scientific inquiry, and
engineering design, as appropriate, to pose questions, seek answers,
and develop solutions.
• S1.1 Elaborate on basic scientific and personal explanations of
natural phenomena, and develop extended visual models and
mathematical formulations to represent their thinking
• S1.2 The observations made while testing proposed
explanations, when analyzed using conventional and invented
methods, provide new insights into natural phenomena.
• E1.1 Initiate and carry out a thorough investigation of an
unfamiliar situation and identify needs and opportunities for
technological invention or innovation
2. Students will access, generate, process, and transfer information
using appropriate technologies.
4. Students will understand and apply scientific concepts, principles,
and theories pertaining to the physical setting and recognize the
historical development of ideas in science.
7. Students will apply the knowledge and thinking skills of science
and technology to address real-life problems and make informed
decisions.
3
Instructional Objectives
Students will be able to:
1. Describe a way to obtain electrical energy from an oxidation reduction
(redox) reaction
2. Identify the parts of a voltaic cells and explain how each part operates
3. Calculate cell potentials and determine the spontaneity of redox
reactions
4. Identify the parts of an electrolytic cell and explain how each part
operates
5. Describe how electrolytic cells are different from voltaic cells
6. Explain some practical application of both voltaic and electrolytic cells
7. Explain how fuel cells work
8. Describe what conditions predispose towards the corrosion of metals
4
Anticipatory Set
• Discuss/review concepts of electrical charges, ion formation, chemical
equilibrium and oxidation reactions
Motivation
Say, “Please carefully watch and listen to me as I
take this lemon and insert two metallic strips: one
Cu and one Zn into it. I am going to the attach a
BLACK wire to the Zn strip and a RED wire to the
Cu strip. The other ends of these wires are
attached to a digital voltmeter. “
Ask, “What is happening with the meter?”
Challenge->Think Pair Share with your nearest
neighbor. Write down “ “How…” and “Why does all
of this happen?”
5
Definitions:
CATHODE
REDUCTION occurs at this electrode
ANODE
OXIDATION occurs at this electrode
But wait a moment,
“What are oxidation and reduction?
Challenge, “How do these redox reactions affect
the charge of each electrode?” “Why would an
6
electric current be produced?”
Development Part #1—Voltaic / Galvanic Cells
1. Demonstrate how Voltaic/Galvanic Cells work
2. Voltaic Cells use spontaneous oxidation-reduction
reactions to convert chemical energy into electrical
energy
3. Watch this animation carefully with your Think
Pair Share partner
Ask, “Why is there an electric
current generated?” And
then ask, “What is the purpose of
the salt bridge?”
7
4.
Let the students carry out the following simulation with their
laptops and the SmartBoard concomitantly.
Electrochemical Cells
Think Pair Share:
What variables appear to
affect the magnitude of
electricity produced in
Galvanic cells?
Based on your knowledge
of chemistry, how could
we calculate the amount
of voltage being generated?
Be sure to: Tabulate all your data, create useful graphs, and
answer all of the questions?
8
5. Describe the relationship between voltage and the
motion of electrons
For every electron, an atom of
silver is plated on the electrode.
eAg+ + e-  Ag0
Electrical current is expressed
in terms of the ampere, which
is defined as that strength of
current which, when passed
through a solution of AgNO3
(aq) under standard conditions,
will deposit silver at the rate of
0.001118 g Ag/sec
Ag+
Ag0
1 amp = 0.001118 g Ag/sec
9
Michael Faraday’s Law of Electrolysis
The mass deposited or eroded from an
electrode depends on the quantity of electricity.
Quantity of electricity – coulomb (Q)
Q is the product of current in
amps times time in seconds
coulomb
Q = It
time in seconds
current in amperes (amp)
1 coulomb = 1 amp-sec = 0.001118 g Ag
10
Faraday’s Law allowed us to determine the quantity of
material deposited!!
Ag+ + e-  Ag
1.00 mole e- = 1.00 mole Ag = 107.87 g Ag
107.87 g Ag/mole e0.001118 g Ag/coul
= 96,485 coul/mole e-
mole e- = Q/F
1 Faraday (F )
mass = molemetal x MM
molemetal depends on the half-cell reaction
11
Part 1 Activities (continued)
6. Homework
a. Write up a “Simulation Report”. Be sure to
answer all of the questions.
b. Be able answer some extended response
questions on the theory and practical
application behind
b. Galvanic (Voltaic) Cells
c. Electrolytic “
d. Fuel “
12
7. Closure Video
Watch and listen to this carefully!
Write out the answer to this: “When the Zn0 is oxidized, how does
the fact that the reaction proceeds faster if heated relate to the
spontaneity of the formation of the ZnO? How do this relate to the
ΔG and Δε of the overall reaction?
13
Part #2—Electrolytic Cells +
Pose the following question:
“How do compounds like acids, bases and salts change the
electrochemical properties of water when they’re added to
it?” Elicit students’ responses while directing a basketballtype discussion.
Follow-up with, “How does this explain why metal statues
near the ocean tend to rust much quicker than ones equally
close to the lakes and rivers?”
Motivation
Demonstrate electroplating of copper on to a zinc or iron
electrode. Challenge your students by asking, “Why isn’t
this a voltaic cell?” “How are these events different?”
Elicit, “That for one thing electricity is not produced.” Say,
“It’s an electrolytic process in which a cation is reduced
14
and a solid metal is deposited on a surface.”
Part #2—Lesson
1. You are going to break up into groups of four
(Work Share Quads) and you will carry out a real-time lab
experiment**:
Galvanic and Electrolytic Cells
Overview:
Part A: Determining the Voltage of Electro-chemical
Cells
Part B: Examination of Electrolytic cell using carbon
electrodes in a KI solution
Part C: Electroplating Pennies and calculating Faraday’s
Law
**-Each group will only do two of the parts-A,B and/or C. I’ll
come around and tell your parts. All groups will have to share
15
their data with the other groups!!
Part #2—Activities
2.Watch the next slide about the Hall Process
OK break up into your Work Share Quads as
before and be able to answer these questions:
(a) Is this electrolytic or galvanic?
Why?
(b) spontaneous or not spontaneous—
Why? Now ask, “How could you
prove it!
16
The Hall Process for …
e- 
+
graphite anodes
from
power
source
CO2
bubbles
Al+3
-
Al+3
 e-
O-2
O-2
O-2
Al2O3 (l)
Al (l)
carbon-lined steel vessel
acts as cathode
Draw
off
Al (l)
Cathode: Al+3 + 3e-  Alo (l)
Anode: 2O-2 + Co (s)  CO2 (g) + 4e-
17
Closure Activity 
Fuel Cells
Challenge, “How do fuel cells work? Are they more
comparable to Galvanic or electrolytic cells or are they in a
league all their own? Why? [Write out your answer!]
18
Homework:
a. Review all of the concepts
thoroughly!
b. Do the entire Lab Report
c. Students are to explain what
happens in the Hall Process.
d. Be sure to explain and account
for why the Al is deposited at
one electrode and not the other.
19
Extra Credit-Individual Efforts Only
• Challenge, “How are Electrolytic and Voltaic cells
different electrochemically and thermodynamically?”
•Describe what Cyclic Voltammetry and Chronoamperometry are!
20
Resources-Click diagrams for instantaneous
access!
1.
2.
3.
Periodic Table
of pH
Electrochemistry
Measurement
Standard Electrode Potentials in Aqueous
Solution at 25°C
21
Here’s what Dr. Robert does in laboratories in other places:
How peculiar doctor, the cells seem to be multiplying
randomly—come have a look for yourself!!!
22
Acknowledgements
•
Claire J. Duggan, Center for STEM Education & Program Director of
the RET @ Northeastern University
•
Rocco Cieri, Medford Public Schools
•
The RET Class of 2010
•
Professor Patricia Ann Mabrouk, Chemistry and Chemical Biology
Department@ Northeastern University
•
Chemistry and Chemical Biology Department @ Northeastern
University
23