General Chemistry II

Course Title: CHEM 1302: General Chemistry II

Lecture Topic: Electrochemistry: Galvanic/Voltaic Cells

Instructor: Dr. Smith

Institution: University of Texas - Pan American

Backwards Design

Course Objectives

• Primary Objectives- By the next class period students will be able to:
  • By the next class period students will be able to:
    • draw and label a simple galvanic/voltaic cell
    • explain the function of a salt bridge
    • write chemical equations for the chemical reactions occurring in each half-cell
    • write an overall chemical equation for the galvanic/voltaic cell
    • identify the anode and the cathode in the galvanic/voltaic cell

• Sub Objectives- The objectives will require that students be able to:
  • The objectives will require that students be able to:
    • understand the concepts of oxidation and reduction
    • understand the concept of electromotive force
    • understand how to balance chemical equations

• Difficulties- Students may have difficulty:
  • Students sometimes have difficulty distinguishing between oxidation and reduction reactions. Students also sometimes have difficulty balancing chemical reactions. Students also have misconceptions about the movement of particles (electrons, cations, anions) throughout the galvanic/voltaic cell.

• Real-World Contexts- There are many ways that students can use this material in the real-world, such as:
  • Batteries! Most people have used batteries of one sort of another, whether they are aware or not. Batteries are present in toys, cars, cell phones, watches, laptop computers, and a host of other everyday items. Students might be interested in learning about how batteries work, why batteries die, and how some batteries can be recharged.

Model of Knowledge

• Concept Map
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• Content Priorities
  • Enduring Understanding
    • Understand how to draw a label a simple galvanic/voltaic cell
    • Understand how the salt bridge functions to maintain electrical neutrality
    • Understand how to determine the chemical reactions occurring in each half-cell
    • Understand how to determine the overall chemical equation for the galvanic/voltaic cell
    • Understand how to identify the anode and cathode in the galvanic/voltaic cell
    • Understand how qualitative observations in the half-cells relate to the chemistry and function of each half-cell
    • Understand how to relate simple galvanic/voltaic cells to batteries

• • Important to Do and Know
    • Understand how to draw and label more complicated galvanic/voltaic cells
    • Understand how more complicated galvanic/voltaic cells function

• • Worth Being Familiar with
    • Familiarity with shorthand cell notation for galvanic/voltaic cells
    • Familiarity with the chemical reactions occurring in common types of batteries
    • Understand why some batteries die
    • Understand why some batteries can be recharged

Assessment of Learning

• Formative Assessment
  • In Class (groups)
    • Group questions: questions on galvanic/voltaic cells (see below)
      • A galvanic cell consists of a silver-silver ion half-cell and a nickel-nickel(II) ion half-cell; silver ion is reduced during operation of the cell.
        • a) What is the oxidation half-reaction?
        • b) What is the reduction half-reaction?
        • c) What is the overall cell reaction?
        • d) Which metal is the cathode?
        • e) Which metal is the anode?
      • Calculate E°cell for the following electrochemical cell:

2Al(s) + 3Fe2+(aq) ↔ 2Al3+(aq) + 3Fe(s)

• • Homework (individual)
    • Questions on galvanic/voltaic cells topics (see below)
• Summative Assessment
  • Exam questions

Legacy Cycle

OBJECTIVE

By the next class period, students will be able to:

• draw and label a simple galvanic/voltaic cell
• explain the function of a salt bridge
• write chemical equations for the chemical reactions occurring in each half-cell
• write an overall chemical equation for the galvanic/voltaic cell
• identify the anode and the cathode in the galvanic/voltaic cell

The objectives will require that students be able to:

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THE CHALLENGE

Everybody uses toys, cell phones, and gizmos that require batteries. Everybody knows that batteries eventually die. How do batteries work, and why do they die?

GENERATE IDEAS

Several guiding questions to help students generate questions: What are some of the different kinds of batteries that you have used and seen before? What comes from a battery that causes your toys or cell phones or gizmos to work? What do different batteries look like, in terms of size and shape? How do the costs of different batteries compare to one another?

MULTIPLE PERSPECTIVES

Let’s take a look at a lead storage battery. First we’ll look at a picture of it to see what it looks like: (Source: http://www.answers.com/topic/lead-acid-battery-1 accessed May 2009)

Next we’ll look at a schematic to see what the different parts are: (Source: http://library.tedankara.k12.tr/chemistry/vol4/Batteries/z175.htm accessed May, 2009) Next we’ll look at the chemical reactions occurring in the battery: Cathode: PbO2 (s) + 2e- + 4 H+ (aq ) + SO42- (aq ) --> PbSO4 (s) + 2 H2O (l ) Anode: Pb (s) + SO42- (aq ) --> PbSO4 (s) + 2e-

RESEARCH & REVISE

There are lots of different kinds of batteries other than the lead storage battery. Work in groups of 4 to do some research (textbooks, internet, etc.) to find other types of batteries. For each battery you find, make sure to describe it in the same way that I’ve described the lead storage battery: a) find a picture so we can see what it looks like in real life, b) find a schematic so we can see what the different parts of the battery are, and c) report the chemical reactions occurring in the battery. What are the similarities and differences you are finding in your batteries? How can you relate the different parts of the batteries to the galvanic/voltaic cells that we have been discussing in class?

TEST YOUR METTLE

Answer the questions related to galvanic/voltaic cells and batteries on your Blackboard homework.

GO PUBLIC

We will have a session in class where each group will make a short poster presentation to the class on a particular type of battery, how the battery works, and why the battery eventually dies.

Pre-Lesson Quiz

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