Voltaic Cells

Lesson Content

• Lesson Plan Template:

  General Lesson Plan

• Learning Objectives: What will students know and be able to do as a result of this lesson?

  
  

  Students will learn how voltaic cells are able to produce electrical energy used to do work. Students will be able to identify the different parts of a voltaic cell and calculate cell potential.

   

• Prior Knowledge: What prior knowledge should students have for this lesson?

  
  
  • Types of Reactions (including Redox)
  • Oxidation
  • Reduction
  • Redox Reactions
  • Ions (cations/anions)
  • Electrons
  • Electron Transfer
  • Electricity
  • Energy

   

• Guiding Questions: What are the guiding questions for this lesson?

  
  

  How do batteries work?

   

• Introduction: How will the teacher inform students of the intent of the lesson? How will students understand or develop an investigable question?

  
  

  Lesson opener/attention getter:

  • Have you ever wondered what's happening inside that battery that allows it to power our electronics?

  Key talking points about the lesson topic:

  • The teacher will go over the attached Voltaic Cells PowerPoint that describes the different parts of a voltaic cell and how it works. The last three slides include directions for the Flowchart activity (Your Task Part 1), the lab (Your Task Part 2), and the summative assessment (Your Task Part 3).
  • The teacher should explain prior to beginning the PowerPoint that there are many types of batteries out there and how they are set up has changed over time, but that understanding the voltaic cell is important for understanding how the batteries obtain their power from the chemicals that are found within them.

   

• Investigate: What will the teacher do to give students an opportunity to develop, try, revise, and implement their own methods to gather data?

  
  

  Instructions for setting up and helping students collect data:

  1. Students will be given a list of supplies that they can use for the lab. The students will be given a choice of chemicals with the objective of creating a cell with the highest energy output (Voltaic Cell Design Challenge). Note for instructor setup: all chemicals should be 1 M concentration.
  2. The teacher should have the students draw their setup first utilizing the directions on the last slide of the PowerPoint. If the teacher wants the students to attempt the challenge and not simply create a voltaic cell at random, they should tell the students their goal for the lab (task 2) is to create a voltaic cell with the highest energy output.

  How will you check for student understanding?

  1. Students will be asked to draw how they will set up their cell including where the chemicals will go, what chemicals they will choose to use, and the direction of electron flow. The students will also be asked to label the half-cells where oxidation and reduction occurs (anode compartment and cathode compartment).
  2. The teacher will want to check their Flowchart first to see how well the students understood the PowerPoint, then ask them to use that flowchart as a guide to help them draw their setup for their lab experiment. The teacher could choose to have the students simply add their labels of chemicals and electrodes to the flowchart instead of drawing from scratch, but I've found it's helpful to reinforce the concept of all of the components if the students use the flowchart as a guide to drawing their own.

  Common errors/misconceptions to anticipate and how to respond:

  • Students frequently have issues with labeling the anode and cathode. It is important to remind students that oxidation happens at the anode; the substance with the smaller reduction value is the oxidized species. Reduction happens at the cathode; the substance with the larger reduction value is the reduced species. The reduction values are found in the chart labeled Standard Reduction Potentials. Also, there are several elements that appear more than once, make sure you indicate to students to use the one for changing a neutral element to its ions and not a secondary ionization. For instance for copper you want them to use the value 0.34 V instead of 0.15 V.
  • Students may also have issues labeling the direction of electron flow. It is important to remind students that electrons always flow from the anode to the cathode.
  • Students usually have issues understanding the purpose of the salt bridge and the direction of anions and cations out of the salt bridge to balance the developing charges in each half-cell. It is important to remind students that cations flow out of the salt bridge toward the cathode to replace the positively charged ions that left the solution. Anions travel out of the salt bridge toward the anode in order to balance the developing positive charge in that half-cell.

   

• Analyze: How will the teacher help students determine a way to represent, analyze, and interpret the data they collect?

  
  

  Instructions to help students organize, analyze, and interpret their data:

  1. The teacher will have students test their voltaic cell designs. The students will measure their cell voltages using a voltmeter and record their voltage readings on the board. The student team whose design produced the greatest voltage wins the voltaic cell design challenge.
  2. If the students are intuitive, they will use the portion of the attached PowerPoint that explained calculating cell voltage to reverse engineer their cell setup.
  3. Students should not be penalized for not using the PowerPoint or for not doing calculations. This experiment should be more of a learning experience.

  How will you check for student understanding?

  The teacher will check for student understanding by formatively checking the challenge paper to make sure the students have their set-up correct prior to getting into the lab scenario:

  1. Substance with smaller reduction potential found in the oxidation half-cell
  2. Substance with larger reduction potential found in the reduction half-cell
  3. Oxidation half-cell labeled as anode.
  4. Reduction half-cell labeled as cathode.
  5. Electron flow shown traveling from anode to the cathode.
  6. Salt bridge drawn showing the flow of anions toward the anode and flow of cations toward the cathode.

  Common errors/misconceptions to anticipate and how to respond:

  It is important to explain to students how the voltmeter works and that they should connect the black wire to the cathode and the red wire to the anode in order to get a positive voltage reading; if the wires are connected the opposite way, they will read a negative voltage.

   

• Closure: What will the teacher do to bring the lesson to a close? How will the students make sense of the investigation?

  
  

  Instructions for leading the closing discussion:

  1. Teacher will reference student data collectively and have students identify which cell produced the most voltage/energy. That team will be announced the winner of the Voltaic Cell Design Challenge.
  2. A discussion of why their cell had the highest voltage would be appropriate (the combination of chemicals with the largest difference in standard reduction potentials should yield the highest voltage: Mg & Ag). The students could figure this out mathematically by using the standard reduction potentials table provided.

   

• Summative Assessment

  
  

  How will the students show that they met the learning objectives?

  Students will be asked to draw a voltaic cell that would produce the least amount of energy given several options of chemicals. For this assessment, there is only one correct answer (Fe & Pb) and all labeling must be done correctly to show they truly understand the setup and operation of a voltaic cell. The directions for this summative assessment are found on the last slide of the attached PowerPoint. Students must have access to the attached Standard Reductions Table and the E_cell calculation formula (from PowerPoint) to do this assessment. The correct setup for this assessment is found in the Assessment. It is important to note that the compartments (anode and cathode) can be on either side of the drawing, but all labels for those compartments should be found together (e.g. anode, oxidation, and Fe all on same side) if the compartments are the reverse, be sure to check that they labeled the arrow of electron flow pointing from the anode to the cathode. The variation in the potential drawings is shown by two illustrations in the assessment key.

   

• Formative Assessment

  
  

  Specific suggestions for conducting Formative Assessment can be found in the Investigate and Analyze phases of the lesson where it says, "How will you check for student understanding?"

   

• Feedback to Students

  
  

  Specific suggestions for providing Feedback to Students can be found in the Investigate and Analyze phases of the lesson where it says, "Common errors/misconceptions to anticipate and how to respond."