Electrochemistry and Battery Sustainability

Transcription

1 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery Science: Chemistry, Environmental Science, STEM 10th - 12th Grade Electrochemistry and Battery Sustainability Prepared By: Debbie Gaffney Overview & Purpose: Lesson 4A Simple Voltaic Cells: Electrochemistry: Electrochemistry is the study of the process by which chemical energy is converted to electrical energy. The device used for electrochemistry is called an electrochemical (voltaic) cell which uses a redox reaction to produce the electrical energy. In this lesson students will construct a voltaic cell using different metals as electrodes and measure the voltage generated with a voltmeter. This measured value is then compared to a calculated value gained from a Standard Reduction Potential table. Percent error is calculated from the differences. Several application questions are to be completed. The purpose of the lesson is for students to gain an understanding of redox reactions and their application in batteries. Battery Lesson 4B Battery Sustainability- It s a Conscious Choice: In this follow up lesson, students research different types of batteries in order to come to consensus on the most sustainable choice. In groups students research a battery focusing on the three conditions of sustainability: economic, environment and social equity. They decide on three criteria for each condition that they deem satisfies that condition of sustainability. Based on their research students than rank each of the three conditions on a triangle. The area of the triangle is calculated for each condition, resulting in the overall sustainability value for the battery. Class data is compared for an overall battery choice. Objectives: Upon completion of Lesson 4A, students will be able to Distinguish between cations and anions Identify cathode and anode Describe how a voltaic cell produces and internal and external circuit in the production of electricity Write half-reactions Calculate the cell potential using a standard reduction potential table Working in groups, students will: Do internet research on a battery type of their choice Use their data to rank their battery based on the three criteria of sustainability Rationalize their decisions and understand the perspective of others Come to a consensus in drawing conclusions Become familiar with the Sustainable Decision Grid Background Information: Lesson 4A: Electrochemistry is the study of the process by which chemical energy is converted to electrical energy. The device used for electrochemistry is called an electrochemical (voltaic) cell which uses a redox reaction to produce the electrical energy. Each voltaic cell has two electrodes, a cathode and an anode. In a voltaic cell, the half-reactions are separated into different containers known as half-cells. The half-cells are connected by a conducting wire between the two electrodes; this is called the external circuit. A salt bridge is placed between the two solutions and acts to allow the flow of negative and positive ions but does not participate in the redox reaction. This is called the external circuit and serves to maintain a charge balance. The identity of the cathode and anode during the redox reaction depends on the relative reductions potentials of the half-reactions making up the voltaic cell. The tendency of a substance to gain electrons is its reduction potential, which is measured in volts and cannot be determined directly. The standard reduction potential is abbreviated E0 and may be calculated using the table of Standard Reduction Potentials. To calculate the E0, first Science: Chemistry, Environmental Science, STEM 1

2 Lesson 1 Electrochemistry and Battery Sustainability determine the standard reduction potential for each half-cell reaction and using the equation E0cell = E0reduction E0oxidation or E0cell = E0cathode E0anode. The resulting answer is the cell s voltage measured in volts which is the equivalent of one Joule per Coulomb (1V = 1J/C). Instruction is given on writing half-reactions of each cell. Lesson 4B: The general definition of the term sustainability is meeting the needs of current generations without compromising the needs of future generations. There are three components that must be considered in order to determine if a choice or decision is sustainable. They are the areas of economic, environmental, and social equity. Each area may be further defined as follows: Economic: factors may include, but not limited to, jobs, costs, labor hours, etc. Environment: factors may include, but not limited to, air and water quality, habitat conservation, environmental justice, safety, options for recycling, etc. Social equity: factors may include, but not limited to, diversity in populations affected, number of people positively impacted, increases in lifestyle benefits, etc. Students research each criterion and then rank them based on the decided sustainability. The rankings are plotted on a triangle; each side of the triangle represents one of the criteria. The area of the triangle is calculated which represents the sustainability of that battery type. Group data is presented to the class which then decides on the overall sustainable battery type. Performance Expectation(s) HS-PS3-5: Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction. Classroom Activities/Procedures & Timeline (3-4 days) Lesson 4A: Each metal electrode (Zn, Cu, Fe and Pb) is cleaned with sandpaper until it is shiny. 20 ml of each solution is placed in separate beakers and labelled. Four strips of filter paper are dipped into a solution of potassium nitrate. Arrange the beakers of solution so that the KNO3 beaker is in the center and the other beakers of solution are arranged around it in a circle. Remove a strip of filter paper from the beaker and place one end in the KNO3beaker and the other end in another beaker. Make sure both ends are submerged in each solution. This is the salt bridge. Do this with separate strips of saturated filter paper to each of the other beakers containing solution. A voltmeter is set up and zeroed. Each electrode is placed in its corresponding solution. An alligator clip is connected to one end of an electrode with the other end connected to the lead of the voltmeter. The same procedure is performed to another electrode in the other solution. The first steady reading from the voltmeter is recorded as the electron potential of the cell. This procedure continued until all combinations of electrodes has been tested. Anode and cathode are identified in each case and half-reactions are written. The potential of the cell is calculated and percent error is determined. This lab may be completed in one class period though additional time may be needed to write reactions and answer questions. Lesson 4B: A battery to research is chosen from a provided list. In groups students collect data on their battery in three areas in order to rank the battery s sustainability. The three areas are economics, environment and social equity. As a group they decide Equipment/Materials/ Technology Needed: Lesson 4A : Materials per lab group: One strip of each electrode metal: Fe, Zn, Pb, Cu Sandpaper Four strips of filter paper Tweezers 20 ml of each solution: FeCl3, Zn(NO3)2, Pb(NO3)2, KNO3, Cu(NO3)2 5 beakers ( 250mL or smaller) Alligator leads Voltmeter Lesson 4B : Materials Class set of computers with internet access Copies for each student of the Decision Grid Student Sheet 2 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

3 Rubric Grade on three conditions that must be satisfied in order to conclude their battery has met the criterion for sustainability. In the Table for Ranking they need to list the three conditions that the group will use to identify that each criteria has been met. For example in the area of economics, they may decide to focus on the cost to produce the battery, the pay that workers receive and the hours required to produce the battery in making the decision it is sustainable for economics. Websites are suggested to use during research. Data is recorded in three separate tables. The decision grid for each of the three criteria is ranked using a provided scale: 3 Meets all or nearly all of the criterion, 2 Meets most of the criterion, 1 Meets some of the criterion, 0 Meets little, if any of the criterion. The rankings are plotted on sides of a triangle and the resulting area is calculated. The battery s sustainability is quantized as the area of the triangle. Each group s battery area is then compared to the class and a class consensus is determined for the most sustainable battery type. This lesson requires two class periods, one day to do the research and a second day to rank and plot data on triangle. Depending on the class, an additional day may be needed for discussion and class determination of the overall most sustainable battery. Assessments: (e.g., lab, quiz, test, oral presentation, survey, rubric, etc.) Lesson 4A Formative Assessment Teacher moves around each group and asks students to identify the cathode and anode and various other components of their battery. Teacher gives descriptive feedback to direct students to understanding. Questions concerning changing variables may be asked as well, such as predicting the effect of changing the concentration of the solutions on the voltage observed. Have each student write a narrative describing and explaining what occurs in an electrochemical cell. Components to assess should include correct use of terminology, understanding of electron flow and both internal and external circuits as well as the processes occurring at each electrode. Diagram of electrochemical cell, labeling all parts involved in the process. Laboratory Assessment Provide students with two unknown metals and matching solutions. Have them determine the cell potential of the electrochemical cell produced, using the same procedure as performed in the lab. Provide students with groups of metals, test tubes and solutions. Have them determine the order of reduction potentials without creating voltaic cells. This is similar to producing an activity series of single-replacement reactions, only in reverse. Otherwise, assessment is made from participation, completion of lab questions and data chart. Included are analogies and misconceptions that the teacher may choose to use as a discussion or as a measure of prior knowledge. Students may be asked to diagram or write their own analogies of how a voltaic cell works. Lesson 4B: Assessment Active participation in research and class discussions Group self-evaluation Completion of Student Decision Grid worksheet Teacher Resources: (e.g., readings, set-up instructions, lecture files, data files, etc.): Sections are included in the lesson : Extensive explanation of redox reactions, electrochemical cells and how to calculate cell potential A Standard Reduction Potential Table Definition to the pre-lab vocabulary Solution preparation Examples of analogies for current and potential energy Addressing student misconceptions Applications of electrochemistry The Keystone Center for Education, Systems Thinking and Sustainability: Triangle Triage The Decision Grid. Websites: watch?v=l9niwvnpoxi Galvanic Cell Battery Lab article/what_the_best_battery pdf/batterytypes.pdf rechargeable.html BatteryTypes/ Student Resources: (e.g., handouts, worksheets, data, etc.): A copy of the student handout is included with each lesson. An explanation of the activities is also included. Data charts for collecting data and a Standard Reduction Potential table is included. The equation for calculating the area of a triangle is included as well as data charts for listing each criteria. A triangle formatted with criteria on each side is provided for plotting data rankings. Suggested websites are listed. Science: Chemistry, Environmental Science, STEM 3

4 Unit 1 Electrochemistry and Battery Sustainability Extensions/Homework: Lesson 4A: The voltaic cells may be connected together to produce more Voltage. As an interesting inquiry process, students may try to diagram how to connect the cells in series in order to increase the voltage. Additionally, motors and other electrical devices may be connected via alligator clips. Analyzing effects of concentrations of solutions is also an option of study. Lesson 4B: As an extension, students may research an individual battery type and construct a presentation for the class. A scientific argument may also be written and presented as part of a class debate in determining an overall sustainable battery type. References: Lesson 4A: ChemSource Instructional Resources for Preservice and Inservice Chemistry Teachers. Electrochemistry: A SourceBook Module, Version 1.0, Website: Galvanic Cell Battery Lab Lesson 4B: The Keystone Center for Education, Systems Thinking and Sustainability: Triangle Triage The Decision Grid Kim Villani, use of her Decision Grid worksheet Websites Equipment/Materials/ Technology Needed: Lesson 4A : Materials per lab group: One strip of each electrode metal: Fe, Zn, Pb, Cu Sandpaper Four strips of filter paper Tweezers 20 ml of each solution: FeCl3, Zn(NO3)2, Pb(NO3)2, KNO3, Cu(NO3)2 5 beakers ( 250mL or smaller) Alligator leads Voltmeter Lesson 4B : Materials Class set of computers with internet access Copies for each student of the Decision Grid Student Sheet Accommodations & Safety Concerns: Lesson 4A: Goggles should be worn at all times when handling chemicals. A microscale version is suggested for students who require accommodations. Lesson 4B: No safety concerns in carrying out the lesson. All students are capable of performing the activity. Personal Comments/Notes: Lesson 4A lends itself to a great inquiry lesson. My experience with the lesson had students trying to construct bigger voltaic cell by connecting them together. Quite a bit of discussion and thinking arose in trying to decide how to connect and what to actually connect in order to complete a circuit and keep voltage measurable. The applications of this lesson are broad. Lesson 4B is a great method of aiding students in making decisions as a group. The triangle decision grid method is a versatile way of quantitatively rating decisions that students seem to enjoy and understand. 4 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

5 Teacher Activity Copy - Activity Sheet Sheet Grade NGSS: HS-PS3-5 Energy Teacher Copy Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery HS-PS3-5: Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction. Science and Engineering Practices: Developing and Using Models: Developing models to predict and show relationships among variables between systems and their components in the natural and designed world. Develop and use a model based on evidence to illustrate the relationships between systems or between components of systems. Disciplinary Core Ideas: PS3.C: Relationship Between Energy and Forces When two objects interacting through a field change relative positive, the energy stored in the field is changed. Crosscutting Concepts: Cause and Effect Cause and effect relationships can be suggested and predicted for complex natural and human designed systems by examining what is known about smaller scale mechanisms within the system. Common Core State Standards Connections: ELA/Literacy WHST : Conduct a short as well as more sustained research projects to answer a question (including self-generated question) or solve a problem; narrow or broaden the inquiry when appropriate; synthesize multiple sources on the subject, demonstrating understanding of the subject under investigation. WHST : Gather relevant information from multiple authoritative print and digital sources, using advanced searches effectively; assess the strengths and limitations of each source in terms of the specific task, purpose, and audience; integrate information into the text selectively to maintain the flow of ideas, avoiding plagiarism and overreliance on any one source and following a standard format for citation. WHST : Draw evidence from information texts to support analysis, refection and research. SL : Make strategic use of digital media in presentations to enhance understanding of findings, reasoning and evidence and to add interest. Mathematics: MP.2: Reason abstractly and quantitatively. MP.4: Model with mathematics Science: Chemistry, Environmental Science, STEM 5

6 Unit 1 Electrochemistry and Battery Sustainability Lesson 4A Title: Simple Voltaic Cells: Electrochemistry Teacher Copy Student Background Information Students should be familiar with single replacement reactions and the activity series of metals. Students need to understand basic vocabulary words such as anode, cathode, oxidation and reduction. Students should be able to calculate oxidation numbers of reaction species. Students should have a general understanding of basic concepts of energy, conductivity in ionic solutions and the behavior of charged particles. Basic mathematical skills are required in calculating reduction cell potentials. This first laboratory is to allow students to gather data and become familiar with voltaic cells. Introduction Of all the types of chemical reactions perhaps the more important is oxidation-reduction. Many previously learned reaction types are oxidation-reduction reactions, like all single replacement and combustion reactions. Many synthesis and decomposition reactions are also oxidation-reduction. The key to being an oxidation-reduction reaction is the transfer of electrons or the ability of one substance involved in the reaction to lose electrons and the other substance having the potential to accept these electrons. The oxidation-reduction reaction may be broken into two separate reactions, the oxidation process and the reduction process. Both must always occur together and the electrons lost must always equal the electrons gained. During the process of oxidation, electrons are lost while electrons are gained during reduction. A memory aid is LEO goes GER which stands for Loss of Electrons is Oxidation and Gain of Electrons is Reduction. Another way to think of this is that when electrons are gained the oxidation number of the ion becomes more negative or is reduced numerically. These two reactions are referred to as half-reactions and the number of electrons moving between must be equal. Whether a specific oxidation-reduction reaction occurs depends on the reduction potential of the two reacting species. Reduction potential is the force behind a reduction reaction and therefore redox reactions proceed in the direction of the species gaining electrons. As a result, the half-reaction with the larger reduction potential will occur as reduction and the half-reaction with the smaller reduction potential will proceed as an oxidation reaction; its electrons will be lost to the species with the greater potential. Different elements lose or accept electrons easier than others. As a result, elements may be organized by their relative ability to undergo reduction (gain/accept) reactions. The result is called the Table of Standard Reduction Potentials and is arranged based on an element s ability to accept (be reduced) electrons from a standard donor of hydrogen. The highest reduction potential belongs to fluorine, with metals typically having the lowest potential of being reduced. As such, the difference in reduction potentials between two elements in a redox reaction is an indication of the force behind the electron transfer. In a voltaic cell, this difference is the cell s potential and is equal to the electric potential for a standard cell battery. So by subtracting the reduction potentials of the reacting species, it is possible to calculate the electric potential for a battery and therefore determine the amount of electrical energy available for work. Electrochemistry is the study of the process by which chemical energy is converted to electrical energy. The device used for electrochemistry is called an electrochemical cell which uses a redox reaction to produce the electrical energy. A specific type of electrochemical cell is a voltaic cell, named for Alessandro Volta the Italian physicist credited for its invention. In a voltaic cell the redox reaction occurs spontaneously. 6 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

7 Teacher Copy Grade Voltaic Cell Basics The standard way to compare half-reactions is using a voltaic cell. Each voltaic cell has two electrodes, a cathode and an anode. Reduction reactions always occur at the cathode, meaning electrons are being accepted and oxidation reactions always occur at the anode, where electrons are lost. A memory device is oxidation and anode both starts with a vowel and reduction and cathode both starts with consonants. The cathode is positively charged which allows it to accept electrons and the anode is negatively charged. The identity of the cathode and anode during the redox reaction depends on the relative reductions potentials of the half-reactions making up the voltaic cell. The cathode in the cell is always the electrode with the more positive reduction potential and the anode is the electrode with the less positive reduction potential. This explains the electric potential of the cell. Electrical potential energy is a measure of the amount of current generated by the voltaic cell to do work, so electric charge can flow between two points only when there is a difference in electrical potential energy between the two points. The electrodes are the two points. In a voltaic cell, the half-reactions are separated into different containers known as half-cells. The half-cells are connected by a conducting wire between the two electrodes; this is called the external circuit. A salt bridge is placed between the two solutions and acts to allow the flow of negative and positive ions but does not participate in the redox reaction. This is called the internal circuit. A salt bridge is typically a tube filled with a conducting solution of a soluble salt such as KCl or KNO 3. The salt may be held in place in the tube with agar gel which allows the free flow of electrons but keeps the two solutions in the cells separated. The purpose of the salt bridge is to prevent the buildup of positive and negative charges in each individual solution. When electrons flow from a half-cell through the external circuit, negative ions travel to that half-cell in order to maintain electrical neutrality. Conversely, when electrons flow into the other half-cell, positive ions travel to that half-cell to ensure electrical neutrality there as well. The accumulation of positive charges in one solution prevents oxidation from occurring and the buildup of negative charges in the other solution prevents reduction. The salt bridge keeps the charges in each solution such that the redox reaction occurs; in other words, charge is conserved by the salt bridge. So, a voltaic cell has two circuits, an internal and an external. When both are in place, electrons flow through the connecting wire (external) from the oxidation half reaction to the reduction half-reaction while positive and negative ions move through the salt bridge. Both circuits make up the electric current whose energy may be used to light a light bulb or run an electric motor. Calculating Electrochemical Cell Potential The tendency of a substance to gain electrons is its reduction potential, which is measured in volts and cannot be determined directly. Why can t it be determined directly? This is due to the fact that a reduction half-reaction must be coupled to an oxidation half-reaction. When the two reactions are coupled the voltage corresponds to the difference in potential between the two half-reactions. The standard reduction potential is abbreviated E 0 and may be calculated using the table of Standard Reduction Potentials. Though the table is written as reductions, the half-reaction with the lower reduction potential will proceed as an oxidation reaction and the more positive potential will proceed as a reduction. To calculate the E 0, first determine the standard reduction potential for each half-cell reaction and using the equation E 0 cell = E0 reduction E0 oxidation or E 0 cell = E0 cathode E0 anode. The resulting answer is the cell s voltage measured in volts which is the equivalent of one Joule per Coulomb (1V = 1J/C). Science: Chemistry, Environmental Science, STEM 7

8 Unit 1 Electrochemistry and Battery Sustainability Figure 1. The anode half-cell consists of a zinc electrode submerged into a solution containing Zn 2 + ions (e.g. aqueous Zn(NO 3 ) 2 ), while the cathode half-cell consists of a copper electrode submerged in a solution of Cu 2 + ions (e.g. aqueous Cu(NO 3 ) 2 ). Oxidation occurs at the anode as each zinc atom loses two electrons to form aqueous Zn 2 +, thus decreasing the mass of the anode as oxidation occurs. These electrons move through the zinc electrode, the wire and voltmeter on to the copper electrode submerged in the solution of Cu 2 + ions. Finally, reduction occurs on the surface of the cathode as the electrons react with the Cu 2 + ions in solution to form solid copper metal which plates out on the surface of the cathode, thereby increasing the cathode s mass in the process. A salt bridge contains unreactive sodium ions (Na+) and sulfate ions (SO 42- ) that maintain neutral charge in the electrolyte solution: Anions in the salt bridge flow to the left, and cations to the right. The voltmeter measures the electrical output of the cell. Since zinc is above copper on the activity series, zinc is more easily oxidized than copper. Consequently, the electrical current flows from the zinc electrode (anode) to copper electrode (cathode). Looking at reduction potentials, since the reduction potential of Zn 2 + (-0.76 V) is more negative than that of Cu 2 + ( V), zinc is more easily oxidized. (Lab 8 - Chemistry K. Marr, Green River Community College) 8 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

9 Teacher Copy - Activity Sheet Grade Calculating an E 0 cell is shown in the example below: The use of standard reduction potentials to predict the potential of the voltaic cell in Figure 1 is illustrated below. Reduction reactions: E 0 Zn 2 + (aq) + 2e- r Zn(s) (more negative potential, therefore the anode) Cu 2 + (aq) + 2e- r Cu(s) (more positive potential, therefore the cathode) Cathode: Cu 2 +(aq) + 2e- r Cu(s) Anode: Zn(s) r Zn2+(aq) + 2e- Cell Reaction: Cu 2 +(aq) + Zn(s) r Zn 2 +(aq) + Cu(s) E 0 cell = E0 cathode - E0 anode E 0 cell = +0.34V (-0.76V) = 1.10V If the potential that is measured is not from a standard cell (at 25 C, 1atm using 1Molar solutions), then the Nerst equation may be used to calculate the standard cell potential. The equation is given below; however the differences are too insignificant to be concerned about, unless the class is capable of using the equation. Nerst equation: E cell = E 0 cell V/n lne Where: n = number of electrons transferred in cell reaction Q = reaction quotient, concentration of anode divided by concentration of cathode E 0 = standard cell potential calculated from table E cell = cell potential at nonstandard conditions The calculated potential of a voltaic cell may be used to determine if a redox reaction will occur spontaneously. If after subtracting each half-cell s reduction potential, the voltaic cell s potential is positive then the redox reaction will occur spontaneously; if the difference is negative, then the redox reaction is not spontaneous. However, the negative nonspontaneous redox reaction will be spontaneous in reverse. If the redox reaction is spontaneous and the two half-reactions are separated by a wire, then the electron flow occurs at the external wire instead of occurring at the surface of the metal electrode and an electric current is generated. The resulting voltaic cell is exactly how a battery functions. Batteries contain both oxidizing and reducing substances. As electrons are transferred, they are selected in order to supply voltage to power a flashlight or calculator. To summarize, the field of electrochemistry has two important applications, the use of spontaneous redox reactions to generate electricity, and the use of electricity to force non spontaneous redox reactions to occur. Before conducting the laboratory it is suggested that students be familiar with the following vocabulary words. Teachers may opt to assign the words or discuss them together in preceding classes. Science: Chemistry, Environmental Science, STEM 9

10 Lesson 1 Electrochemistry and Battery Sustainability Pre-Lab Vocabulary: 1 Oxidation: a reaction where electrons are lost 2 Reduction: a reaction where electrons are gained 3 Anode: the electrode where electrons are lost; has the more negative reduction potential 4 Cathode: the electrode where electrons are gained, has the more positive reduction potential 5 Half-reactions: reaction that represents each oxidation or reduction process 6 Electrochemical cell: a device in which electrons of a redox reaction pass through an electrical circuit 7 Half-cell: combination of reduced and oxidized forms of a given species upon which redox equilibrium is established 8 Battery: voltaic cell used to produce electricity through chemical reaction 9 Voltaic cell (Galvanic cell): electrochemical cell in which a spontaneous chemical reaction produces electricity 10 Electromotive force (EMF): synonym for cell potential 11 Cell potential (cell voltage/electric potential): potential difference in volts of a electrochemical cell 12 Salt bridge: device used to join two half-cells and containing a salt solution that permits the flow of ions between two half-cells Preparing Solutions (for 24 students working in pairs) 0.1M iron III chloride FeCl 3 : dissolve 8.11 grams in water to make 500 ml of solution 0.1M zinc nitrate Zn(NO 3 ) 2 : dissolve 9.47 grams in water to make 500 ml of solution 0.1M lead II nitrate Pb(NO 3 ) 2 : dissolve grams in water to make 500 ml of solution 0.1M potassium nitrate KNO 3 : dissolve 5.06 grams in water to make 500 ml of solution 0.1M copper II nitrate Cu(NO 3 ) 2 : dissolve 9.15 grams in water to make 500 ml of solution Addressing Student Misconceptions 1 Electrons do not flow through the solutions of the half cells. The charge balance is maintained in the solutions by movement of cations and anions. The ions are able to move through the salt bridge toward separated electrodes where charge transfer takes place at the interface of the solution/electrode. 2 Water is not a good conductor of electricity. Water is actually a poor conductor of electricity but is an excellent solvent for ionic compounds. It is the dissolved ions that enable water to be conductive. Ions in solution carry the charge and are responsible for the current not the water. 10 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

11 Teacher Copy - Activity Sheet Rubric Grade 9-10 Useful Analogies Work done by a voltaic cell is similar to a water wheel powered by falling water. The height from which the water falls is analogous to the cell potential. The higher the water falls, the more potential energy it possesses. The higher the cell potential in a voltaic cell, the more pushing force available for the electrons. The amount (volume) of water falling over the water wheel is analogous to the current generated by a voltaic cell. The amount of work depends on how much water flows per second over the water wheel (analogous to current) and the height from which the water falls (analogous to electric potential). Applications of Electrochemistry 1 Cathodic protection of iron from corrosion. Iron is used quite frequently in construction, ship hulls and in underground storage tanks. It will corrode (oxidize) unless it is protected. Applying a coat of paint is not effective in the long term because it may chip or become scratched, exposing the iron to the environment. Instead a more effective method is to attach a piece of zinc to it. Zinc oxidizes easier than iron, meaning it has a more positive reduction potential than iron. Zinc becomes the sacrificial cathode. 2 Dental filling discomfort. Dentists fill decayed teeth with dental amalgam. An amalgam is a substance made from combining mercury with other metals. Typically these other metals are silver and tin. The three solid phases and standard reduction potentials are: Hg / Ag +, 0.85V, Sn 2 + / Ag +, -0.05V, Sn 2 + / Hg, -0.13V. Biting onto a piece of aluminum foil causing the foil to come into contact with the filling causes pain. Basically, an electrochemical cell has been created in the mouth with aluminum, with a standard potential of -1.66V acting as the anode, the amalgam acting as the cathode and saliva is the electrolyte. The contact between the foil and the filling short-circuits the electrochemical cell, causing a weak current between the electrodes, which stimulates the nerve of the tooth. 3 Corrosion of a dental filling. Additionally, discomfort may occur if a filling makes contact with a gold inlay on another tooth. In this type of contact, the filling acts as the anode, the gold inlay acts as the cathode, resulting in the filling being corroded. Most noticeably the corrosion causes a release of tin II ions in the mouth which produces an unpleasant metallic taste. Purpose The purpose of this lesson is for students to gain an understanding of redox reactions, the associated terminology and application as batteries. Objectives Upon completion of this laboratory, students will: Be able to distinguish between cations and anions Be able to identify cathode and anode Be able to describe how a voltaic cell produces an internal and external circuit in the production of electricity Be able to write half-reactions Be able to calculate the cell potential using a standard reduction potential table Safety: Goggles must be worn at all times. Handle chemicals with care. Science: Chemistry, Environmental Science, STEM 11

12 Lesson 1 Electrochemistry and Battery Sustainability Materials per lab group: One strip of each electrode metal: Fe, Zn, Pb, Cu Sandpaper Four strips of filter paper Tweezers 20 ml of each solution: FeCl 3, Zn(NO 3 ) 2, Pb(NO 3 ) 2, KNO 3, Cu(NO 3 ) 2 5 beakers ( 250mL or smaller) Alligator leads Voltmeter Pre-Lab It is recommended that teachers familiarize students with the lab the day before. Students should certainly understand the vocabulary words in order to use them correctly during the lab. The solutions should be made in advance and all materials gathered prior to the day of the lab. The YouTube video is an excellent way of introducing students to the actual procedures and is only four minutes in length. Stations may be set up for a more organized means of gathering materials, as there are quite a few to measure out before setting up the actual wet cell battery. The lab may be performed as a mini-experiment using well plates, but the metals are difficult to keep in such a small well and the larger set up seems to be more dramatic and allows students to extend the process by connecting several student cells together. My experience is that the students tend to perceive the larger set up as more battery-like and they instantly wanted to try to build it bigger and produce more voltage by connecting several together. It was an interesting inquiry process as student tried to diagram and visualize how to connect the cells in series and much discussion was had in trying to decide what exactly needed to be connected to what in order to increase the voltage. Certainly, this is encouraged and may require an additional day of inquiry. Additional equipment may be needed for extension activities, such as mini-light bulbs and holders, extra alligator clips and motors. Procedures: 1 Clean each metal electrode using the sandpaper until each is shiny. 2 Measure 20 ml of each solution and place in a separate beaker labelled with the solutions formula. 3 Soak each strip of filter paper in the KNO 3 solution until it is saturated but not dripping. 4 Arrange the beakers of solution so that the KNO 3 beaker is in the center and the other beakers of solution are arranged around it in a circle. 5 Using tweezers, remove a strip of filter paper from the beaker and place one end in the KNO 3 beaker and the other end in the Pb(NO 3 ) 2 beaker. Make sure both ends are submerged in each solution. This is the salt bridge. Do this with separate strips of saturated filter paper to each of the other beakers containing solution. 6 Set up the voltmeter by turning it on and setting it to zero. Turn the dial to the setting volts DC represented by the V with dashed lines. The red lead is the positive terminal and the black lead is the ground or COM terminal. 7 Ready! Place each electrode in its corresponding solution, zinc in Zn(NO 3 ) 2, lead in Pb(NO 3 ) 2, copper in Cu(NO 3 ) 2 and iron in FeCl 3. 8 Choose where to start by selecting two solutions to test. 9 Connect the electrode in one solution to one end of the alligator clip and the other end of the alligator clip to the lead from the voltmeter. Do the same to the other electrode in the other solution. If you get a negative reading on the voltmeter you need to switch the leads (they re backwards for the reaction). 12 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

13 Teacher Copy - Activity Sheet Grade Record your first steady reading from the voltmeter. This is the electron potential for the cell. 11 Rinse off each electrode thoroughly before placing into another solution and before finishing the lab. Data Table Cell Anode Cathode Cell Potential Measured (volts) Theoretical Potential Calculated (volts) Percent Error Half-reactions and Potentials Anode Half - Reaction Cathode Half-Reaction 1 2 Science: Chemistry, Environmental Science, STEM 13

14 Unit 1 Electrochemistry and Battery Sustainability Anode Half - Reaction Cathode Half-Reaction Discussion Questions 1 Draw a complete voltaic cell using one of the anode - cathode combinations from the lab. Label the electrodes, salt bridge, the sign of each electrode and where oxidation and reduction will occur. Using arrows show the direction of flow for electrons between the half-cells. 2 What is the role of electrons in oxidation-reduction reactions? Electrons are exchanged during oxidation-reduction producing the electromotive force, moving from oxidized to reduced species. 3 How can a chemical reaction be used to produce electricity? By connecting the half-cells of a redox reaction that are physically separated by a salt bridge. This completes the internal circuit which then allows ions to flow between the two cells. The external connection is made by connecting the electrodes together to allow movement of electrons, producing the current. 4 Rank the metals used in order of most active to least active. 14 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

15 Teacher Copy - Activity Sheet Grade Why do you suppose lithium batteries are becoming popular for use in pacemakers? (Hint: use the Standard Reduction Potential table). Lithium has the lowest reduction potential on the table, meaning it does not gain electrons. This makes it a very effective, long-lasting supplier of electrons, which is needed in a long-term battery. 6 Why must salt bridges be in contact with both solutions for the voltaic cell to generate current? This contact allows the flow of cations and anions to their corresponding electrodes, thereby allowing the electrons to keep being generated and flowing through the connecting wire. 7 In 1973, the wreckage of the Civil War ironclad USS Monitor was discovered near North Carolina. In 1987, investigations were begun to determine a means of salvaging the ship. Using your knowledge of electrochemistry, what would you do to prevent further corrosion of the ship? Explain your decision. Zinc electrodes could be attached to the ship to prevent corrosion. Zinc undergoes corrosion more readily than iron. Assessment Formative assessment Teacher moves around each group and asks students to identify the cathode and anode and various other components of their battery. Teacher gives descriptive feedback to direct students to understanding. Questions concerning changing variables may be asked as well, such as predicting the effect of changing the concentration of the solutions on the voltage observed. Have each student write a narrative describing and explaining what occurs in an electrochemical cell. Components to assess should include correct use of terminology, understanding of electron flow and both internal and external circuits as well as the processes occurring at each electrode. Diagram of electrochemical cell, labeling all parts involved in the process. Laboratory Assessment Provide students with two unknown metals and matching solutions. Have them determine the cell potential of the electrochemical cell produced, using the same procedure as performed in the lab. Provide students with groups of metals, test tubes and solutions. Have them determine the order of reduction potentials without creating voltaic cells. This is similar to producing an activity series of single-replacement reactions, only in reverse. Otherwise, assessment is made from participation, completion of lab questions and data chart. References ChemSource Instructional Resources for Preservice and Inservice Chemistry Teachers. Electrochemistry: A SourceBook Module, Version 1.0, Website: Galvanic Cell Battery Lab Science: Chemistry, Environmental Science, STEM 15

16 Lesson Electrochemistry: 1 Constructing a Battery and Deciding on a Sustainable Battery Student Copy Pre-Lab Vocabulary: 1 Oxidation: 2 Reduction: 3 Anode: 4 Cathode: 5 Half-reactions: 6 Electrochemical cell: 7 Half-cell: 8 Battery: 9 Voltaic cell (Galvanic cell): 10 Electromotive force (EMF): 11 Cell potential (cell voltage/electric potential): 12 Salt bridge: Objectives Upon completion of this laboratory, students will: Be able to distinguish between cations and anions Be able to identify cathode and anode Be able to describe how a voltaic cell produces an internal and external circuit in the production of electricity Be able to write half-reactions Be able to calculate the cell potential using a standard reduction potential table Safety: Goggles must be worn at all times. Handle chemicals with care. 16 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

17 Student Copy Rubric - Activity Sheet Grade Materials per lab group: One strip of each electrode metal: Fe, Zn, Pb, Cu Sandpaper Four strips of filter paper Tweezers 20 ml of each solution: FeCl 3, Zn(NO 3 ) 2, Pb(NO 3 ) 2, KNO 3, Cu(NO 3 ) 2 5 beakers ( 250mL or smaller) Alligator leads Voltmeter Procedures: 1 Clean each metal electrode using the sandpaper until each is shiny. 2 Measure 20 ml of each solution and place in a separate beaker labelled with the solutions formula. 3 Soak each strip of filter paper in the KNO 3 solution until it is saturated but not dripping. 4 Arrange the beakers of solution so that the KNO 3 beaker is in the center and the other beakers of solution are arranged around it in a circle. 5 Using tweezers, remove a strip of filter paper from the beaker and place one end in the KNO 3 beaker and the other end in the Pb(NO 3 ) 2 beaker. Make sure both ends are submerged in each solution. This is the salt bridge. Do this with separate strips of saturated filter paper to each of the other beakers containing solution. 6 Set up the voltmeter by turning it on and setting it to zero. Turn the dial to the setting volts DC represented by the V with dashed lines. The red lead is the positive terminal and the black lead is the ground or COM terminal. 7 Ready! Place each electrode in its corresponding solution, zinc in Zn(NO 3 ) 2, lead in Pb(NO 3 ) 2, copper in Cu(NO 3 ) 2 and iron in FeCl 3. 8 Choose where to start by selecting two solutions to test. 9 Connect the electrode in one solution to one end of the alligator clip and the other end of the alligator clip to the lead from the voltmeter. Do the same to the other electrode in the other solution. If you get a negative reading on the voltmeter you need to switch the leads (they re backwards for the reaction). 10 Record your first steady reading from the voltmeter. This is the electron potential for the cell. 11 Rinse off each electrode thoroughly before placing into another solution and before finishing the lab. Science: Chemistry, Environmental Science, STEM 17

18 Lesson 1 Electrochemistry and Battery Sustainability Half-reactions and Potentials Anode Half - Reaction Cathode Half-Reaction 1 2 Anode Half - Reaction Cathode Half-Reaction Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

19 Student Rubric - Activity Sheet Grade Data Table Cell Anode Cathode Cell Potential Measured (volts) Theoretical Potential Calculated (volts) Percent Error 1 Draw a complete voltaic cell using one of the anode - cathode combinations from the lab. Label the electrodes, salt bridge, the sign of each electrode and where oxidation and reduction will occur. Using arrows show the direction of flow for electrons between the half-cells. 2 What is the role of electrons in oxidation-reduction reactions? 3 How can a chemical reaction be used to produce electricity? Science: Chemistry, Environmental Science, STEM 19

20 Lesson 1 Electrochemistry and Battery Sustainability 4 Rank the metals used in order of most active to least active. 5 Why do you suppose lithium batteries are becoming popular for use in pacemakers? (Hint: use the Standard Reduction Potential table). 6 Why must salt bridges be in contact with both solutions for the voltaic cell to generate current? 7 In 1973, the wreckage of the Civil War ironclad USS Monitor was discovered near North Carolina. In 1987, investigations were begun to determine a means of salvaging the ship. Using your knowledge of electrochemistry, what would you do to prevent further corrosion of the ship? Explain your decision. 8 Using complete sentences, thoroughly describe the processes that occur in an electrochemical cell, being sure to use correct terminology. Describe how electricity is generated. 20 Energy Types and Sources

21 Lesson 4B Rubric - Teacher Copy Grade Battery Sustainability: It s a Conscious Choice Background Information The general definition of the term sustainability is meeting the needs of current generations without compromising the needs of future generations. There are three components that must be considered in order to determine if a choice or decision is sustainable. They are the areas of economic, environmental, and social equity. Each area may be further defined as follows: Economic: factors may include, but not limited to, jobs, costs, labor hours, etc. Environment: factors may include, but not limited to, air and water quality, habitat conservation, environmental justice, safety, options for recycling, etc. Social equity: factors may include, but not limited to, diversity in populations affected, number of people positively impacted, increases in lifestyle benefits, etc. Purpose The purpose of the lesson is to increase student knowledge and understanding about the different battery types and come to a consensus about battery sustainability using a technique known as Sustainable Decision Grid. Objectives Working in groups, students will: Do internet research on a battery type of their choice Use their data to rank their battery based on the three criteria of sustainability Rationalize their decisions and understand the perspective of others Come to a consensus in drawing conclusions Become familiar with the Sustainable Decision Grid Materials Class set of computers with internet access Copies for each student of the Decision Grid Student Sheet Procedure Day 1 Instruct students to get into groups of 3 4 students Explain to students they are to select a type of battery from the list given and to conduct internet research Instruct students that they are to record the information they collect in the table provided Explain to students they are to use the websites provided on their Student Sheet, but they may also find other appropriate sites as well Tell students they are to keep a record of all the sources they use Discuss with students the three criteria they are to focus on, economic, environment, social equity, when conducting their research; you may suggest to students that they assign individual members within their group a single criteria to focus on Discuss with students how they will identify if criteria are met. For example what criteria will they use to recognize that Science: Chemistry, Environmental Science, STEM 21

22 Lesson 1 Electrochemistry and Battery Sustainability a type of battery has met the standard for economics? Have students identify three criteria they will use for each component of sustainability before they begin research. Give students examples of what may be important in each standard, for example: o Economics: improves the standard of living o Social equity: accessible to everyone o Environment: resources are not impacted Day 2 In the same group as Day 1, students will complete a decision grid for their battery type Explain to students they are to come to consensus for each criteria using the rating scale given and then plot the ranking on the appropriate leg of the triangle Once each group has constructed a triangle representing their ranking of their battery, they will calculate the area of the triangle Students will then compare areas of each battery type as a class in order to identify the most sustainable battery as decided by the class Assessment Active participation in research and class discussions Group evaluation Completion of Student Decision Grid worksheet References The Keystone Center for Education, Systems Thinking and Sustainability: Triangle Triage The Decision Grid. Kim Villani, use of her Decision Grid worksheet Websites Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

23 Battery Sustainability: Rubric It s a Conscious Choice Grade Student Decision Grid Name: BATTERY TYPE Day 1 Background Information The general definition of the term sustainability is meeting the needs of current generations without compromising the needs of future generations. There are three components that must be considered in order to determine if a choice or decision is sustainable. They are the areas of economic, environmental, and social equity. Each area may be further defined as follows: Economic: factors may include, but not limited to, jobs, costs, labor hours, etc. Environment: factors may include, but not limited to, air and water quality, habitat conservation, environmental justice, safety, options for recycling, etc. Social equity: factors may include, but not limited to, diversity in populations affected, number of people positively impacted, increases in lifestyle benefits, etc. Purpose The purpose of the lesson is to increase your knowledge and understanding about the different battery types. As a group, you are to come to a consensus about your battery s sustainability based on three criteria, economics, environment and social equity. You will then present your decision to the class and as a class decide on the most sustainable battery type overall. Objectives Working in groups, you will: Do internet research on a battery type of their choice Use your data to rank your battery based on the three criteria of sustainability Rationalize your decisions while understanding the perspective of others Come to a consensus using the Sustainable Decision Grid as a guide Materials Computer with internet access Copy of the Decision Grid Student Sheet Science: Chemistry, Environmental Science, STEM 23

24 Lesson 1 Electrochemistry and Battery Sustainability Day 1 Procedures Choose a battery to research from the following list. As a group you will collect data on your battery in three areas in order to rank the battery s sustainability. The three areas are economics, environment and social equity. You need to decide as a group three conditions that must be satisfied in order to conclude your battery has met the criterion for sustainability. In the Table for Ranking you need to list the three conditions that your group will use to identify that each criteria has been met. For example in the area of economics, you may decide to focus on the cost to produce the battery, the pay that workers receive and the hours required to produce the battery in making the decision it is sustainable for economics. Decide on and list the three conditions for each criterion before you begin. Record your data collected. List of Battery Types (select one to research) Zinc carbon Alkaline cell (non-rechargeable) Lithium cells Silver oxide Zinc air cells Mercury battery Flow battery Fuel cell Lead acid Lithium ion Nickel cadmium Nickel metal hydride Lithium ion polymer Rechargeable alkaline battery (RAM) Nickel zinc Atomic battery Biological photovoltaic cells (algae) BPV Suggested Websites: Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

25 Student Decision Grid Grade Table for Internet Information BATTERY TYPE TABLE 1 Environment Criteria/Conditions of Focus (3) Source Address Supporting Data TABLE 2 Economics Criteria/Conditions of Focus (3) Source Address Supporting Data Science: Chemistry, Environmental Science, STEM 25

26 Lesson 1 Electrochemistry and Battery Sustainability TABLE 3 Social Equity Criteria/Conditions of Focus (3) Source Address Supporting Data Day 2 Directions: Complete the decision grid for each of the three criteria using the following scale: Rating Scale 3 Meets all or nearly all of the criterion 2 Meets most of the criterion 1 Meets some of the criterion 0 Meets little, if any of the criterion YOUR GROUP RESULTS 1 Plot your number rankings on the decision grid triangle for each criterion. 2 Use a ruler to connect your points together to make a triangle for your group within the decision grid triangle. 3 Shade or color your triangle. 26 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

27 Student Decision Grid Area of a triangle = ½ base x height 4 Calculate the area of the original decision grid triangle. Measure length using this unit: Side 1 = Side 2 = Side 3 = Original Decision Grid Triangle Area = 5 Calculate the area of your colored triangle. Side 1 = Side 2= Side 3= Your Shaded Triangle Decision Area = 6 What is the difference between the original decision grid triangle and your triangle? (Subtract areas to calculate answer.) Difference = Explain what this difference represents: CLASS RESULTS Complete the Table - 4 for the class rankings. 1 Which group (battery type) had the largest triangle area? 2 Why was their triangle the largest? 3 Which type of battery, according to the class results, is the most sustainable? Explain using the information presented. 4 How did your group rank in the battery types? Summarize this ranking based on the class information. Science: Chemistry, Environmental Science, STEM 27

28 Lesson 1 Electrochemistry and Battery Sustainability TABLE 4 Class Rankings TYPE OF BATTERY SOCIAL SCORE ENVIRONMENT SCORE ECONOMIC SCORE AREA OF TRIANGLE 28 Electrochemistry: Constructing a Battery and Deciding on a Sustainable Battery

29 Standard Reduction Potentials Grade Science: Chemistry, Environmental Science, STEM 29