Engineering Design Challenge: Building a Voltaic Cell in the High School Chemistry Classroom

ILLUSTRATION OMITTED The number of students majoring in science, technology, engineering, and math (STEM) is declining due in part y to a lack of student interest (Fairweather 2008; NRC 2012; PCAST 2010). One reason may be the difference between how science is done in school and how it's done in the field (Osborne, Simon, and Collins 2003). An interdisciplinary approach that incorporates engineering design with the practical applications of science, however, may help spark student interest in STEM subjects. This article describes an engineering design challenge in which students design and build an electrochemical (voltaic) cell with a motor and fan to help them observe the cell's energy production. Background We teach this activity in a chemistry class, but it is cross-disciplinary in nature and addresses current science standards (Figure 1). To focus on the engineering design aspect of this challenge (see sidebar, p. 35), we recommend using it as the culminating activity to an electrochemistry unit. Before starting the activity, students should be familiar with such terms as cathode and anode, be able to complete relevant calculations, and have appropriate laboratory skills (Figure 2, p. 32). Many high school chemistry courses may not cover electrochemistry in depth, but this activity can be made appropriate for a unit on chemical reactions by adding more teacher direction on how to create an electrochemical cell. For example, teachers can provide students with the structure of an electrochemical cell and a list of half-cell potentials for only the metals available to make the activity accessible for students with limited knowledge of electrochemistry. The design challenge The engineering design challenge typically takes two 90-minute class periods to complete. We begin by giving groups of two to four students a list of available materials and design requirements (Figure 3). This is similar to authentic engineering design, which is driven by specifications and constraints (see sidebar). We purchase the motors, alligator clamps, voltmeters, metals, and solid metal nitrates needed for this activity from a chemical supply company. Silver-based products such as Ag(s) and AgNO.sub.3(aq) can be expensive, but they increase the variety of possible designs; other metals and metal salts can be used instead. Metal nitrate solutions can be used if solid metal nitrates are prohibited. With the necessary materials and instructions, student groups engage in the engineering design process of planning, designing, testing, and evaluating their voltaic cells and fans (Figure 4, p. 34). Teachers can format a structured design log for students--or allow students to create their own--based on these steps. Let's look at each stage in more detail. Planning: Brainstorming and research Students brainstorm how they might create a voltaic cell and conduct research to inform their design. We recommend having the materials (Figure 3) available to them during this part of the process so they can explore how the motor works and visualize the size of the cell's porous cups. Students may want to use the battery to see how electrical energy is converted to mechanical energy, for example, or feel the different materials available for their fans. While students are coming up with ideas for how they might approach the problem, we can formatively assess their understanding of electrochemistry. After this initial brainstorming session, students conduct research to determine how they might build a voltaic cell. During this phase of the planning, they write their questions in their design log and research the answers. For example, they might wonder how to determine which metals or salts will produce energy. Through research, they find that a positive cell potential from two half-cell reactions will produce energy, and that certain combinations produce more potential electrical energy than others. …