Academic journal article Science Scope

Message in a Bottle: Analyzing Reaction Rates Using Gas Pressure Sensors

Academic journal article Science Scope

Message in a Bottle: Analyzing Reaction Rates Using Gas Pressure Sensors

Article excerpt

One of the many ways to engage students in science is by using probes or computerized devices that respond in real time to changes. By using devices such as motion sensors, temperature probes, and pressure sensors, we found that students not only appear to enjoy science more, they also seem to ask more questions (many times with unbridled enthusiasm!). In addition, students think more deeply about what is causing the changes sensed by the probe or what they could do to generate different results from the probe.

In the following learning cycle lesson, an after-school science and mathematics club consisting of about 20 students uses a computerized pressure sensor. This type of sensor is available from laboratory supply companies. You will need one sensor for every three to four students. You will also need to interface each sensor with a computer or other device (Vernier's LabQuest, PASCO's SPARK, etc.) to evaluate the rates at which effervescent tablets (such as Alka-Seltzer) dissolve. Students then apply that knowledge to working with effervescent rockets. In all, the lesson takes about one and a half to two hours, which could easily be completed within three or four days in the classroom.

Before you begin this activity, students should be familiar with physical and chemical changes as well as have a rudimentary understanding of pressure. It is also helpful if they are comfortable working with computerized sensors and creating graphs. This activity can be used as an introduction to chemical changes/reactions, as part of a unit on chemical versus physical changes, or as part of a unit on graphing independent/dependent variables.

Safety

As with any experiment involving pressure, all students in the lab (not just those actively participating in an experiment) must be wearing impact-resistant safety goggles. Because this activity uses chemicals, goggles with splash guards are ideal. The sealed bottles and rockets must not be pointed at any person or at anything breakable.

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Engage

To familiarize students with how the gas pressure sensors work, we first connected one to an empty 0.5 L plastic soda bottle, and several volunteers squeezed the sealed bottle for 30 seconds each. As students squeezed, they were excited to see the real-time change in pressure that was being graphed on the computer projection screen (see Figure 1). We challenged students to grip the bottle as hard as possible, at times allowing certain volunteers to use both hands (this "gripping" activity is from Let's Go: Elementary Science [Moore et al. 2005]). Virtually every student was eager and excited to give the bottle a squeeze.

As teachers, we made sure to constantly reference the graph being created as students squeezed, asking questions such as, "What does the x-axis represent?" "What does the y-axis represent?" "Why did the line go up so quickly here?" and "Why do most of the lines seem to gradually decline?" This gave students time to discuss their ideas as well as time for teachers to hear students' thinking. Although we only allowed 15 minutes for this stage, we could have extended it with variations on the ways students squeezed the bottle (e.g., left hand versus right hand, squeezing a tennis ball for 30 seconds before squeezing the bottle).

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At the conclusion of this short activity, we asked students what they thought would happen if we added water and an effervescent tablet to the sealed bottle. Some students predicted the bottle would explode; others thought the line on the graph would go up, indicating increasing pressure. As a demonstration, the authors placed one-quarter of a tablet into the bottle and sealed the top with a two-hole rubber stopper that came with the sensor. (The sensor is inserted into one hole and the other is used to add water to the system.) The authors then used a syringe to insert 20 mL of water (see Figure 2). …

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