Lesson Plan Template: Predict-Observe-Explain
Learning Objectives: What will students know and be able to do as a result of this lesson?
- Students will be able to define the Kinetic Molecular Theory.
- Students will be able to define Boyle's Law.
- Students will be able to describe the relationship between the pressure and volume of gases as it relates to the Kinetic Molecular Theory while temperature remains constant.
- Students will be able to create and interpret graphs relating the pressure and volume of a gas while temperature.
Prior Knowledge: What prior knowledge should students have for this lesson?
Students should understand that gas pressure is caused by the collision of gas particles against a surface.
Students should know that the greater the number of gas particles in a container, the greater the number of collisions that will occur, and the greater the gas pressure will be.
Prior knowledge will be activated in small group discussions. The teacher will present the groups with questions that they will discuss as small groups and then share their thoughts in a whole class discussion after they have had time (about 5 - 10 minutes) to come to an agreement.
Guiding Questions: What are the guiding questions for this lesson?
How can the Kinetic Molecular Theory be used to explain the relationship that exists between the pressure and volume of a gas as described by Boyle's Law?
Predict: What event, related to the focus topic, that may surprise students, will the students make a prediction about?
Students will have to predict what will happen to 4 different objects (a partially inflated balloon, a marshmallow, a cotton ball, and a penny) when the gas pressure around them is first decreased and then brought back to normal when placed in a bell jar.
*Please note that a separate Boyles_Law_Bell_Jar_POEs.docx will be completed for each item before beginning a POE on the next item, and that the POEs will be completed in the order listed for the objects above.
- Many students will predict that the balloon will decrease in size when using the syringe and then return to normal after the valve is released. They will find that the balloon increases because the syringe causes a decrease in the pressure around the balloon when it is in the bell jar. Some students will predict that the balloon will float in the bell jar. If they do, remember to discuss the concepts of gravity and air density during the class discussion after all experiments are completed.
- After seeing what happens to the balloon, the students will usually predict that the marshmallow will react the same way. The marshmallow will expand when the syringe is used, but they are very surprised (and excited) to see that it actually shrinks from its original size when the valve is released. The teacher should then ask them why they think this happened. What makes the marshmallow so different from the balloon? Hopefully they will come up with the idea that the gas molecules in the balloons are large enough that they will not effuse through the latex, but that the gas molecules in the marshmallow actually escaped, causing the marshmallow to collapse back in on itself when the pressure increased from the valve being released. If they repeat the process with the marshmallow it will continue to expand and then shrink to smaller and smaller sizes each time. (Many of my students like to take videos and pictures of the marshmallows).
- After seeing the results with the marshmallows, many students will predict that the cotton ball will also increase in volume when the syringe is used and "shrink" after the valve is released. They are very surprised when the cotton ball remains the same throughout the experiment, not increasing or decreasing at all. They should realize after this that the cotton ball does not contain trapped gases like the balloon and marshmallow. Many students will expect the cotton ball to float. If this happens, once again, include it in the class discussion to follow. Note: many times the cotton ball will move when the valve is released. In the discussion later the teacher will want to talk about the air movement caused by the opening of the valve.
- The penny usually doesn't surprise them much. At this point most students have figured out that there are no trapped gases in the penny and that the atoms that make up the penny have very strong attractions to each other and will therefore not increase or decrease in volume. Some students may still be surprised that nothing happens. If so, then share in their excitement!
Observe: What will the students observe and/or infer during this step of the lesson? How will students communicate their observations and inferences?
*Always follow lab safety procedures when working with students in the lab. Review these requirements before the lab.
The students will place the objects, individually and one at a time (in order) in a bell jar. They will remove air from the bell jar (decreasing the pressure) and observe what happens to each object. These observations will be written on their POE sheet. Then they will open the valve to return the pressure to normal and again observe what happens to each object. These observations will also be written on their POE sheet (they may include drawings if they prefer).
*The teacher should only have the bell jar apparatus, tubing, and syringe at the lab station to begin the lab. A bell jar apparatus set-up and explanation can be found in various scientific supply catalogs.
After students have completed the exercise that teaches them how the bell jar and syringe work, then the teacher will hold up a partially inflated balloon and ask the students what they think will happen to the volume of the balloon if it is placed in the bell jar and the syringe is used to remove the air. The teacher should then circulate to make sure the students are writing their predictions on the POE sheet. Once every student has committed to a prediction, then the teacher should pass out a balloon to each group so they may complete the experiment, make their observations, and then develop an explanation. After the balloons are collected, then the teacher should repeat the process with the three remaining objects, in order, one at a time.
Explain: How will students be encouraged to develop explanations using their observations and scientific or mathematical concepts or principles?
The teacher will circulate and ask students why they think they got the results that they did. As the students verbalize their ideas, the teacher may want to ask other questions of the students relating to their knowledge of gas pressure and kinetic molecular theory. The teacher will answer all questions with another question and then instruct students to write down their best explanation on their POE sheet.
After all POE sheets are completed, the teacher will lead a discussion about Boyle's Law using Boyles_Law_Notes.pptx, relating it to the Kinetic Molecular Theory. After the discussion is finished, students will return to their POE sheets and complete the Re-POE section for each object, giving a revised explanation for their observations.
POE sheets will be collected after the review on the second day and graded based on the Boyles_Law_Bell_Jar_POE_rubric.docx.
The students will be in groups of three or four. The teacher will need to circulate throughout the groups during the entire exercise asking questions of the students relating to their predictions and observations. Most of the information that the teacher gathers may be used during the discussion later, like certain misconceptions that arise, but sometimes there may be questions that arise that will need to be discussed immediately with the entire class to make sure that the students know what they need to do (how to correctly use the equipment, procedural information, etc).
The teacher should have students show (or explain) what their predictions are before giving the supplies necessary to make their observations.
Feedback to Students
Students will receive feedback during the teacher-led class discussion after the Predict-Observe-Explain activities (POEs) have been completed. Misconceptions will be covered as well as any other questions that may have arisen during the formative assessment.
After the discussion is completed, students will be given the opportunity to return to their POE sheets and revise their explanations (re-POE) based on the information gained in the class discussion.
Students will be given an exit slip at the end of class. They will be able to write down new concepts that they have learned and ask questions that they may still have. The teacher will review the Exit_Slip.docx to prepare a quick review for the beginning of the next class period.