I Scream, You Scream...
Lesson 2 of 12
Objective: SWBAT differentiate between physical and chemical changes, investigate the effects of heat transfer on phase changes, and describe the concept of freezing point depression.
I start the lesson and spark student interest/curiosity with two demonstrations*.
Demonstration #1 - Making Rain:
Using a kettle with boiling water and a very cold ladle or large spoon that has been in the freezer for 1 hour, hold the cold spoon over the steam and students will see condensation droplets forming and dropping from the bottom of the spoon. Discuss water changing into steam (evaporation), then back to water again (condensation).
Demonstration #2 - Dry Ice Sublimation: Fill the classroom sink or large container with water and carefully place a piece of dry ice in the water. Place a regular piece of ice on a nearby counter or table. Carbon dioxide is heavier than air and so the students will observe the gas “spilling over” the side of the container and sinking to the floor.
Explain that dry ice, or frozen carbon dioxide (a solid), changes directly to a gas (carbon dioxide that we breathe out). This is called sublimation. Unlike the ice on the counter, which changes first to a liquid phase (water) and then upon heating changes to a gas (water vapor), frozen carbon dioxide bypasses the liquid phase. A chunk of dry ice can also be carefully placed in a rubber glove or balloon and sealed it with an elastic band. Students can watch the balloon expand as the dry ice changes into a gas. Be sure to remove the dry ice or poke a hole in the glove/balloon before it bursts.
After the demonstrations are completed, I ask the students how matter can change from one state to another, and select volunteers to respond.
Demonstrations adapted from www.scientistinresidence.ca.
The bulk of this section serves to build the necessary background knowledge students will need in order to move on to more advanced concepts presented in the lab. I start by passing out the Ice Cream Lab guide and have students read the introduction with a partner. This gives them an understanding of the process and expectations for the day's activity. Be sure to check in on their understanding after they've finished reading. You could do that by having them explain their reading to another partnership, or whole class.
Next, I want the students to gain some clarification about the molecular activity that takes place in each state of matter. In order to do this, I have them access the following animations, writing notes in the appropriate section of their lab as they watch:
Now that students have developed an understanding of the phases of matter and how they work on a molecular level, I want them to know the correct terminology for each phase change. I have the students access the following Change of States graphic and use it to complete some of the definitions on the lab guide before starting the lab.
We are now at the point where all of the background knowledge has been built, so it is time for the students to understand the lab procedures. I have the students watch the first 3 minutes and 10 seconds ONLY of the Sci Guys 10 Minute Ice Cream video. (The remainder of the video will be shown after the lab - see "Elaborate".)
After viewing the video, I ask a few simple recall questions about the process to make sure students understand the process of making their ice cream. I direct them to the "Materials" and "Procedures" sections of their lab guide to refer to as they perform the lab.
Next, it is time to make some ice cream! I have one Materials Manager from each table group gather the necessary materials for their table and allow the students to follow the directions from the video, as well as listed on their lab guide.
*Before serving the ice cream to students, ensure that no student is allergic to vanilla or is lactose intolerant.
Now that we have conducted the lab, the students get to eat their ice cream! Unfortunately, they also have to clean up. If I allow them to do both together, the clean-up part is usually accompanied with fewer groans of reluctance.
Next, it is time to learn the science behind this phenomenon. We watch the remaining 2 minutes of the 10 Minute Ice Cream video (from 3:10-5:18), in which the Science Guys explain how the ice cream is made.
In addition to watching the video, students buddy read the "What happened?" section of their lab, stopping at the end of each paragraph to summarize, paraphrase, and ask questions about what they just read.
We then discuss as a class - I call on random students to summarize each paragraph and we answer each others' questions from the buddy read. Here it is critical to hold out for complete and correct responses.
Now that students have built background knowledge about physical changes, state of matter, and freezing point depression, it is time to see how much they have actually learned and how deeply they can analyze/apply the information they have learned.
I assess student knowledge by having them complete the vocabulary chart and the reflection questions on their lab. The questions in the lab range from basic understanding to creating a model to illustrate freezing point depression. Not only does it give me an idea as to their understanding of physical changes and states of matter, but it also helps me to gauge how well they can break the processes involved in the lab into smaller more "digestible"parts, which requires a great deal of higher order thinking on their part. This can be done in class, as a homework assignment to accompany the lesson, or as a way to begin the next day's class and as a guide to a class discussion.