Gases: They're Really There

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Objective

SWBAT identify properties of gases using video and a lab demonstration.

Big Idea

Through videos and a lab demo, students will investigate gases and the motion of their molecules.

Engage

5 minutes

Teacher Tip: This lesson addresses NGSS MS-PS-1 as students will draw models of the structure of molecules for gases in comparison to liquids and solids.  This lesson involves videos shown from The American Chemical Society's middle school science page.  The videos don't require sound, but you'll need something to show the videos and an internet connection. You will need materials for the elaborate section of the lesson, as well. For each table: an erlenmeyer flask, plastic wrap to cover the mouth of each flask, 2 buckets (one with hot water you've had boiling before class and one with cold water you've put a few ice cubes into).

To start this lesson, students will reflect on what they already know about gases will attempt to provide two examples of gases on their student notes sheet

After 3-4 minutes, I will ask students to share their responses, making a comprehensive list on the SMART board for all students to see. 

Explore

5 minutes

To begin an academic discussion about gas and matter, students consider the following prompt found in their notes sheet and then begin a conversation with their small groups or shoulder partners.

Decide with your group members, whether or not you think AIR is made of matter and how you know.

Students don't always think air is made of matter right away. They say things such as, "It's invisible" and/or "I can't see it, so it doesn't have matter." Ask them how they know air is there? Or, what it would be like with no air?

Explain

10 minutes

For this next section, you'll need a projector with internet connection to show the video demos to the class. I preview the questions by reading them aloud to the students prior to showing them the demo.  We watch the demo twice (important). Students answer questions while watching. 

DEMO #1

What is the mass of the deflated basketball?

What is the mass of the inflated basketball?

What does that tell you about air?

DEMO #2

What is the mass of the air can before using it?

What is the mass of the air can after using it?

What does this tell you about air?

I give them a few minutes after the second showing of the demo is finished to complete their responses. I then solicit 2-3 students to share their responses for the class. 

Elaborate

10 minutes

This next section involves distributing materials for students to see an actual demonstration first hand. You should have them prepared a head of time, and can ask students to help with the distribution. 

Guided Exploration

Students have an empty erlenmeyer flask with plastic wrap on the mouth and two containers of water, one hot and one cold. They place the flask into the cold water  - the wrap should sink down and become a depression. Students make observations and record them in their notes sheet, then do the same with the hot water  - the wrap expands and forms a small bubble. Again, they make observations and record them in their notes sheet.

Students use their notes sheet to guide their exploration with the demonstration: 

Each bottle, has a plastic film on the lid and air inside the bottle.

  1. Place the bottom of the bottle into the hot water.

  2. What do you observe?

  3. Why do you think this happens (think about the molecules)?

  4. Place the bottom of the bottle into the cold water.

  5. What do you observe?

  6. Why do you think this happens (think about the molecules)?

They should be discussing the motion of the molecules in questions 3 and 6, mentioning how the molecules are moving faster or slower, spreading out and getting closer together. 

Evaluate

5 minutes

The last bit of the lesson requires students to reflect individually on the demos and the task they've just completed by responding to the following prompt in the notes sheet: 

Using info from the video and lab demos, answer the following questions.

When we heat air molecules, what happens?

When we cool air molecules, what happens?

Predict what would happen to a balloon if you filled it up with air in a warm room and then brought it outside into the cold. Use evidence from the demonstrations.

For an example of a student response, see EVALUATE sample.  It shows a student's thinking with regards to the concept of molecules reacting to temperature.