Air Is a Mixture of Gases (t)

Activity-at-a-Glance

- Students discuss the composition of air.

- Students conduct experiments about the properties of air and the atmosphere, about the ability of air to take up space and has weight, and about how plants affect air composition.

Students consider two basic characteristics of air: it is a mixture of gases; it occupies space and has weight. This is important background for all students, but is of particular importance to those who will study the CO₂ strand.

Classroom Management and Preparation

The activity begins with a class-wide discussion, but students work in teams to conduct the three experiments (Step 2). In addition to the materials for the experiments, either you or students will need to assemble the TERC air pump. Instructions can be found with the TERC Air Pump.

Materials

Listed also in individual experiments:

Instant Clouds

clear glass bottle or flask,  250 ml to 4000 ml

single hole stopper to fit  the bottle

flexible tubing, at least 40 cm long

stiff tubing that forms airtight seal with the single-hole stopper (about 5 cm)

TERC air pump

Matches

Reaction in a Bag

sodium bicarbonate

(baking soda)

vinegar

small containers

sealable, clear plastic

bags

balance, if available

Recommended Procedures

1. Have students consider the composition of air.

The explorations introduce the composition of air and how biotic functions can change it. One way to begin this introductory discussionis with students’ own experience of air. Ask them to take a deep breath, hold it as long as possible, and then breathe out. Have student groups discuss differences between the air inhaled and the air exhaled. Other prompting questions include:

- Do you think that by breathing you are changing the air

around you?

- What do you think is in the air around you? Can you name

any of the specific gases in the air?

- What impact do you think plantshave on the composition of air?

2. Introduce and have students conduct several experiments.

1. Instant Cloud

2. Reaction in a Bag

Together these experiments will help students raise questions and make observations about the composition of air and how it occupies space and has weight. The experiments are described in the corresponding student materials. The teacher background sheets describe the scientific foundation for each experiment. You may share this sheet with students, or convey the information as the groups conduct their work.

Be sure students record their observations of their experiments in their GL Journals.