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Investigating Air
BO RA
T
Students explore the nature of air by making observations on air pressure and on the
interaction of air and a chemical indicator. This gives them direct evidence that,
although air can be invisible in their everyday experience, it is made up of gases that
have distinct properties.
KEY CONCEPTS AND PROCESS SKILLS
(with correlation to NSE 5–8 Content Standards)
1.
“Air” is an everyday term that refers to the atmosphere at the earth’s surface. The
atmosphere has different properties at different elevations and is divided into
layers. (EarthSci: 1)
2.
The atmosphere is a mixture of nitrogen, oxygen, and trace gases that include
water vapor. (EarthSci: 1)
KEY VOCABULARY
air
substance
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Activity 63 • Investigating Air
MATERIALS AND ADVANCE PREPARATION
For the teacher
1
Transparency 63.1 , “Composition of Air”
*
1
transparency of Student Sheet 63.2 , “Air Investigations”
*
1
overhead projector
1
Scoring Guide: UNDERSTANDING CONCEPTS (UC)
For each group of four students
1
bottle of BTB (bromthymol blue) indicator
1
cup of water
For each pair of students
1
plastic syringe
1
SEPUP tray
1
stir stick
For each student
*
1
Student Sheet 50.2, “Scientific Careers in Weather”
1
pair of safety goggles
1
Student Sheet 63.1, “Anticipation Guide: Air”
1
Student Sheet 63.2, “Air Investigations”
1
Scoring Guide: UNDERSTANDING CONCEPTS (UC) (optional)
*Not supplied in kit
Bromthymol blue (BTB) is an acid-base indicator that is blue in basic solutions and
yellow in acidic solutions. In this activity, it is important that the BTB solution that
acts is the control be blue; only then is a solution containing excess dissolved carbon
dioxide obviously yellow in contrast. If you are in an area with extremely soft water
(in which the addition of the bromthymol blue results in a yellow-green color rather
than a blue color), use distilled water instead of tap water.
Masters for Scoring Guides are in Teacher Resources III: Assessment.
SAFETY
Always handle chemicals carefully, and wear safety goggles. Instruct students to wash
their hands after completing the activity.
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Investigating Air • Activity 63
TEACHING SUMMARY
Getting Started
1.
(LITERACY) Use Student Sheet 63.1 to elicit students’ preconceptions about air.
Doing the Activity
2.
Students investigate some properties of air.
Follow-Up
3.
(UC ASSESSMENT) Students are introduced to the idea that air is a mixture of
gases.if this works)
BACKGROUND INFORMATION
Indicators
Bromthymol blue (BTB) is a chemical indicator that is yellow in acidic solutions and
blue in basic solutions. Its equivalence point is at pH = 6.7; consequently, it is blue in a
neutral solution (pH = 7). As a solution of BTB gradually changes color, it appears to
go through an intermediate green stage. The green color results from some of the BTB
molecules being in the blue state and some in the yellow state. Since carbon dioxide in
solution produces carbonic acid, BTB is yellow in the presence of sufficient carbon
dioxide. Addition of enough base (such as sodium hydroxide) to a yellow BTB solution
will eventually turn the solution blue, as the base first neutralizes the acid and then
turns the overall solution basic.
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Activity 63 • Investigating Air
TEACHING SUGGESTIONS
GETTING STARTED
1.
(LITERACY) Use Student Sheet 63.1 to elicit
students’ preconceptions about air.
Student Sheet 63.1, “Anticipation Guide: Air,” provides a preview of important ideas in the activity
and an opportunity for students to explore conflicting ideas they may have about the material. Hand
out Student Sheet 63.1. You might read the statements aloud, and clarify any questions students
might have about their meaning. Instruct each students to record whether they agree or disagree with
each statement by placing a “+” or “—” in the Before
column. Explain that they will have a chance to
revisit these statements after the activity to see if
their ideas have changed or remained the same.
Read the Challenge aloud and ask several students
to discuss their ideas and describe evidence to support them. Note that the word substance, which
can be defined as anything that has mass and occupies space, is not used in a formal scientific way. The
Challenge question can be reframed to ask, “Can
you prove that air is something as opposed to nothing?” Explain that this investigation will supply
some evidence to help answer the Challenge and
address the statements in the anticipation guide.
DOING THE ACTIVIT Y
2.
Students investigate some properties of air.
Before you distribute the materials, remind students of the proper use of lab equipment, particularly the syringe. Emphasize that when removing
the plunger, it is important they do it firmly and
gently so they will not damage the rubber tip. You
may want to demonstrate how to do Procedure
Steps 14 and 15.
Distribute the materials, including Student Sheet
63.2, “Air Investigations,” and have students work
in pairs to complete Procedure Parts A and B. In Part
B, students collect evidence about air by using
bromthymol blue (BTB) as an indicator for carbon
dioxide.
■ Teacher’s Note: BTB is actually an acid-base
indicator that is blue in basic solutions and yellow
in acidic solutions, such as those containing dissolved carbon dioxide. Because students may not be
familiar with acid-base chemistry, which is not
essential to this activity, the distinction is not
addressed in the student materials.
Sample Response to Student Sheet 63.2, “Air Investigations”
Table A: What is Air?
Table B: Is Air Always the Same?
Observations
Observing air
Colorless, odorless, transparent
Air on my arm
Feel a soft wind, moves some
hairs on my arm
Holding the
tip tightly
Very hard to press down, lots of
resistance
Holding and
releasing
the tip
First hard to press down, but
then easy after tip is
released; air blows out in a puff
after release
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Initial Color
Final Color
Control
(Cup A)
Clear bright
blue
Clear bright
blue
Classroom
air (Cup B)
Clear bright
blue
Clear bright
blue
Air from
lungs
(Cup C)
Clear bright
blue
Lighter blue,
green, or yellow
Investigating Air • Activity 63
FOLLOW-UP
3.
(UC ASSESSMENT) Students are introduced to
the idea that air is a mixture of gases.
When all groups have finished their investigation,
project a transparency of Student Sheet 63.2, and
use it to compile students’ observations. Encourage
every student to contribute an observation. Discuss
similarities and differences in their observations
and lab results.
Use Analysis Question 1 to revisit Student Sheet
63.1. Allow students a few minutes to respond to the
statements on the student sheet.
Review students’ responses to Student Sheet 63.1,
and introduce the idea that air is a mixture of gases.
Ask, What evidence do you have that air is a gas? Evi-
the classroom air was not enough to change the
BTB color.
At this point, refer students to Student Sheet 50.2,
“Scientific Careers in Weather.” They should look at
the skills for the scientific career they choose to
focus on, and mark those that they have mastered.
If they need to, they should look through their notebook and the student book to refresh their memory.
Analysis Question 4 provides an opportunity to
assess students on their ability to understand concepts. If you plan to use the UNDERSTANDING CONCEPTS
Scoring Guide to score their answers, review your
expectations for a complete and correct response
(for example, citing at least three pieces of evidence).
SUGGESTED ANSWERS TO QUESTIONS
dence includes the “wind” that could be felt on an
arm and the pressure that was felt when pressing
1.
Use your laboratory results to discuss the
following questions:
an “empty” syringe. Ask, How do you know that air
is not always the same, that is, not a single gas? The
classroom air and the exhaled air did not affect the
indicator in the same way; only the exhaled air
changed the color of the BTB solution. The fact that
billions of people on earth are breathing in and out
means that a lot of the gas that changed the BTB
color is in the air, even though the concentration in
a. How can you describe air?
Air is something that can be felt when it
blows and that can be hard to compress.
b. Is air always the same?
No, air is not always the same. For example,
classroom air and the air exhaled by a person are different.
Final Responses to Student Sheet 63.1, “Anticipation Guide: Air”
—
1. Air is made up of nothing.
This statement is a false statement that students should disagree with by the end of the activity.
Air is made up of a mixture of gases. (Evidence for this is described in Teaching Suggestions Step 3.)
+
2. It can be hard to compress the air in a small container, such as a plastic syringe.
This statement is true and should be supported by the work that students did in Procedure Part A,
in which gases tend to exert increasing pressure as they are compressed into a smaller and
smaller volume.
—
3. The air that I breathe out is the same as the air that I breathe in.
This statement is false. Students should have evidence of this from Procedure Part B, which
demonstrated that exhaled breath contains higher levels of carbon dioxide. Transparency 63.1,
“Composition of Air,” summarizes these differences.
+
4. Wind is the movement of air.
This statement is true. Some students may be able to relate air to wind, based on their experience
in Part A.
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Activity 63 • Investigating Air
c. Look again at Student Sheet 63.1. Would you
change any of your answers? How?
Students are likely to change some of their
answers. A complete response to each statement on Student Sheet 63.1 is in Teaching
Suggestions Step 3.
2.
Do your observations from Part A provide
evidence that air is a substance? Why or
why not?
Yes, they provide evidence because you can feel
the air that is pushed out of the syringe and onto
your skin. You can also observe how hard it is to
push down on a plugged syringe. Both of these
observations indicate that air is something
inside the syringe that can be pushed out, or
when trapped inside, exerts resistance.
3. Look at your results from Part B. Is the air that comes
out of your lungs the same as your classroom air?
Explain.
No. Although both kinds of air made bubbles in
the water, the classroom air did not change the
color of the indicator and the exhaled air did.
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4.
(UC ASSESSMENT) Is air a substance or is it just
empty space? Support your answer with evidence
from this investigation.
Students should conclude that air is a substance
and should support their conclusion with evidence similar to that provided in Analysis Questions 1 and 2. An example of a Level-3 response
is shown below. A Level-4 response might refer to
air as a mixture of gases or describe the relationship between humans breathing air in and out
and air’s composition.
Level 3 Response:
Air is a substance because you can feel it blow
out of the syringe, just like when the wind blows.
If air were empty space, it would not be able to
keep you from pushing the syringe down when
the end was plugged. It would not change the
BTB color either.
Composition of Air
Inhaled Air
Exhaled Air
Nitrogen
78%
78%
Oxygen
21%
16%
0.04%
4%
Water vapor and
other trace gases
1%
2%
©2006 The Regents of the University of California
Carbon dioxide
Issues and Earth Science • Transparency 63.1
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Name
Date
Anticipation Guide: Air
Before starting the activity, mark whether you agree (+) or disagree (—) with each
statement below.
After completing the activity, mark whether you agree (+) or disagree (—) with each
statement below. Under each statement, explain how the activity gave evidence to
support or change your ideas.
Before
After
1. Air is made up of nothing.
2. It can be hard to compress the air in a small container,
such as a plastic syringe.
3. The air that I breathe out is the same as the air that I
©2006 The Regents of the University of California
breathe in.
4. Wind is the movement of air.
Issues and Earth Science • Student Sheet 63.1
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Name
Date
Air Investigations
Table A: What is Air?
Observations
Observing air
Air on my arm
Holding the tip
tightly
Holding and
releasing the tip
Table B: Is Air Always the Same?
©2006 The Regents of the University of California
Initial Color
Final Color
Control (Cup A)
Classroom air (Cup B)
Air from lungs (Cup C)
Issues and Earth Science • Student Sheet 63.2
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