GISAT 112 Lab
EXPLORING GAS BEHAVIOR
There are three parts to this lab. Their objectives are:
A. Measuring a breath of air: design and conduct an experiment using simple equipment to
obtain an estimate of an environmental parameter (the typical volume of air breathed by
an adult human in a 24-hour period).
B. Weighing air and graphing data: conduct a simple laboratory experiment (mass of air vs.
pressure in a constant-volume container) and plot the data, using good graphing
techniques.
C. Investigating ideal gas behavior: develop a hypothesis regarding ideal gas behavior,
design and conduct an experiment to test this hypothesis, and then evaluate the
experiment for possible sources of error.
A. MEASURING A BREATH OF AIR
[Adapted from Chemistry in Context, 4th Edition, 1.1 Consider This: Taking a Breath]
In this portion of the lab you will design and execute simple experiments to estimate the
volume of air you inhale in a typical day. You will measure how much air you inhale in a
typical breath and how many breaths you typically take in a minute, and then estimate how
much air you inhale in a day (24 hours).
Work in teams of 3-4 students. You may use any of the equipment available in the lab. You
may find it helpful to complete the work sheet below (or in a lab notebook), to record and
organize information that will be in your write-up for this lab.
Names of Team Members:
1. Describe your experimental design:
2. Determine how many breaths you take in a typical minute and record the answer here:
3. Record the measured volume of air you breathed in a typical breath:
4. Using your answers to steps 2 and 3, estimate how much air you inhale in 24 hours:
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GISAT 112 Lab
Questions to be Discussed in Lab Report (see “Reporting Requirement”, page 5)
1. What factors (variables) could have affected your answers to steps 2 and 3?
2. The inhaled volume/day that you determined experimentally may not fall into the typical
range given by your instructor. Discuss the 2 or 3 most likely sources of error in your
experiment.
B. WEIGHING AIR AND GRAPHING DATA
[Adapted from Chemistry in Context Laboratory Manual, 4th edition]
Introduction
Graphs provide an important and very useful way to present data in most disciplines. Graphs
summarize the numerical data efficiently and are usually easier to understand and interpret
than columns of numbers. Graphs are used frequently in your Chemistry in Context textbook.
In this assignment, you will collect some experimental data that lends itself to presentation in
graphical form. You will then learn how to construct graphs in ways to make the visual
presentations most effective. [Refer to the section on graphing data at the end of this lab
description.]
Overview of the Experiment
1. Pump air into a 2-liter bottle to about 40 pounds per square inch pressure.
2. Weigh the bottle and measure the pressure in the bottle. Record your data.
3. Release some of the air; measure the pressure and weigh the bottle again. Record
your data.
4. Repeat step 3 several times until all of the air pressure has been released, recording
your data after each step.
5. Graph the data (this is also referred to as “plotting” the data). Use a pencil for this
step, because it is easy to make mistakes. Make small dots, and then draw small
circles around them so that they show up clearly.
6. Using a straight edge (preferably transparent), draw the “best” straight line through
the data points. This step requires some judgement. If the points are somewhat
scattered, there should be equal numbers of them on either side of the line.
7. If specified by your instructor, calculate the slope of the line. To do this accurately,
select two points on the line near the ends of the line. Carefully read off the x and y
values for each. If you are unsure how to calculate the slope, refer to the
“background” section on graphing at the end of this lab description.
Materials
1.
2.
3.
4.
2-liter plastic soda bottle with a tire valve in the cap
Tire pressure gauge
Hand bicycle pump
Pan balance with 0.01 g accuracy
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GISAT 112 Lab
Experimental Procedure
1. Your instructor will explain use of the balances in your laboratory. When using an
electronic-type balance, it is important to make sure the balance reads zero when
empty (usually accomplished by pressing a “zero” or “tare” button). It is a good idea
to recheck the zero each time you use the balance. For this experiment, you will need
to make measurements to the nearest 1/100 of a gram (0.01 g). If your scale is more
sensitive (0.001 g), record all digits.
2. Make sure the cap is tightly on the bottle, and then pump some air into it with the
bicycle pump (do not exceed 40 psi). Have each member of the team practice using
the pressure gauge. You need to be able to push the gauge on squarely without letting
out much air, and you need to know how to read the pressure units. The pressure scale
will probably be marked in pounds per square inch (“psi”). *
3. Pump up the pressure in the bottle to about 40 psi.
4. Weigh the bottle and record the mass to the nearest 0.01 gram.
5. Wait 5 minutes and re-weigh the bottle. If the mass has not changed, the cap is sealed
tightly and the experiment can be started. If the mass has decreased by more than 0.05
g from the reading in step 4, tighten the cap and repeat steps 3-5.
6. With the bottle at about 40 psi, let a small amount of air out of the bottle. Measure
and record the pressure again, then re-weigh and record the mass.
7. Repeat step 6 until you have obtained at least five sets of pressures and masses
between your highest reading and 10 psi.
8. Let all of the air out (so that the gauge pressure is 0) and re-weigh. (Of course, the
bottle is not really empty. It now has the same air pressure as the surrounding air, or
about 14.7 psi.)
9. Optional: If time permits and you are interested, you might repeat the study. (In
scientific studies, the measurement technique often improves with repeated
experiments.)
* Note: the gauge is measuring pressure above the current atmospheric pressure. This is
referred to as “gauge pressure”. Absolute pressure, as used in the Ideal Gas Law, is the
sum of atmospheric pressure and gauge pressure.
Questions to be Discussed in the Lab Report
1. For the graph of mass versus pressure, which do you think was more reliable, the data for
the mass or the data for the pressure? Explain you answer. Make a general estimate of the
probable uncertainties in each of your mass and pressure measurements. To do this, think
about the measuring device and how you used it.
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GISAT 112 Lab
C. INVESTIGATING IDEAL GAS BEHAVIOR
In this part of the lab you will investigate relationships between two properties of a gas.
Gases are unique among forms of matter in that their behavior can be generalized. The
relationship between variables such as temperature, pressure, volume, and number of
molecules (or “moles”) is almost the same no matter which gas you are measuring.
Most gases in the environment behave according to the Ideal Gas Law: PV = nRT
Where P = absolute pressure (e.g., in atmospheres)
V = volume (e.g., in liters)
n = amount of gas (in moles)
R = the universal gas constant (in units consistent with the units of P, V, n, and T)
[e.g., R = 0.082 L·atm/K·mole]
T = absolute temperature (e.g., K)
This law has direct application to your experiments in this lab. For example, for a given
amount of gas (constant n) in a container held at a specific temperature (constant T):
nRT = constant, so
PV = constant.
Therefore, if P is changed from P1 to P2, V must change so that:
P1V1 = P2V2 at fixed n, T (History note: this is a statement of Boyle’s Law)
Similarly, if P and n are constant, V/T = constant, so:
V1/T1 = V2/T2 at fixed n, P
(Charles’ Law)
Finally, if V and n are constant, P/T = constant, so:
P1/T1 = P2/T2 at fixed n, V
(Gay-Lussac’s Law)
There are several such relationships that could be investigated in this lab. You will need to
select one of them in step 1 of the method described below.
You and your teammates are to investigate the relationship between two of the following
variables: pressure, volume, or temperature for a gas of your choice. You must design an
experiment to study the relationship, obtain data for at least 3 values of the independent
variable, and describe your investigations and results in your lab write-up. One hint to get
you started: Since these variables are interrelated, it is important to control the variables you
are not studying!
Materials: You may use anything your instructor provides that you feel will help you solve
the problem. A partial list of possibilities:
Thermometer
Balloons
Rubber bands
Plastic food storage bags
Ziploc food storage bags
Straws
Graduated cylinders
Pressure gauge
Dishpans
Rubber tubing
Meter stick
Glass tubing
Two-liter plastic bottles with valve stems
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GISAT 112 Lab
Experimental Procedure: Work in teams of 3 - 4 students.
1. Identify the relationship you will investigate. Before going any further, you should make
a hypothesis about the type of model you expect to find: linear, exponential, etc. The
hypothesis should be stated as a simple declarative sentence such as: "There is a linear
positive relationship between the mass of a gas and the pressure it exerts in a closed
system."
2. Develop a plan for testing your hypothesis. On the worksheet provided, describe the
experimental design in enough detail that another team of students could follow it.
Explain how the factors you are not studying will be controlled.
3. Carry out the plan. Gather all data that you consider necessary to answering your
question. Keep a record of all the data you collect. Keep in mind that the best results
require repetition. You should try to repeat your measurements at least twice (i.e., make
three sets of measurements). A blank data table is provided for recording your
measurements, but use another format if you prefer. Be sure to enter the units of your
measurements, and note which variables were held constant. Blank graph paper is also
provided, for plotting your results.
Questions to be Discussed in the Lab Report
1. State the two variables you chose to investigate, your hypothesis about the relationship
between them, and describe your experimental design. Do your data support your
hypothesis?
2. Discuss the 2-3 most likely sources of error in your experiment.
3. Extra credit: Plot your data with Excel, select a trend line curve to represent your data,
show the correlation coefficient (R2) on the plot, and discuss how well your data fit the
curve, based on the value of R2.
Reporting Requirement
After class, prepare a report as a Word document (attach the Excel plot if you do the extra
credit). This report will not be considered a full lab report, so it is not necessary to follow the
guidelines for laboratory reports. The report should show the names of team members and
the title of the lab, followed by a section on Measuring a Breath of Air, a section on
Weighing Air and Graphing, and a section on Investigating Ideal Gas Behavior. Each of
these sections should include at least one paragraph on experimental approach (or design),
data obtained (or results), and discussion. Submit either a hard (paper) copy, or an electronic
file via the Blackboard digital drop box (your instructor will advise). This report is due by the
beginning of next week’s lab.
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GISAT 112 Lab
Investigating Ideal Gas Behavior
Experimental Design:
Run
No.
Pressure
(
Volume
)
(
)
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Temperature
(C)
Notes
GISAT 112 Lab
Exploring Gas Behavior
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