Developing Our Ideas
Activity 5: A Massive Decision
Unit 4
Cycle 1
P ur p o s e
All the interactions you have investigated so far have involved solids and
liquids. But some interactions also involve gases. For example, party balloons
are sometimes filled with helium gas. Some appliances for the home, like hot
water heaters, furnaces and kitchen stoves, burn methane gas. Firemen wear
gas masks to keep from breathing the carbon dioxide gas produced when
wood and other things burn.
In this activity, the interactions you will study involve gases, including air.
Because we are interested in determining whether the total mass stays the
same or changes during these interactions, we have to know whether the gas
has any mass itself. The key question for this activity is:
Do gases have mass?
We Think . . .
Discuss the question below with your team and write your answer.
Do you think that gases have mass? Include your reasoning.
Participate in a class discussion about your answers.
Explore Your Ideas
Your team will do two experiments. In Experiment 1, you will put air into a
system by pumping up a soccer ball. In Experiment 2, you will remove the
gas produced by mixing vinegar and baking soda from a plastic bag system.
©2003 CIPS Project
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Unit 4 Cycle 1
Experiment 1: Putting Air into a System (Soccer Ball)
Suppose you measure the mass of a soft soccer ball, and then pump air into
the ball until the ball is firm.
1. What do you think will happen to the mass of the ball? Why?
Participate in a class discussion of your prediction and reason.
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Activity 5: A Massive Decision
Your teacher will do the soccer ball experiment. You will record the data in a
table like the one shown below.
Data Table. Mass Measurements
End Mass
Experiment
1
Pumping-up
Soccer ball
Experiment 2
Releasing Gas
from Plastic Bag
(after
pumping)
(after releasing)
___________ g
Start Mass
___________
g
(before
pumping)
(before releasing)
___________ g
___________
g
Change in Mass
= End Mass - Start Mass
___________
g
Class Average
Change in Mass
___________ g
___________ g
Uncertainty in Mass
__________ g
__________ g
Record the data in the Data Table on your record sheet.
If there is a
change, be sure to include a plus (+) sign for a mass increase or a minus (-)
sign for a decrease. Record the Uncertainty in Mass that you calculated in a
previous activity.
2. Did the mass of the soccer ball system increase, decrease, or stay the
same after your teacher put air into the soccer ball (taking into
account possible uncertainty)? Include your evidence.
3. Is the soccer ball a closed mass system when air is being pumped into
the ball? Write your reasoning.
Participate in a class discussion about your answers.
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Unit 4 Cycle 1
Experiment 2: Releasing Gas from a System (Chemistry in a Bag)
One day after school, a group of friends from a CIPS class were listening to a
story about an experiment called “chemistry in a bag.” The purpose of the
experiment was to determine if gases other than air had mass. Unlike the
soccer ball experiment, this experiment was one in which air or gas was an
output from the system.
In the experiment, the student put baking soda in one side of
a resealable plastic bag, and a small bottle of vinegar in the
other side. Then she carefully pushed as much gas as she
could out of the bag (without spilling the vinegar) and sealed
the bag.
When she tipped the liquid into the solid (without opening
the bag), the student observed bubbling. The bag inflated as
it filled with the gas from the bubbles.
After the bag inflated, the student measured its mass.
Then the gas was released from the bag, and the bag's mass
was measured again.
1. What do you think will happen to the mass of the plastic bag and its
contents after the gas is released? Why?
Participate in a class discussion of your predictions and reasons.
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Activity 5: A Massive Decision
You will do the “chemistry in a bag” experiment to test your idea. Your team
will need:
a resealable large plastic bag (two-gallon baggie)
a plastic cup or beaker
about 120 milliliters of baking soda
about 400 milliliters of vinegar
a mass balance
Follow standard safety rules
for using glassware. Clean up
any spills to prevent accidents.
Let’s Go!
STEP 1. Prepare your plastic bag with the baking soda in
one corner and the cup with vinegar in the other corner.
Push the air out of the bag and seal the bag. Make sure
the seal is tight!
STEP 2. Tip the vinegar onto the baking soda. You
may want to tip the bag back and forth to thoroughly
mix the vinegar and baking soda.
STEP 3. When there are no more bubbles, measure
the mass of the bag. Make sure the bag is completely
on the balance pan and does not touch anything else.
Record this Start Mass in the Data Table.
STEP 4. Open the bag. Release the gas, and then push
out the remaining air. Reseal the bag so that no air gets
back in.
STEP 5. Measure the mass of the bag again.
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Unit 4 Cycle 1
Record this End Mass in your data table.
STEP 6. Calculate the mass change (End Mass – Start Mass).
Record the mass change in your data table.
STEP 7. Post your team results in the Class Data Table.
When everyone has finished posting results, copy the class averages into
your Data Table.
Record the Uncertainty in Mass that you calculated in a previous activity in
the Data Table.
2. Did the mass of the plastic-bag system decrease or stay the same after
you let the gas leave the bag (taking into account possible measurement
uncertainty)? Include your evidence from the class data.
3. Is the bag with the baking soda and vinegar a closed mass system when
gas is released from the bag? Write your reasoning.
Participate in a class discussion about your answers.
Our Consensus Ideas
Think about the key question for this activity and discuss it with your team:
Do gases have mass?
1. Write your best answer on your record sheet. Include your reasoning.
Participate in the class discussion about your answers.
2. Record the class consensus idea(s) on your record sheet.
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