Catherine Barry
February 9, 2011
The Great Soda Density Experiment
This discrepant event is intended for Grade 8 in the Science Fluids Unit: Floating
& Sinking – Density.
Science Concept: The Great Soda Density Experiment is a discrepant event
which links with the concept of fluids, density and buoyancy. This activity can be
used to reinforce the curriculum outcome 307-8: describe the relationship
between the mass, volume, and density of solids, liquids, and gases using the
particle model of matter
Target Misconceptions: Students will likely assume that all of the cans of pop will
either float or sink.
Materials:
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Transparent plastic container
1 can Coca Cola
1 can Diet Coke
1 can Pepsi
1 can Diet Pepsi
Pre-assessment:
Ask students to list in their notebooks “Coca Cola”, “Diet Coke”, “Pepsi” and “Diet
Pepsi” and beside each pop can type, write “”float” or “sink” depending on what
they think will happen to each can. Ask students to label this table their
“Hypothesis”.
Prompts:
Tell students that each can is made of the same material and have the same
volume and are filled with the same amount of pop.
Before proceeding with the event, you may wish to ask some of these questions:
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Do you think the pop cans will float or sink?
Why?
After the event has taken place, you may wish to ask some of these questions:
 What are the similarities between the cans that floated?
 If they are all the same volume, why didn’t they all sink/float?
 What are the differences between the cans that sank and the cans the
floated?
 What is it that determines whether or not something sinks or floats?
 Why is the density different in Diet and Regular pops?
 Which is denser?
 If we shrunk the can of regular pop to only half of its volume, would it float
or sink?
Explain that density is a characteristic property of a substance. Example: Water
has the same density, no matter what its volume. Same goes for wax, vegetable
oil, clay, iron, etc.
Procedure:
1. Fill up the plastic container until it is about three quarters full, with room
temperature water.
2. Place each pop can into the water and hold them upright at the bottom of
the container for a few moments before releasing them.
Expected Results: The can of Regular Coca Cola (and any other regular pop)
should sink and the diet Coke (and any other diet pop) should float.
Explanation:
This discrepant event demonstrates that the density of pop cans with the same
volume can differ. The density of a fluid is determined by not only the volume of
the fluid, but the mass of the fluid as well. In this case, the ingredients of Coca
Cola and Diet Coke (as well as, Pepsi and Diet Pepsi) differ. Coca Cola contains
sugar, whereas aspartame is used as the primary sweetener in Diet soda pop
beverages. There is about 30-40 grams of sugar dissolved in one can of pop
(about 9 table spoons). Only 4 table spoons of aspartame are used in each can
of diet Coke. Therefore, Diet Coke has a smaller mass then regular Coke.
Teaching suggestion:
If students get caught up on the “weight” of an object determining whether it
floats or not, drop a penny into the water. The penny weighs less than the Diet
Coke can, however it sinks to the bottom of the container because the penny is
more dense than the Diet Coke can.
Extension:
a) Show the class what 9 table spoons of sugar looks like by placing this amount
of sugar in a ziplock baggy. Do the same for 4 table spoons of aspartame.
b) You may also choose to discuss the ways that one could get the can filled with
regular pop to float without opening the can. One suggestion might be to shake
the can, which would cause some gas to come out of the solution, however
because the can cannot expand, (its volume is not increased) and the amount of
pop remains the same (mass is not decreased), the density cannot change.
Therefore, the pop can will still sink. You may choose to “prove” this to students
by shaking the can and placing it back in the water. Another suggestion may be
to attach something to the outside of the can in order to increase its volume, but
not increase its weight significantly.
c) Challenge students to make a small object, which ordinarily sinks, float.
Provide them with small objects (plastic figures, marbles, or keys that sink), as
well as materials that float (cork, zip-closing plastic bags, Styrofoam). Give
students time to assemble their objects and test them in a container of water.
Tell students that life jackets work in a similar way. Ask students why a life jacket
helps a person to float. Explain that a person wearing a life jacket floats because
of the combination of the body and the life jacket is less dense than water.
Have students explain how they made their objects float. Ask students what all of
these floating objects have in common. Students should realize that mass is
increased slightly, while volume is increased much more. When the density of
this larger combined object is less than the density of water, it floats.
Real-Life Example:
Ask students to imagine that the class is going on a canoe trip and that we are
packing our cooler full of food, water and pop. Ask students “what kind of pop
would we want to pack for our lovely canoe trip?”.
Sources:
http://www.inquiryinaction.org/classroomactivities/activity.php?id=42#test_buoya
nt
Diagnosing and Dealing with Student Misconceptions: Floating and Sinking
by Yue Yin, Miki K. Tomita, and Richard J. Shavelson, Science Scope, April
2008, p. 34-39