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What's
the Matter with
My Jell-O?
Background
Information
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Summary:
Students work in teams of four as they conduct four controlled Jell-O experiments
over a two-day period. Styrofoam, sugar, salt, and room temperature treatments
are compared to control Jell-O to investigate the effect of these treatments on
the phase change of Jell-O from liquid to solid (freezing point). The Take It
Further section explores the environmental pros and cons of using salt (one of
the Jell-O treatments) to improve roadway safety. The Family
Page extends this learning to the community by providing families with challenges
to explore at home.
Related Topic(s):
matter (states, properties), atoms, mixtures (colloids, solutions), environmental
effects of salting roadways, variables (control vs. treatment), qualitative
vs. quantitative analysis, freezing point, melting point, physical change
Ohio Academic Standards Alignment: Click here to view content standards alignment to Science for Ohio by grade level.
Classroom Time Required:
135-150 minutes as follows:
- Day 1: 90 FULL
minutes
- Day 2: 45 minutes for
final observations and PutItAllTogether
Note: If you are not self-contained, make arrangements ahead of time
for a block schedule for Day 1.
Background Information:
- Matter and Phase
Change. There are four states of matter: solid, liquid, gas, and
plasma. The term phase change refers to the changing of some
form of matter (in this case Jell-O) from one state to another. Jell-O
phase changes from liquid to solid. Boiling water, on the other hand,
phase changes from liquid to gas.
- Freezing point. Freezing
point is the temperature at which a liquid becomes a solid. "Freezing
point" implies the need for heat energy to be removed in order to cause a
phase change. The freezing point of water is 32 degrees Fahrenheit.
The freezing point of Jell-O is approximately 85 degrees Fahrenheit.
The freezing point of some metals may be 1000 degrees Fahrenheit or more!
- Melting point.
Melting point is the temperature at which a solid becomes a liquid.
"Melting point" implies the need for heat energy to be added in order to cause
a phase change. Melting point temperatures are often similar to freezing
point temperatures for the same matter.
- When Jell-O cools,
is it a physical change or a chemical change? The cooling of Jell-O is
a physical change because the Jell-O has changed form through cooling rather
than a chemical reaction. When heated, the Jell-O becomes liquid again. On
the other hand, a chemical change such as the burning of wood involves a chemical
reaction (the release of energy and carbon) which makes it difficult to return
the matter left after burning into wood again.
- Variables: Control
vs. Treatment. In any experiment, the control sample is the one
that you don't mess with. The treatment sample is the one that you do
mess with. By having a control sample, you have a basis to evaluate
the effect of the treatment sample (in this case salt, sugar, Styrofoam cup
insulation, or room temperature).
- Qualitative Analysis.
Qualitative analysis, or non-numerical observations, will be conducted using
a straw before, during, and after phase change of the control Jell-O.
Students can come up with their own tests or the following tests can be used.
Regardless of the test, emphasize comparing the control and treatment Jell-O
results.
- Density Test: Stick
the straw down through the center of the Jell-O and let go. Low density:
the straw falls over. High density: the straw stays upright.
- Pressure Test: Drop
the straw from approximately 5 cm above the Jell-O. Does the straw enter
the Jell-O quickly, slowly, or not at all?
- Slurp Test: Slurp
the Jell-O up the straw. Does it slurp like a solid or a liquid?
- Salt. Salt lowers
the freezing point of most liquids. Roadways are salted in the winter
for this reason. Snow which normally phase changes to liquid at 32 degrees
Fahrenheit can be kept from freezing down to 15 degrees or lower when mixed
with salt. Although this makes our roads safer in the winter, it also
contributes to pollution of watersheds, including ground water, creeks, rivers,
and ponds, which is harmful to wildlife. See Related Resources
for more information.
- Expected Results.
Expect the control Jell-O to phase change after an hour or so. Expect
the sugar treatment to phase change, but be slightly less solid than the control
after an hour or so. Expect the room temperature treatment to phase
change in two to three hours. Expect the Styrofoam treatment to phase
change completely, but take longer than the control. Expect the salt
treatment to remain liquid.
- Cautions. Discuss
with your students the safe use of hot water during the experiment.