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6th Grade
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We are going to explore:
 Examination of changes in
surface tension of a liquid
between water and water with
soap added
 The effects of soap on the
surface tension of water
 How soap affects the cohesion
of water molecules and the
number of drops of water that
can fit on a penny
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Brainstorm…
 What do I know about water
molecules and soap?
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Title
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Laboratory Report:
_Drops on a Penny_
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Research the following terms:
 Surface Tension
 Cohesion
 Surface Tension: the force that causes the
molecules on the surface of a liquid to be pushed
together and form a layer
 Cohesion: molecular attraction by which the
particles of a body are united throughout the
mass

Problem:
 Does adding soap to a penny
reduce the surface tension of
the water being added?
OR
 How does adding soap to a
penny affect how many drops
can fit on it?

Hypothesis
Example
 If soap is added to a penny,
then more drops of water
will fit on the penny.

Experiment Materials:
 Part A: Penny, paper towel, eye dropper, 100%
water solution
 Part B: Penny, paper towel, eye dropper, 75%
water & 25% soap solution
 Part C: Penny, paper towel, eye dropper, 50%
water & 50% soap solution


Manipulated (Independent) Variable: the
soap (what is added by you, the scientist!)
Responding (Dependent) Variable: number
of drops of water that are able to be added
(the quantitative observations collected in
the data table)
 * not included on Laboratory Report: Control
 Control: adding water to the penny without soap

Safety Rules:
 Always wear safety goggles when experimenting with

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chemicals (soap).
Never taste chemicals (or other substances) used for a lab
experiment.
Keep lids on all containers when not in use.
Clean up spills immediately.
If any substance gets into your eyes or in a cut on your
skin, notify your teacher and follow his/her directions.
Wash your hands before and after an experiment.
Clean up your lab area and materials after an experiment
and return materials to their proper location.

Experiment Procedure
1. Rinse penny in tap water and dry completely
2. Place the penny on paper towel
3. Get solution (1, 2 or 3) and eye dropper
4. Use eye dropper to place drops of water on the
penny (1 at a time) until water runs over edge
5. Record the number of drops for that trial in the
table & calculate mean after 5 trials

Data:

Results: Bar Graph of the Average of the three liquids:

*Example has 2 Bars, yours will have 3 bars, for the
3 solutions!*

Conclusion:
Example
 My hypothesis was unsupported. Soap decreased
the number of drops of water that could be
added. In Part A, the mean number of drops that
could be added to the penny were….