Lab 13

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Date
Lab 13 Water on a Penny
Purpose
To see how soap affects hydrogen bonding in water.
Question How will adding soap to a water
solution effect how many drops will fit on top of
a penny?
Hypothesis _____________________________________
____
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Chemical Background
Water molecules are cohesive (they stick to each
other) because of the hydrogen bonds formed
between them.
3
Water molecules at the surface are pulled from
both sides and experience surface tension.
4
The paper clip is floating because of surface
tension. The water molecules are like a stretched
sheet
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Experiment 1. Using dropper, consistently drop
water onto the penny. Count the drops and record
data.
Tap water or soapy water
Tap Water Soapy Water
Trial Number of drops placed on penny before breaking surface tension of water Number of drops placed on penny before breaking surface tension of water
1
2
3
4
Average
Class Average
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Group Tap Average Soap Average
1
2
3
4
5
6
7
8
9
10
11
12
13

Class Average
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Properly Graph your individual data (averages)
along with the class average data on the same
graph...in color! Remember to include all things
needed on a graph!!
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Conclusion Remember the 3 parts!!
Questions

1. What is the independent (manipulated) variable of
   this experiment?
2. What is the dependent (responding) variable of
   this experiment?
3. What are some of the controlled variables for
   this experiment?
4. If some groups did their trials heads-up and
   others did their trials tails-up, should the
   data be combined for a class average.
5. Why should the average be a whole number?
6. How could you design this experiment to account
   for the fact that a person gets better at
   dropping?
7. Do you think that knowing ahead of time that
   soapy water decreases the surface tension of
   water could bias your results?