Lab Report
Title:____
Question:
What is the effect of different amounts of soap on the surface tension of water? (identify m.v. & r.v.)
Background Information:
Properties of water: https://www.youtube.com/watch?v=0eNSnj4ZfZ8
One of the properties of water is surface tension, or cohesion. This refers to the ability of water molecules
to stick to one another. This is also the reason that “water striders” can walk on the top of the water without falling
through.
Soap is a surfactant, which is a “chemical agent that is capable of reducing the surface tension of the liquid
in which it is dissolved”.
Hypothesis:
If ______
then _____
because _____
Materials:
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


400-mL plain water in a 600 mL
beaker
15-mL AJAX orange dish soap
(2) 100-mL beakers
one penny (use only one side)
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
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stir stick
two pipettes
paper towels
Procedure:
1.
Pour 15-mL dish soap into 100-mL beaker at supply station. Gather remaining materials and take to lab
station.
2. Place penny onto a paper towel on a vertical, solid surface.
3. Fill empty 100-mL beaker with 30-mL water.
4. Fill the second pipette with plain water from the small beaker, hold pipette vertically and drop liquid in the
pipette slowly onto the penny while counting the number of drops. Continue dropping water until water
flows off of penny. Record____________________. Repeat trial 3 more times and record
______________________ for each trial. Compute average drops per trial and record average onto data
chart.
5. Rinse and empty beaker and pipette used for dropping liquid onto penny.
6. Refill 100-mL beaker with 30-mL water. Add 3 drops of soap using “soap” pipette”. Stir soap solution
gently.
7. Repeat steps 4-5 for soapy water.
8. Refill 100-mL beaker with 30-mL water. Add 9 drops of soap using “soap” pipette”. Stir soap solution
gently.
9. Repeat steps 4-5for soapy water.
10. Refill 100-mL beaker with 30-mL water. Add 18 drops of soap using “soap” pipette”. Stir soap solution
gently.
11. Repeat steps 4-5 for soapy water.
12. Clean up excess water with paper towels, then clean and return everything to its proper place.
Data:
(title)
Manipulated Variable vs. Responding Variable
Manipulated Variable
(units)
Responding Variable
(units)
Trial 1 Trial 2 Trial 3 Trial 4
Average
Lowest condition
Condition 2
Condition 3
Highest condition
Analysis:
Create a hand-drawn line graph following the data table in your lab report. It should have a title,
the trials (of dropping liquids—manipulated variable) along the bottom and the number of drops
(responding variable) up the right side. The different CONDITIONS should be represented by
different lines (of different colors). Provide a “key” or “legend” that shows what condition each
trial represents.
Conclusion:
0 Write a conclusion for this experiment.
In your conclusion, be sure to:
 Answer the experimental question.
 Include supporting data from the Soap vs Surface Tension Data table.
(low AND high data averages)
 Explain how these data support your conclusion.
 Provide a scientific explanation for the trend in the data.
Question: What is the effect of different amounts of added soap on
the surface tension of water?
Conclusion: (use FIVE bullet points)