Name: ____KEY______Date: ______Per: ______
Introduction to Science: LAB ACTIVITY
Surface Tension of Water
Surface tension refers to water’s ability to “stick to itself”. Surface tension can be measured and observed by dropping water onto a penny. The more drops that fit onto the penny means a greater surface tension, the fewer drops means a lower surface tension.
Purpose: To design and test a hypothesis.
Problem: How does soap affect the surface tension of water?
Materials:
-One penny
-Beaker with plain water
-Beaker with soapy water
-2 droppers
-paper towels
Initial practice trial: Use the plain water dropper to see how many drops of water you can fit on the penny. Make sure that the dropper does not come in contact with the water on the penny. Record the number of drops below.
Initial trial number of drops ______
Before beginning lab, develop a hypothesis that answers the problem statement above. Remember to form you hypothesis using an “if, then” statement. Record your hypothesis below.
These are examples of how your hypothesis might look:
“If we add soap to water, then the surface tension will______.”
‘If we add soap to water, then the number of drops will ______.”
“If we add soap to water then the stickiness of the water will ______.”
Procedure:
Test your hypothesis by comparing the number of drops of plain water that can fit onto a penny to the number of drops of soapy water that can fit onto a penny. Complete five trials for each. Try to hold the dropper in the same way each time. Record your data in the table below.
SAMPLE DATA
Number of Drops of Plain Water and Soapy Water on a PennyTrial 1 / Trial 2 / Trial 3 / Trial 4 / Trial 5 / Average
Plain Water / 27 / 24 / 31 / 25 / 26 / 26.6
Soapy Water / 14 / 17 / 13 / 13 / 16 / 14.6
Examining your Hypothesis – Read your hypothesis written in Part A, Number 3. Consider your hypothesis and the results of the experiment to answer the questions below.
Identify the parts of the above experiemnt:
Control Group: Plain Water Experimental Group: Water with Soap
Independent Variable: Amount of Soap Dependent Variable: Number of Drops
Constants: Penny, Side of Penny, How the drops were dropped, number of trials
Analysis:
- Based on the analysis of your data, explain how adding soap to water affects the surface tension of water.
The data shows that as soap is added to water, the number of drops the penny is able to hold decreases. A lower number of drops means the surface tension of the water decreased.
2. Does your data appear to support your original hypothesis? Depends on hypothesis
Explain why/ why not. The data supports that adding soap lowers the surface tension of water. The data would not support that adding soap would increase the surface tension.
Conclusion:
- Based on your data, would you accept or reject your hypothesis? Depends on hypothesis
Explain how your data supports/ does not support your hypothesis.
If the data supported your hypothesis, then you would accept it.
If the data does not support you hypothesis, then you would reject it.
- Suggest a reason why it was best to complete many trialsand calculate the average rather than completing only one trial when drawing conclusions about your hypothesis.
If you only do one trial your results would be affected if it was not correctly done. If you complete many trials and only one was not correctly done, the results would still be meaningful. The more data you collect the more valid your results will be.
- In any experiment, why is it important to test only one variable at a time?
If you test more than one variable, then you may not know for sure which variable caused the change to occur. By only having one variable, you can link the independent variable directly to the dependent variable.