How do water striders walk on water?
Katrina Lustofin
(lustofin@uiuc.edu)
(ready to use)
ASK
Partner Projects
| GK-12 Teaching Fellowships |
Subject Areas
Grade Levels
Unit Keywords
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chemistry, insects, surface tension |
Rationale of the Unit
| To help students understand surface tension and hydrogen bonding between water molecules; can also help students understand ecological impacts of water pollution |
Background and Resources
What I am discovering
See attached word file for the experiment.
We used different types of detergents (dish soap, shampoo, laundry detergent, etc), salt, starch and sugar as our chemicals. Other liquids used in addition to water were methanol and lamp oil.
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Dialogues, Discussions, and Presentations
After doing the experiment, we had the students discuss their results. Addition of soap decreased surface tension and made the arthropods sink. Addition of starch or salt only slightly decreased surface tension. Using lamp oil did not seem to change surface tension as measured, but the insects would not sit on the surface of the lamp oil. Susan used this as a jumping off point to discuss bonds between molecules, particulary hydrogen bonding, in a later class.
We then told the students that water striders are sometimes used as indicators of water pollution and asked them to tell us why that might be. Students were good at making the connection between the toy not sitting on the surface of the water and water striders not being able to walk on water. We discussed the need for aquatic insects to breath and how oil slicks especially might interfere with this.
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Assessment, Related Questions, and Story of the Unit
| The experiment went quite well. I think it was effective at peeking the students interest. The lamp oil did not behave quite as expected (relative surface tension measured was high but the arthropod toy would not sit on the surface) - something to investigate further. Students who had done previous reports on soap had a better grasp of the chemistry behind the experiment. |
Uploaded Files:
ChemicalBondingLab.doc
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