cohesion, surface tension, and adhesion
TRANSCRIPT
![Page 1: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/1.jpg)
Cohesion, Surface Tension, and Adhesion
![Page 2: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/2.jpg)
Content Objectives
• SWBAT describe how hydrogen bonding allows water molecules to maintain strong cohesion, adhesion, and surface tension.
![Page 3: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/3.jpg)
Van der Waals Forces
• The sum of all attractive forces between molecules.
![Page 4: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/4.jpg)
Hydrogen Bonding
• Attraction between hydrogen atoms who are bonded to strongly electronegative atoms like O, F, or Cl and another polar molecule.
• Water is attracted to itself due to hydrogen bonding between H---O
![Page 5: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/5.jpg)
Surface Tension
• Refers to how strong molecules hold onto each other against gravity or other forces.
• Water has strong surface tension that allows it to form almost completely spherical droplets.
![Page 6: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/6.jpg)
Surface Tension
![Page 7: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/7.jpg)
Water Striders Take Advantage of Surface Tension
![Page 8: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/8.jpg)
Why Do Ice Cubes Float?• Hydrogen bonding keeps the water molecules well
spaced as they form their crystalline structure.
• Thus, the density of the solid is actually less than the liquid. This is rare among compounds.
![Page 9: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/9.jpg)
Hydrogen Bonding of DNA and Proteins• Hydrogen bonding is what keeps a DNA
molecule in its double helix.
• It is also what allows proteins to bend into the critical shapes.
• If you heat a protein, it will break the hydrogen bonds and it will fall apart.
• If that happens you die…
![Page 10: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/10.jpg)
Cohesion• Attraction between like molecules
• Mercury is more attracted to itself than the glass, so it does not “wet” it.
• Mercury will roll over surfaces without attaching to them.
![Page 11: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/11.jpg)
Adhesion
• Attraction between dissimilar molecules
• Water has a tendency to stick to many other substances, like these spider webs or pine needles.
![Page 12: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/12.jpg)
Adhesion
• These attractions can be due hydrogen bonding, polar attraction, or other dipole-dipole interactions.
• Geckos use adhesion to climb upside down and on almost any surface.
![Page 13: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/13.jpg)
Meniscus
• Water is attracted to glass and has a tendency to climb up its surface due to adhesion.
• Glass is polar, because it is primarily SiO2
![Page 14: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/14.jpg)
Wetting Vs. Non-wetting
• Gallium does not have much cohesion. It is much more attracted to other surfaces than itself.
• Here it has wet the surface of the glass and it is hard to get off again.
![Page 15: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/15.jpg)
Wetting vs. Non-wetting
• A is a liquid with little adhesion to the surface (thus non-wetting)
• B is a liquid with moderate adhesion
• C is a liquid with significant adhesion and thus is wetting the surface.
![Page 16: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/16.jpg)
Capillary Action• Is the ability of a liquid to climb against gravity
on the surface of something else.
• The higher the level of adhesion between the two and cohesion within the liquid, the more rapidly this can occur.
![Page 17: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/17.jpg)
Capillary Action of Water in Concrete
![Page 18: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/18.jpg)
Capillaries
• Capillaries are tiny blood vessels that deliver blood to individual cells.
• At their tiny size, the pressure of the heart is not enough to force the blood through them.
• The blood moves through the blood vessels through capillary action.
![Page 19: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/19.jpg)
Using Surface Tension to Walk on Water
• Aquatic insects have surface hairs that do not allow water to wet it. Then, they use the surface tension of water to crawl across it.
![Page 20: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/20.jpg)
Definitions• Cohesion allows the water droplets to stay together.
• Surface Tension makes them bead up.
• Adhesion keeps them attached to the leaves instead of running off.
![Page 21: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/21.jpg)
What to Do?
• What do you do if you get butter or vegetable oil on your hands?
![Page 22: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/22.jpg)
Soap
• Water won’t get grease off your hands, so you use soap.
![Page 23: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/23.jpg)
What IS soap anyways?
• Lard (animal fat)
• Vegetable oil
• Caustic NaOH or KOH pellets or lye water
![Page 24: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/24.jpg)
Soap• How does soap do it?
• Soap molecules contains a polar head and a non-polar tail.
• The oils dissolve into the non-polar tail and then the polar head is attracted to and pulled away by the running water.
![Page 25: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/25.jpg)
What About Tough Grease?• Soap often is not strong enough to get off motor
or bike grease
• Use vegetable oil first!
• Non-polar grease will dissolve into the oil.
• Then, soap will remove the vegetable oil.
![Page 26: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/26.jpg)
Surfactant• A substance that disrupts and lowers the surface
tension of a liquid.
• Detergents contain a polar and non-polar end. When added to water, they attach to water, but do not allow waters to attach to each other, thus lowering the surface tension.
![Page 27: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/27.jpg)
How Bubbles Form
• Bubbles form when surfactants surround water molecules.
![Page 28: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/28.jpg)
![Page 29: Cohesion, Surface Tension, and Adhesion](https://reader030.vdocuments.net/reader030/viewer/2022012617/619f3d84d27aaa1f6a138768/html5/thumbnails/29.jpg)
Content Objectives
• SWBAT describe how hydrogen bonding allows water molecules to maintain strong cohesion, adhesion, and surface tension.