Macroscopic Observations Clear Cold Solid It melted as we watched No smell http://www.worldofmolecules.com/interactive_molecules/ice.htm Micromodels Click on the link to go to an interactive ice molecule. Right below on the same linked page there is also an interactive liquid water molecule. The red balls are oxygen(O) and the white ones are hydrogen(H). Water/ice has polar covalent bonds. Each water molecule is connected to another one through Hydrogen bonds. Notice that the ice molecules are spaced out further than the water. That is why ice is less dense and floats in water. These molecules were created with the Jmol App and are a part of the “World of Molecules” website which can be found with this link.
Macroscopic Observations Static electricity pulled the water toward itself The balloon had to be pretty close before it attracted the water http://www.csiro.au/helix/sciencemail/activities/images/Wat erBendMolecules.gif Micromodels Click on the link below to go to a picture that shows why the balloon pulled the water toward itself. You will see a negatively charged balloon(when you rubbed the balloon on your hair you gave the balloon electrons or static electricity. This attracts the positive ends of the water molecules and makes them align. The positive parts of the water molecules are hydrogen and the negative is oxygen. This is a good example of intermolecular forces. One thing it doesn’t show is that before the water molecules get close to the balloon they aren’t aligned. This model is part of the “Science by Email” website
Macroscopic Observations Static electricity pulled ethanol toward itself Had a slightly stronger reaction than water Smelled like gas Micromodels This is a model of static electricity attracting ethanol. The balloon shown is negatively charged after being rubbed on someone’s hair. The nonpolar ethanol has a positve end so it is attracted to its opposite. This makes the molecules align with the balloon and change the water current. The red is oxygen, the greens are carbon, and the others are hydrogen for the ethanol. The ethanol molecules are from “The Interactive Library” at Edinformatics.com and the balloon is from the “Science by Email” website.
Macroscopic Observations No reaction Splashes on the counter evaporated quickly Micromodels This model shows that hexane does not react to the negatively charged balloon. Hexane is nonpolar so it doesn’t have opposite ends(positive and negative). This means that nothing will be attracted to the balloons electrons and so the hexane won’t align with them. Since nothing attracts, the flow of hexane doesn’t change. The hexane molecules were created by Ben Millis and were found on “Wikimedia Commons.” The balloon was found on “Science by Email.”
What is being aligned? Why doesn’t some water/ethanol get pushed away from the balloon even though there is also a negative side to the molecule?
Macroscopic Observations Evaporated pretty quickly on glass Evaporated slowly on plastic 2 drops for the microspatula Easy to pull glass apart Easy to pull plastic apart Plastic Glass Micromodels Ethyl alcohol evaporates a little slower than acetone but faster than water. Ethyl alcohol can cohere and adhere much better than acetone but not as well as water. Hydrogen bonds form between hydrogen and oxygen on the glass so that adheres. Ethyl alcohol has oxygen in it so that makes it able to cohere but because of its structure it doesn’t have as strong of a cohesion as water. Since it doesn’t hold itself together as well it separates and then evaporates. The black lines are bonds and the red is oxygen.
Macroscopic Observations Didn’t evaporate while we watched 2mm height on glass 10mm width on glass 2.5mm height on plastic 5mm width on plastic 3 drops for microspatula Easy to pull apart on plastic Kind of hard to pull apart glass PlasticGlass Micromodels These models show why water didn’t evaporate as fast as the other two did. The green lines within the water droplet are hydrogen bonds that hold water molecules together. That is called cohesion. Water also forms a bond with the plastic which is called adhesion. The hydrogen in the water forms a hydrogen bond with the oxygen in the glass. Since everything is bonded together it takes a lot longer to break them apart and for the water to evaporate. The black lines are also hydrogen bonds. The red on the glass is oxygen. Glass Plastic
Macroscopic Observations o Evaporated the quickest of the three o Evaporated a little quicker on plastic than on glass o 2 drops for the microspatula o Hard to pull glass apart o Easy to pull plastic apart PlasticGlass Micromodels Acetone evaporates quickly because it can’t cohere. It can adhere to other things with hydrogen bonds but since it doesn’t bond with itself it can’t hold itself together and avoid evaporation. The hydrogen in acetone can form a hydrogen bond with the oxygen in glass but there is nothing for it to bond with in plastic. This makes it evaporate faster on plastic. The black lines are hydrogen bonds between the white hydrogen and the red oxygen. The green is carbon and the red in acetone is oxygen. Plastic
Why does acetone evaporate so quickly? Why can’t acetone cohere? Why did the alcohol evaporate almost as quickly as the acetone if it bonds a lot better?
Macroscopic Observations Bubbles came mainly from the penny Penny shook a lot It created a nucleation site Bubbles were larger than before Micromodels This is a model of what happened when we dropped the penny into the boiling water. It created a nucleation site in the beaker which allowed many bubbles to form on the penny. A nucleation site is just an area with many holes or rough spots that bubbles can form in. Since there are so many rough spots on a penny there were a lot of bubbles forming there. Red/purple=oxygen white=hydrogen
Why do some bubbles go straight up and others zigzag? Why did some bubbles get stuck at the surface for awhile and others went through quickly? Why did some bubbles form on the side instead of the bottom later on?