Earlier this week, our class did three experiments to test the properties of water. Some of the properties of water displayed in these experiments were cohesion, adhesion, and surface tension. Adhesion is when water sticks to another substance. Cohesion is when water sticks to water, and it goes along with surface tension, which is defined as the “tendency of water molecules to attract one another”. Surface tension and cohesion are what cause the “skin” like covering that makes it possible for water to build the dome shape that it has when you pour a glass of water a little bit above the rim. In all three of these properties water tends to be “sticky”. It either sticks to itself or to another substance. This quality of water is present in all of these experiments.
In the first experiment that we did, we were testing how many drops of water we could place on a penny before it would spill over. We also tested how many drops of alcohol could be placed on the penny. I hypothesized that the penny would hold more drops of water than it would alcohol. So I began by testing the water on the penny. I took a pipette and filled it with the water, then slowly began to drop the water on the penny, one drop at a time. I was able to get fifty drops of water on the penny before it spilled off. Next, I filled the pipette with alcohol and began placing the drops on the penny. This time, I was only able to place thirty drops on the penny before it spilled over. My hypothesis was correct, the penny held more drops of water than of alcohol. The reason that the penny could hold more water is because of waters properties of cohesion and surface tension. The hydrogen bonds in water make the molecules stick together, so all of the drops of water began sticking to each other. The alcohol doesn’t have the same hydrogen bonds, so it doesn’t build up like the water does. The water began to form a large dome shape due to surface tension. I could continue to place drops of water on the penny because it would just keep sticking together and building the dome until it spilled over the raised edge of the penny. The properties of cohesion and surface tension have importance to living organisms. For example, trees are able to get water from the roots all the way up to the leaves because of these properties. Trees have tons of tiny tubules that run from the roots to the top. The water sticks to the sides of these tubes because of cohesion and as more water comes into the roots, the water creeps up the tubes all the way to the leaves. So in conclusion, my results proved my hypothesis to be correct, and through this experiment, I learned about how surface tension works.
In the second experiment, we tested the behavior of a drop of water on a piece of wax paper. We were trying to see what would happen to the water when we tried to cut it in half with a toothpick. I hypothesized that when I tried to cut water in half, it would separate the drop and make two separate drops. So I then began the experiment by gathering the needed tools which were a piece of wax paper, a pipette, a toothpick, and water. Using the pipette, I placed a drop of water on the sheet of wax paper. The water formed a circular dome, almost the shape of a sphere, but it was flattened on the bottom and top. Then, using the toothpick I tried to slice the drop in half, but it wouldn’t cut. Instead, the drop either moved around the toothpick, or drag along with the pick. This experiment also displayed the property of cohesion. The water sticks to itself on the wax paper instead of spreading out. If I were to place this drop of water on a piece of notebook paper instead of the wax paper, it would make a complete difference. The wax on the wax paper is what helps the water drop hold its shape because the wax is a hydrophobic surface. If the water was on notebook paper, the drop would just absorb into the paper instead of sitting on top of it. The results of this experiment were not what I hypothesized because the toothpick did not separate the drop, but it drug the drop across the paper.
In the third experiment, we were testing ways to get water from one beaker to travel down a sting and end up in another beaker. I hypothesized that we could just start pouring the water onto the string and that it would just begin to go down it into the other beaker. So I tried to do this with a string about a foot and a half long. I quickly found out that this was not going to work. The water did not travel down the string what-so-ever. I had to think of ways that I could get the water to actually stick to the string so it would travel on it. I got the idea to wet the string before pouring the water on it. This helped tremendously. The water was actually making it to the other beaker. So I decided to try it with a longer string. The same procedure worked on a string approximately four feet long, and on another about six feet long. I tried the experiment on a string about ten feet long, but couldn’t get it to work. So the longest string that I could get the water to travel down was about six feet in length. This experiment was an example of the adhesion property of water, and could also be an example of cohesion. Adhesion is what makes the water stick to another substance. Because the string was wet, it was helping the water stick to the string. When the string was not wet, the water didn’t stick at all. So both of these properties contributed to the experiment by helping the water stick to itself and another substance.
cecelyfranz 
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