(no subject)
Pre Questions:
1.) Surface tension is the explanation of cohesive forces on the surface of water, where the hydrogen bonds pull the water molecules together, causing them to pool into droplets of water on flat surfaces, form raindrops, or hang over the edge of a flat surface without spilling, etc.
2.) Heating water can lower its surface tension. This lowers the surface tension because it causes some of the hydrogen bonds to break, therefore lowering the level of cohesion among water molecules, and taking away some of their previous surface tension.
3.) Water striders can walk on water because of surface tension. The forces of the water molecules clinging together cause it to become like one body, with a small force repelling other weak forces away (such as the light gravitational pull on a water strider). I also read that most species of water striders have greasy feet. This would certainly enable them to walk across the water, since oily substances are hydrophobic, and would have a force that naturally repels water away, and vice versa.
4.) Cohesion is the attraction of two like molecules to each other (in this situation, the attraction of water molecules to other water molecules).
5.) A surfactant is a chemical or substance that lowers the surface tension of water. The surfactant (detergent for example) is composed of one part non-polar tail that is hydrophobic --- water-fearing. Because detergent molecules tend to collect at the surface of the water they are mixed with, their non-polar tails stick out of the water because, naturally, they are water fearing. This disrupts the hydrogen bonds at the surface, reducing the surface tension dramatically. (C: Conceptual Physical Science, 1999 p. 443)
Post Questions:
1.) The container with the least surface tension was container D, with the hot H20 and the detergent. This is because the heightened temperature of the water broke some of the hydrogen bonds, causing a decrease in cohesion among the water molecules. The detergent also decreased the surface tension because it disrupted the hydrogen bonds since it is hydrophobic, and the hot water speeded up the mixing in of the detergent.
2.) The container with the greatest surface tension seemed to be container A, with the cold, plain water. Although our results do not directly show this, container one seemed to hold the steadiest, most cohesive water, not only because of its dome-like shape, but also because when we picked it up to dump it into the sink, it spilled less than the others did.
3.) Heat disrupts the hydrogen bonds and breaks them, so there isn’t as much cohesion as there is in a sample of water at a cooler temperature. This is because the hydrogen bonds are more easily maintained in that situation, and therefore there is greater surface tension.
4.) Detergents contain hydrophobic hydrocarbon tails, and a hydrophilic “head” group. This means it is a “surfactant.” When detergent reacts with water, it disrupts the hydrogen bonds, thereby reducing the surface tension of the water.
5.) A dome was able to form on the top of the water containers because the water was piled above the brim of the cup, however the water stuck to itself, and kept from spilling. The hydrogen bonds and the cohesion kept all molecules of water sticking together, and so a dome shape was formed because it was the most favorable shape possible, assuming that the water molecules were all to stay entirely bonded to each other.
Conclusion:
The purpose of this experiment was to see surface tension in action. It provided a visual guide to aid in our understanding of how surface tension works exactly in the real world, and not just in concepts in text books. By completing the experiment, we also learned the conditions under which surface tension is higher or lower.
Our results were significant because they actively portrayed which circumstances support surface tension, and which do not. When we compared cup A, plain cold water, with cup B, water and detergent, cup A seemed to be much stiller, and did not spill, even after 100 paper clips. Although during our experiment cup B did not spill either, it was impossible to move without slopping the soapy water all over the lap table. The same was true for cup C, of hot water; it did not spill after 100 paper clips, but when we so much as touched the rim of the glass, a drop of water ran down the side. It seemed, however, that the detergent cold water spilled more readily than the plain hot water. With cup D, however, the combination of the hot water and the detergent seemed to be what made the water go over the top and spill out with only 91 paper clips.
There were, however, some very prominent sources of error. For one thing, the cups were definitely not filled to an equal height. They looked close, but it is impossible that they were all filled to the exact same caliber. Another source of error was the amount of detergent mixed with the water; because it was difficult to make clear droplets come from the bottle, we tried to just squirt an equal amount into the two cups that required detergent, but this, too, was hard to be perfectly accurate on. Both of these things could have disrupted our data, and lead us toward the wrong conclusion. However, after completing the experiment fairly successfully once, we were able to testify that we think the surface tension is greatest in cooler, purer water, in which there is much opportunity for hydrogen bonding, in contrast to the warm, and/or soapy water. The higher the accommodations for hydrogen bonding cohesion with water molecules, the stronger the surface tension.
1.) Surface tension is the explanation of cohesive forces on the surface of water, where the hydrogen bonds pull the water molecules together, causing them to pool into droplets of water on flat surfaces, form raindrops, or hang over the edge of a flat surface without spilling, etc.
2.) Heating water can lower its surface tension. This lowers the surface tension because it causes some of the hydrogen bonds to break, therefore lowering the level of cohesion among water molecules, and taking away some of their previous surface tension.
3.) Water striders can walk on water because of surface tension. The forces of the water molecules clinging together cause it to become like one body, with a small force repelling other weak forces away (such as the light gravitational pull on a water strider). I also read that most species of water striders have greasy feet. This would certainly enable them to walk across the water, since oily substances are hydrophobic, and would have a force that naturally repels water away, and vice versa.
4.) Cohesion is the attraction of two like molecules to each other (in this situation, the attraction of water molecules to other water molecules).
5.) A surfactant is a chemical or substance that lowers the surface tension of water. The surfactant (detergent for example) is composed of one part non-polar tail that is hydrophobic --- water-fearing. Because detergent molecules tend to collect at the surface of the water they are mixed with, their non-polar tails stick out of the water because, naturally, they are water fearing. This disrupts the hydrogen bonds at the surface, reducing the surface tension dramatically. (C: Conceptual Physical Science, 1999 p. 443)
Post Questions:
1.) The container with the least surface tension was container D, with the hot H20 and the detergent. This is because the heightened temperature of the water broke some of the hydrogen bonds, causing a decrease in cohesion among the water molecules. The detergent also decreased the surface tension because it disrupted the hydrogen bonds since it is hydrophobic, and the hot water speeded up the mixing in of the detergent.
2.) The container with the greatest surface tension seemed to be container A, with the cold, plain water. Although our results do not directly show this, container one seemed to hold the steadiest, most cohesive water, not only because of its dome-like shape, but also because when we picked it up to dump it into the sink, it spilled less than the others did.
3.) Heat disrupts the hydrogen bonds and breaks them, so there isn’t as much cohesion as there is in a sample of water at a cooler temperature. This is because the hydrogen bonds are more easily maintained in that situation, and therefore there is greater surface tension.
4.) Detergents contain hydrophobic hydrocarbon tails, and a hydrophilic “head” group. This means it is a “surfactant.” When detergent reacts with water, it disrupts the hydrogen bonds, thereby reducing the surface tension of the water.
5.) A dome was able to form on the top of the water containers because the water was piled above the brim of the cup, however the water stuck to itself, and kept from spilling. The hydrogen bonds and the cohesion kept all molecules of water sticking together, and so a dome shape was formed because it was the most favorable shape possible, assuming that the water molecules were all to stay entirely bonded to each other.
Conclusion:
The purpose of this experiment was to see surface tension in action. It provided a visual guide to aid in our understanding of how surface tension works exactly in the real world, and not just in concepts in text books. By completing the experiment, we also learned the conditions under which surface tension is higher or lower.
Our results were significant because they actively portrayed which circumstances support surface tension, and which do not. When we compared cup A, plain cold water, with cup B, water and detergent, cup A seemed to be much stiller, and did not spill, even after 100 paper clips. Although during our experiment cup B did not spill either, it was impossible to move without slopping the soapy water all over the lap table. The same was true for cup C, of hot water; it did not spill after 100 paper clips, but when we so much as touched the rim of the glass, a drop of water ran down the side. It seemed, however, that the detergent cold water spilled more readily than the plain hot water. With cup D, however, the combination of the hot water and the detergent seemed to be what made the water go over the top and spill out with only 91 paper clips.
There were, however, some very prominent sources of error. For one thing, the cups were definitely not filled to an equal height. They looked close, but it is impossible that they were all filled to the exact same caliber. Another source of error was the amount of detergent mixed with the water; because it was difficult to make clear droplets come from the bottle, we tried to just squirt an equal amount into the two cups that required detergent, but this, too, was hard to be perfectly accurate on. Both of these things could have disrupted our data, and lead us toward the wrong conclusion. However, after completing the experiment fairly successfully once, we were able to testify that we think the surface tension is greatest in cooler, purer water, in which there is much opportunity for hydrogen bonding, in contrast to the warm, and/or soapy water. The higher the accommodations for hydrogen bonding cohesion with water molecules, the stronger the surface tension.