Viscosity, Surface Tension and Temperature (page 3)
Water surface tension= -3.547ln (T) +16.966
Coke surface tension= -2.737ln (T) +14.271
Vinegar surface tension= -2.653ln (T) +13.031
Milk surface tension= -2.237ln (T) +12.561
Water viscosity= -1.1048ln (T) +11.251
Coke viscosity= -0.594ln (T) +10.067
Vinegar viscosity= -0.942ln (T) +11.377
Milk viscosity= -0.637ln (T) +10.407
From 0°C to 100°C Y: viscosity X: surface tension
(Following is a detailed analysis of the significance of what each graph shows.)
According to the graphs, surface tension and viscosity both decrease as the temperature increases. Because as the temperature increases, liquid particles move more rapidly, the particles gain energy from heat by rising temperatures and convert heat into kinetic energy. Also, because of the input of external energy, chemical bonds in liquids are broken; therefore, it is easier for liquid particles to move.
When I look at the graph summarizing the relationship between Temperature and Surface Tension for all liquids, I find out that water supports the most mass, then coke supports the second most mass, then milk supports the third most mass, and vinegar supports the least mass at lower temperatures. Because of strong hydrogen bonds, water supports the most mass. Coke is mostly made up of carbonated water, sugar, caffeine, phosphoric acid, caramel, and natural flavorings. Therefore, there are dipole-dipole forces that are an attractive force between the positive end of one polar molecule and the negative end of another polar molecule and ion- dipole forces that are an attractive force that results from the electrostatic attraction between an ion and a neutral molecule that has a dipole. However, because the solubility of CO2 decreases with the increasing temperature, Coke® would have a stronger dipole-dipole force at lower temperatures than that at higher temperatures. Milk contains significant amounts of saturated fats and proteins. Because fat is polar molecule, there are dipole-dipole forces in milk. Also, milk is a colloid which contains big particles. Therefore, milk supports the third most mass. Vinegar only has dipole-dipole forces and London dispersion forces; therefore, it supports the least mass. But at higher temperatures, milk supports the most mass, Coke® supports the second most mass, then vinegar supports the third most mass, and water supports the least mass. Milk forms a membrane on the surface at higher temperatures, because milk contains proteins, and the proteins would denaturize with the increasing temperature. This is the reason that milk supports the most mass at higher temperatures. Even though, particles in the vinegar move more rapidly with increasing temperature, there are still dipole-dipole forces in the vinegar. However, most of the hydrogen bonds in the water are broken at higher temperatures; therefore, water supports the least mass at higher temperatures.
Milk is a colloid which means molecules in the milk are big particles. Therefore, the viscosity is big. According to the graph summarizing the relationship between Temperature and Viscosity for all liquids, the curve of milk is the least steep. It reveals that the viscosity of milk does not change a lot with increasing temperatures because of its nature—colloid. As the temperature increases, the water molecules move more rapidly; therefore, the hydrogen bonds are being broken. As is shown on the graph, water has a high viscosity at lower temperatures but low viscosity at higher temperatures, because particles gain energy form heat by rising temperatures and become more active. Even though the dipole-dipole forces of vinegar decrease with increasing temperatures, the curve of vinegar is less steep than the curve of water, because the density of vinegar is larger than that of water. The density of vinegar is 1.04 g/cm3, and the density of water is 1 g/cm3.
When I look at the summary graphs, Coke® acts more differently from the other three liquids because of the CO2. The solubility of CO2 decreases with the increasing temperature. At lower temperatures, CO2 dissolves in the water and reacts with the water to form H2CO3 (Carbonic acid); however, the amount of H2CO3 formed is slight. Most of the CO2 dissolves in the water instead of reacting with the water. The dissolved CO2 is attached to H2O by hydrogen bonds. It explains the reason that Coke® supports the second most mass at lower temperatures. At higher temperatures, Coke® still supports the second most mass. Because even though CO2 comes out of solution from Coke® with increasing temperature, there are still dipole-dipole forces and ion-dipole forces. Because there are not many hydrogen bonds created by CO2 and H2O in Coke®, the effect of the disappearance of hydrogen bonds is not significant. The reason Coke® acts differently from the other three liquids is due to the complexity of coke and the presence CO2.
By graphing the relationship between Temperature and Surface Tension and the relationship between Temperature and Viscosity, I obtain the best-fit trend line that shows each liquid’s mathematical relationship between Temperature and Surface tension and Temperature and Flowing time, and then I use the best-fit trend line equations to calculate the equations of each liquid’s surface tension and viscosity. As the surface tension increases, the viscosity increases, because at higher temperatures the surface tension is low, and also, at higher temperatures the viscosity is low. It is based on the concept that particles in liquid gain energy from heat by rising temperatures and convert the energy into kinetic energy. Since the particles have more kinetic energy, they move more rapidly, which weakens the intermolecular force attractions in liquids.
In conclusion, the purpose of my science fair project is to prove that as temperature increases, viscosity and surface tension both decrease, and to determine the relationship between viscosity and surface tension at a constant temperature. My hypothesis, for my science fair project, is that as temperature increases, viscosity and surface tension both decrease. Since viscosity and surface tension are both properties of liquids, there is a relationship between them that surface tension varies directly as viscosity at a constant temperature. My hypothesis was shown to be correct.
However, there are experimental errors and statistical errors in the project. Temperatures I measured are not accurate because the heat transfers to the surroundings; however, I cannot keep the temperature constant because of the limitation of equipments. Also, there are other small experimental errors, such as the measuring time and slight amount of liquid that attaches to the walls of glass cups and of the funnel. I calculate the equations of Surface tension vs. Viscosity for Coke®, water, milk, and vinegar based on the best-fit trend line that I find on the Excel; therefore, there are statistical errors in the equations. However, because of my limited knowledge on the statistics, I do not know how to calculate the statistical errors. If I can find the uncertainty, I will get more accurate and clearer relationship of each liquid’s Surface Tension vs. Viscosity curve. I infer that the sequence of the curves of each liquid’s Surface Tension vs. Viscosity may depend on the densities of each liquid.
If I were to do the project again, in my opinion, it would not change. The data might be slightly different because of experimental and statistical errors. I think the linear relationship between Surface Tension and Viscosity for all four liquids can be verified by doing the project again.
I would like to research the relationship between surface area and surface tension. Also, I want to expand my research to study the relationship between density, viscosity and surface tension at a constant temperature. Then, I would like to construct a general mathematic equation for these three liquid properties for every liquid for a given temperature. As a result, knowing two of these three liquid properties, we can find out the other property, and we can figure out what the temperature is at that time.
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