Evaporation - Intermolecular Forces PDF

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This experiment investigates intermolecular forces and the effect they have on evaporation. This report gives substantial understanding and background of what intermolecular forces are in chemistry and how they are applied in regular life. ...

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SCH4U October 24th, 2017 The Effect Intermolecular Forces have on Temperature Change due to Evaporation Introduction: This experiment will investigate the impact intermolecular forces have on the interaction of the molecule with its surroundings. A molecule is a substance that has two or more different atoms bonded together. The forces that bind the atoms together in the molecule are referred to as intermolecular forces. There are 3 main kinds of intermolecular forces; dipole-dipole, the strongest intermolecular force, Van der Waal bonds, the weakest intermolecular force and hydrogen bonds, the second strongest force. Dipole-dipole bonds only occur in molecules that are polar in nature. A molecule that is polar has an area of the molecule that more negative electrons are drawn to, creating poles in the molecule that allow one part of the molecule to be positively charged, and one side of the molecule to be negatively charged. The positive and negative ends are attracted to each other, known as a dipole-dipole force. This creates a molecule that requires a lot of energy to break and manipulate. Van der Waal bonds occur in molecules that are polar and nonpolar in nature, however polar molecules are bound by both Van der Waal forces and dipole-dipole forces, and nonpolar molecules are only bound by Van der Waal forces. Nonpolar molecules have every part of the molecule equal in charge, and therefore there are no parts of the molecule attracted to one another. Van der Waal bonds occur due to instantaneous charge imbalances in a molecule. As the electrons orbit the various atoms in the molecule, sides of the molecule can have more or less electrons at any given time, creating temporary poles that allow the molecule to be attracted to itself. Since there are no permanent poles, the forces that hold nonpolar molecules together are easy to break and manipulate. As the molecule gets bigger, the amount of electrons increases, and therefore there are more instantaneous charge imbalances, creating stronger Van der Waal bonds that are slightly more difficult to manipulate and break. Hydrogen bonding occurs in molecules that contain a hydrogen and a highly electronegative atom. These bonds can occur intermolecularly and intramolecularly, and are stronger than Van der Waal forces, but not as strong as dipole-dipole forces. Molecules that contain hydrogen bonds will be more difficult to break and manipulate than molecules with just Van der Waal forces. Through evaporation, the characteristics of these bonds types can be observed. Evaporation is a process that requires energy. When a liquid substance evaporates into the atmosphere, it pulls heat energy from its surroundings in order to complete the process. The stronger the molecular bonds, the more heat energy the evaporation of the molecule will require. In this lab, the known intermolecular forces in substances water, butan-1-ol, and octan-1-ol will be examined through evaporation. A thermometer will be placed on a cotton ball, and then the substance will be added to the cotton ball and left to evaporate for three minutes. The lowest temperature that occurs in the three minutes will be compared to the initial temperature to determine how much heat energy the substance acquired from the atmosphere in order to evaporate. It is anticipated that molecules with stronger known intermolecular forces, water and octan-1-ol will have a more drastic temperature change than that of molecules with

weaker intermolecular force, butan-1-ol. Butan-1-ol is predicted to have the lowest change in temperature because it has less Van der Waal bonds than octan-1-ol, and no hydrogen bonds like water. Materials: temperature probe stopwatch Vernier attachment water 9x cotton balls 3x droppers 3x 50mL beakers Procedure: 1) Obtain 15mL of water in a 50mL beaker. Set up temperature probe to Vernier attachment. 2) Put one unused cotton ball on end of probe. Wait 30 seconds and then record initial temperature of cotton ball. 3) Using dropper, put 25 drops of water on to cotton ball. Wait 5 minutes. Record lowest temperature of cotton ball. Remove cotton ball and wipe off probe. Dispose of cotton ball in the organic waste bucket. 4) Repeat steps 1-3 two times. 5) Repeat steps 1-4, substituting water for butan-1-ol and octan-1-ol Observations: Table 1: The Temperature Decrease of the Cotton Ball Observed due to Evaporation of the Added Substance after 3 Minutes Temperature Decrease (

)

Substance ordered by Strength of Intermolecular Bond

Trial One

Trial Two

Trial Three

Average

Water

-2.2

-5.1

-5.1

-4.1

Octan-1-ol

-1.1

-1.7

-2.1

-1.6

Butan-1-ol

-0.3

-1.7

-1.5

-1.2

Figure 1: The Average Temperature Decrease of the Cotton Ball due to Evaporation of the Added Substance After 3 Minutes Discussion: The purpose of this experiment was to investigate the effect intermolecular forces have on the molecules interaction with its environment. This was examined through the evaporation process of three different molecules with known bonding forces, water, butan-1-ol, and octan-1-ol. Small amounts of each were added to cotton balls with an attached thermometer, and left for three minutes. The lowest temperature that occurred in those three minutes was compared with the initial temperature to determine the heat energy taken from the environment, as evaporation is an endothermic process. It was predicted that the molecules with stronger intermolecular forces, water and octan-1-ol would require more heat energy to evaporate than molecules with weaker intermolecular forces, butan-1-ol. The lab proved the hypothesis was correct, as butan-1-ol had the smallest temperature decrease, meaning that it took the least heat energy from the environment to evaporate, and water had the largest temperature decrease, meaning it took the most heat to from the environment to evaporate, as seen in Figure 1. Water took the most heat energy to evaporate. Water is a molecule that consists of two hydrogens and one oxygen, and is polar in nature. This means the molecule is bonded together by Van der Waal forces, dipole-dipole forces and hydrogen bonds. Due to water having three types of bonds holding the molecule together, the molecule is very hard to manipulate and break. This also means water will require more energy to change into a gaseous form. This is why water took the most heat energy to evaporate, and had the largest temperature decrease, as shown in Figure 1. Octan-1-ol and Butan-1-ol are both organic compounds, known as alcohols, and share very similar properties. The hydroxide on the first carbon of the chain creates a negative end on the molecule, making it polar in nature. Since octan-1-ol and butan-1-ol are polar, they are

bound together by both dipole-dipole and Van der Waal forces. The difference between octan-1-ol and butan-1-ol is the size of the molecule. Octan-1-ol is larger than butan-1-ol, and therefore has more electrons causing instantaneous charge imbalance to occur more often. This creates stronger Van der Waal bonds, resulting in octan-1-ol being a molecule that is harder to break, manipulate and change into a gaseous form than butan-1-ol, despite how similar the two alcohols are. This explains why in Figure 1, a bigger temperature decrease was observed in the evaporation of octan-1-ol. Octan-1-ol required more energy than butan-1-ol to evaporate solely due to stronger Van der Waal bonds. Intermolecular bonds greatly affect how a molecule interacts with its surroundings. In the endothermic process of evaporation, stronger intermolecular forces in a molecule cause the molecule to need more heat energy to evaporate than that of molecules with weaker intermolecular forces. Evaporation is a crucial process for water cycle on Earth. Water evaporates from bodies of water on the surface of the planet, into the atmosphere, to then turn into precipitate and return to the surface again. Without evaporation, there would be no rain, and all water would be contaminated. When the water evaporates, it often leaves behind unwanted minerals and substances that contaminate the water. These substances are often left behind because they have stronger intermolecular forces than water, and therefore do not receive enough heat energy from the environment to evaporate and stay with the water.

Appendix A: Calculation used to calculate average for Table 1:...