Lab report / Chem

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A. Student Ms. Macklin May 28, 2020 SCH4U1

Intermolecular Forces Inquiry Lab

Introduction

The structure of a chemical is a very important factor when considering how it interacts with is surroundings. Different structures have different intermolecular forces which are the forces that hold neighbouring particles together within a group of chemicals. The weakest intermolecular force is called the Vander Wall force, which is the attraction between to particles due to instantaneous changes in charge that are caused by elections. Another is called dipole-dipole which is also caused by a permanent imbalance in a molecule due to one chemical having unpaired electrons and therefore a slightly negative charge which will attract the positive charge end of a neighbouring molecule. The final force of attraction are called hydrogen bonds, which occur only in chemicals that have hydrogen and one of nitrogen, oxygen, or fluorine. Many properties of chemicals are caused by intermolecular forces, such as boiling point, state, solubility and evaporation rate. The organic compounds alcohols, alkanes, and ketones have different intermolecular strengths due to having or not having the different types of bonds. Alcohol for example has hydrogen, dipole-dipole and Vander Wall forces, ketones have dipole-dipole interactions and Vander Wall forces, and alkanes have only Vander Wall forces.

In this lab the intermolecular strengths of Vander Walls, dipole-dipole, and hydrogen bonds will be examined by examining different evaporation rates of chemicals with known bond types. This will be done by submerging chromatography paper into varies chemicals for 25 seconds then letting them evaporate into the air for 210 seconds. Chemicals with a stronger intermolecular force, and a greater molar mass will evaporate slower but there will be a greater change of temperature over time. Intermolecular forces have a greater effect of evaporation rate than molar mass. It is predicted that the alcohols will have the greatest change of temperature followed by ketones then alkanes.

Materials

Retort stand

Vernier LabQuest

Ring clamp

Temperature sensor

Elastic band (x9)

5cm chromatography paper (x9)

Gloves

10mL graduated cylinder

Test tube

Stop watch

Watch glass

Goggles

10mL methanol

10mL Acetone

10 mL cyclohexane

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Procedure 1. Attach a test tube clamp to a retort stand, attaching a temperature probe plugged into a Vernier

LabQuest to it. 2. Change the settings of the Vernier LabQuest so that your trial time runs for 210seconds 3. Roll half of a piece of chromatography paper around the temperature probe 4. Pour 10mL of Acetone into the 25mL test tube using a graduated cylinder to measure volume 5. Move the test tube for that the temperature probe is fully submerged for 25seconds 6. Remove the test tube from the temperature probe while simultaneously starting the Vernier

LabQuest and let it run for 210seconds. 7. Record the initial and the final temperature of the temperature probe. 8. Remove the chromatography paper from the temperature probe and dispose the paper and any

remaining acetone in the test tube into the organic waste bin. Wash and dry the temperature probe, and all glassware.

9. Repeat steps 3-8 for the following trials but substitute acetone with cyclohexane and methanol

Observations Table1: Change in temperature of the temperature probe wrapped in chromatography paper which is then soaked in a chemical for 25 seconds and then left in to evaporate for a period of 120s. Refer to Appendix A for raw data of initial and final temperatures.

Chemical Change in Temperature (oC)

Trial 1 Trial 2 Trial 3 Acetone 16.3 17.7 17.5

Cyclohexane 9.7 10.8 12.2 Methanol 17.9 18.4 18.9

Figure1: The average change in temperature of chromatography paper after being submerged in various chemicals for 25 seconds then being left to evaporate for 210seconds

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Discussion In this lab it was expected that the amount of evaporation as shown through change in

temperature increase would occur in chemicals which have more intermolecular forces in play. In this lab there were three possible forces of attraction that can affect the strength of which they are held together. These being Vander Walls, dipole-dipole forces and hydrogen bonding. The first and weakest of the forces being Vander Walls, which affects all molecules. This is caused by the creation of temporary opposite poles at the ends of a molecule caused by the movement of electrons surrounding the atom. As the electrons move around the molecule one side may temporarily have more electrons than the other side. Creating a negative charge on that side. Since one side is now more negative the opposite end becomes more positively charged. If a neighbouring atom also creates negative and positive charges weak temporary attraction between the charged ends exists. The second possible force is a dipole-dipole attraction. This is an electrostatic attraction between the positive end of one molecule and the negative end of another molecule. For example if there is an oxygen atom with a set of unshared electrons then that end is more negatively charged than the other ends of the molecule. Which is in turn attracted the

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positive side of neighbouring molecules. The last force of attraction is hydrogen bonding. Hydrogen bonding is a special case of dipole-dipole attraction. It causes a temporary covalent bond between the hydrogen of one molecule and the nitrogen, oxygen, or fluorine of another molecule. In alcohol this occurs between the oxygen of one molecule and one of the hydrogens in a neighbouring molecule.

Alcohol has all three of these bond types, acetone has two of these bond types and cyclohexane just has one. So it was expected that cyclohexane would have the lowest change in temperature, followed by acetone then butanol, which agrees with the results as can be seen in figure 1. The stronger intermolecular forces had a great temperature decrease over an extended period of time as there bond hold more energy within them, meaning that when they do break apart more energy will be taken away from the chromatography paper, causing the great decrease in temperature. Intermolecular forces play a key role in the effectiveness of perfumes, or other scented beauty products. The product must have a strong odour that is pleasing though not over powering, but also does not evaporate off the wearer in a couple of minutes. At the same time you do not want a product whose intermolecular forces are too strong that no smell can be detected. Chemist continue to find the proper balance of chemicals for a long lasting, pleasing product for people to wear in their everyday lives.

Appendix A: Raw Data Table One: The raw data of the initial and final temperatures of the temperature probe wrapped in chromatography paper which is then soaked in a chemical for 25 seconds and then left in to evaporate for a period of 210s.

Temperature (oC )

Trail 1 Trail 2 Trail 3

Substance Initial End Initial End Initial

Methanol 24.3 6.4 24.4 6.0 23.4

Cyclohexane 24.4 13.5 22.9 13 22.4

Acetone 22.9 6.6 21.8 4.1 23.1