Lab 10: Evaporation and Intermolecular Attractions

PRELAB: 

DATA:

2. Explain the differences in the difference in temperature of these substances as they evaporated. Explain your results in terms of intermolecular forces.

We know that when the minimum temperature is lower, the substance evaporated more because more energy from the surroundings was put in in order to evaporate it, making the surroundings colder. The substances in order of change from lowest to highest difference are glycerin, n-Butanol, water, ethanol, and methanol. This can be explained by the intermolecular forces in each substance. Glycerin not only has three strong hydrogen bonds, but it is also has a high mass, supporting why it had the lowest change in temperature/evaporated the least/had the strongest intermolecular forces. The temperature change for glycerin is negative because since its bonds are so strong and it is such a large molecule, it actually solidifies instead of evaporating and gives off heat to its surroundings. N-Butanol is also a large molecule, and taking its mass and dipole-dipole bonds into consideration shows why its forces kept it from evaporating much of its substance. Water also had a low difference in maximum and minimum temperatures. Since water only has three atoms and both bonds are strong hydrogen bonds, they take a lot of energy to break. Ethanol had a larger difference in temperature than the previous three substances because it only had one hydrogen bond, and didn't have as much mass as n-Butanol. Methanol had the largest difference in temperatures. This is because it only has one hydrogen bond, and is not as heavy of a molecule as ethanol. In conclusion, much of the difference in temperature depended not only on the amount of hydrogen bonds, which increase intermolecular force, but also on how massive the molecule was, as mass also increases intermolecular forces.

3. Explain the difference in evaporation of methanol, ethanol, and n-Butanol. Explain your results in terms of intermolecular forces.

Since all three substances have the same amount of hydrogen bonds, the difference in evaporation can be explained by the effect of mass on the strength of intermolecular forces. The higher the mass of the molecule, the stronger the bonds, and then the strength of the intermolecular forces increase. N-Butonal is the most massive, explaining its low amount of evaporation (higher temperature = lower evaporation, as explained in the above question). Ethanol has the second highest mass of the three, which is why it evaporated more than N-Butonal but less than methanol. Methanol has the lowest mass of the three, which makes its intermolecular forces less strong, explaining why it evaporated the most.

4. Explain how the number of -OH groups in the substances tested affects the ability of the tested compounds to evaporate. Explain your results in terms of intermolecular forces. 

Since the -OH bonds are very strong hydrogen bonds, they contribute to the strength of intermolecular forces by bonding with oxygens in other molecules, therefore making the intermolecular forces stronger. Making the intermolecular forces stronger means that more energy would be required to break these bonds, which slowed the evaporation rates. Therefore, substances such as glycerin and water with a larger amount of -OH groups would have a smaller change in temperature/evaporate less.

Me and my lab parter with our LabQuest graph-data-collector