Lab 15
Evaporation and Intermolecular Attractions Lab
Shiva Senthil
7/30/17
Introduction
The purpose of this lab was to observe how intermolecular attractions affect the evaporation of different substances. The lab consisted of placing temperature probes in a substance and then pulling it out and observing how the temperature changed over a 240 second period.
Data
Questions
2. Explain the differences in the difference in temperature of these substances as they evaporated. Explain your results in terms of intermolecular forces.
The two factors that affected the difference in temperature were the strength of the intermolecular forces and the molar mass of the substance; however, the intermolecular force was the more important factor. Although all five tested substances had hydrogen bonding as one of their intermolecular forces, the strengths of the hydrogen bonding varied. The stronger the hydrogen bonding, the less likely the substance evaporated, which meant the temperature went up or only went down a little bit. This is because the substance was more likely to absorb energy from the surrounding air rather than evaporate and release the energy as the bonds were so strong. Glycerin, which had the strongest hydrogen bonds, was the only substance that increased in temperature. Methanol, ethanol, and n-Butanol, which had the weakest hydrogen bonds, saw significant decreases in temperature. The other factor, which only applied if the hydrogen bonds were the same strength, was molar mass. A higher molar mass meant that more energy was needed to cause the substance to evaporate. Of the three substances with the weakest molar masses, n-Butanol had the highest molar mass and thus had the smallest temperature decrease. Methanol had the lowest and saw the largest temperature decrease.
3. Explain the difference in evaporation of any two compounds that have similar molar masses. Explain your results in terms of intermolecular forces.
If two compounds had similar molar masses, the compound with the greater intermolecular forces would evaporate less because more energy would be needed to break the forces. Glycerin and n-Butanol had somewhat similar molar masses, but glycerin had stronger hydrogen bonds. Thus, glycerin evaporated less, and absorbed more energy, with an increase in temperature. N-Butanol evaporated more because its bonds were easier to break, resulting in a significant drop in temperature.
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.
A greater number of OH groups means the hydrogen bonds are stronger. There is more opportunity for hydrogen bonding to occur as there are more very positive hydrogen atoms and very negative oxygen atoms. Glycerin had most OH groups (three) and thus the strongest hydrogen bonds. As hydrogen bonds are the greatest intermolecular force, glycerin had the greatest intermolecular forces overall. Glycerin was the only substance whose temperature actually increased. Water had two OH groups, and had the smallest decrease in temperature. Methanol, ethanol, and n-Butanol all had only one OH group. These substances had temperature changes correlating to their molar masses.
Data
Table with Lewis structure, molar mass, intermolecular forces
Table with temperature readings 240 seconds apart
Questions
2. Explain the differences in the difference in temperature of these substances as they evaporated. Explain your results in terms of intermolecular forces.
The two factors that affected the difference in temperature were the strength of the intermolecular forces and the molar mass of the substance; however, the intermolecular force was the more important factor. Although all five tested substances had hydrogen bonding as one of their intermolecular forces, the strengths of the hydrogen bonding varied. The stronger the hydrogen bonding, the less likely the substance evaporated, which meant the temperature went up or only went down a little bit. This is because the substance was more likely to absorb energy from the surrounding air rather than evaporate and release the energy as the bonds were so strong. Glycerin, which had the strongest hydrogen bonds, was the only substance that increased in temperature. Methanol, ethanol, and n-Butanol, which had the weakest hydrogen bonds, saw significant decreases in temperature. The other factor, which only applied if the hydrogen bonds were the same strength, was molar mass. A higher molar mass meant that more energy was needed to cause the substance to evaporate. Of the three substances with the weakest molar masses, n-Butanol had the highest molar mass and thus had the smallest temperature decrease. Methanol had the lowest and saw the largest temperature decrease.
3. Explain the difference in evaporation of any two compounds that have similar molar masses. Explain your results in terms of intermolecular forces.
If two compounds had similar molar masses, the compound with the greater intermolecular forces would evaporate less because more energy would be needed to break the forces. Glycerin and n-Butanol had somewhat similar molar masses, but glycerin had stronger hydrogen bonds. Thus, glycerin evaporated less, and absorbed more energy, with an increase in temperature. N-Butanol evaporated more because its bonds were easier to break, resulting in a significant drop in temperature.
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.
A greater number of OH groups means the hydrogen bonds are stronger. There is more opportunity for hydrogen bonding to occur as there are more very positive hydrogen atoms and very negative oxygen atoms. Glycerin had most OH groups (three) and thus the strongest hydrogen bonds. As hydrogen bonds are the greatest intermolecular force, glycerin had the greatest intermolecular forces overall. Glycerin was the only substance whose temperature actually increased. Water had two OH groups, and had the smallest decrease in temperature. Methanol, ethanol, and n-Butanol all had only one OH group. These substances had temperature changes correlating to their molar masses.
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