Intermolecular Forces Activity
Name
Part 1: The Penny Drop
What effects do intermolecular forces have on surface tension (an inward force that tends to minimize surface area)?
Safety concerns:
Rubbing alcohol is a toxic and flammable. Care should be exercised when using. Goggles should be worn at all times.
Materials:
pennies
water
isopropyl alcohol
Procedure:
1. Place penny face down on the table.
2. Carefully add drops of water on top of the penny. Your goal is to put as many drops on top of the penny
without any water falling onto the table.
3. Count the number of drops that the penny was able to hold. Be sure to observe the penny from the side.
4. Dry the penny and repeat for a total of 4 trials.
5. Repeat the procedure with rubbing alcohol.
Data Table:
Water Drops
Alcohol Drops
Trial 1
Trial 2
Trial 3
Trial 4
Average
Questions:
1. Which liquid had the higher average number of drops?
2. Draw a Lewis Structure for water, H2O, and isopropyl alcohol, C3H7OH.
3. What shape is a water molecule?
4. What intermolecular forces are present in water?
5. What intermolecular forces are present in alcohol?
6. Which liquid, water or alcohol, has STRONGER intermolecular forces? Explain.
7. Why do you think the liquid you chose in the previous question was able to stay on top of the penny better?
Justify your answer in terms of intermolecular forces.
8. Suppose you were doing this experiment with acetone, a liquid that does not have any hydrogen bonding. How
would you expect the result to be in comparison with water and alcohol? Explain.
Part 2: Intermolecular Forces and Evaporation
How does the presence of intermolecular forces affect the rate of evaporation (how fast a substance turns from a liquid
to a vapor) of various liquids?
Safety Concerns:
Hot plates can burn students and isopropyl alcohol is flammable. Care should be exercised and small amounts of alcohol
should be used. Goggles should be worn at all times.
Materials:
Water, olive oil, isopropyl alcohol, acetone, paper towel, hexane
Procedure:
1. Obtain a small piece of paper towel. Place 1 drop each of water, olive oil, acetone, hexane, and isopropyl
alcohol on the paper towel (do not let the drops mix or touch each other). Time how long it takes for each drop
to evaporate. Stop at 5 minutes. Carefully observe any residue from the drops.
Data Table:
Time
Observations
Evaporation Test
Water
Isopropyl Alcohol
Acetone
Olive Oil
Hexane
Questions:
1. Draw Lewis Structures for each of the substances you evaporated. Description: Describe each molecule in terms of
polarity and presence/absence of hydrogen bonding and length of non-polar portion of molecule. What would you
predict about boiling points based on this analysis?
Lewis Dots: Acetone, C3H6O
Description
Lewis Dots: Hexane, C6H14
(the carbons are all bonded
together in a chain)
Description
Lewis Dots: Olive oil: (see teachers
help)
Description