Activity 6.
3
Condensation
Does cooling water vapor increase the rate of condensation?
In the previous activity, students design and conduct experiments and see that heating water increases
the rate of evaporation. In this activity, students explore the reverse process—condensation. After
seeing water vapor condense, students will help design a test to see if cooling water vapor has an
effect on the rate of condensation.
Materials needed for each group
Hot tap water
Cold water
Ice cubes
3 Tall clear plastic cups
3 Wide clear plastic cups
Magnifier
Paper towels
Notes about the materials
● Be sure you and the students wear properly fitting goggles.
● Hot tap water is sufficiently hot for the activity. Students should use care
when handling hot tap water.
● This activity calls for both tall and wide clear plastic cups. Be sure the cups fit
together as shown.
Activity sheet
Copy Activity sheet 6.3—Condensation, pp. 353–354, and distribute one per student
when specified in the activity.
Assessment
An assessment rubric for evaluating student progress during this activity is on pp. 372–373. For this
formative assessment, check a box beside each aspect of the activity to indicate the level of student
progress. Evaluate overall progress for the activity by circling either “Good”, “Satisfactory”, or
“Needs Improvement”.
350 Investigation 6. States of matter © 2007 American Chemical Society
Activity 6.3
Condensation
Question to investigate
Does cooling water vapor increase the rate of condensation?
1. Discuss with students some of their own experiences with condensation.
Ask students about their experiences with condensation using questions such as the following:
● Did you ever notice that if you have a cold drink on a humid day, the outside of the cup or can gets wet?
● Where do you think this moisture comes from?
● You may have made a cold window “cloudy” by breathing on it and then drawn on the window
with your finger. Where do you think that cloudiness comes from?
● A cloud is made up of tiny droplets of water. Where do you think they come from?
Help students realize that the moisture in all of these examples came from water vapor in the air. Remind
students that water vapor is one of the gases that makes up air.
Distribute Activity sheet 6.3—Condensation and have students list two examples of tiny drops
of water appearing on a cold surface.
2. Have students conduct an experiment to observe the process of condensation.
Procedure
1. Fill a wide clear plastic cup about 2/3 full of hot tap water. Place a taller clear plastic cup (with a
smaller rim) over the top as shown.
2. Watch the cups for 1–2 minutes.
3. Use a magnifier to look at the sides and top of the top cup.
4. Take the top cup off and feel the inside surface.
Expected results: The top cup will become cloudy-looking as small drops of liquid
water collect on the inside surface of the cup.
3. Discuss with students what they think is happening inside the cups.
Ask students questions like the following:
● What do you notice about the top cup?
● What do you think is on the inside of the top cup?
● Do you think that some of the water from the bottom cup is evaporating?
● Would you expect there to be more water vapor in the air inside the cups or outside the cups in
the classroom air?
● How do you think the drops of water on the inside of the top cup got there?
● When water changes from a liquid to the gas water vapor, we say that it evaporates. Since conden-
sation is the opposite of evaporation, explain what changes take place when water condenses.
© 2007 American Chemical Society Investigation 6. States of matter 351
Students should agree that the inside of the top cup is coated with tiny drops of liquid water. Since students
saw in the last activity that heating water increases the rate of evaporation, they should realize that some of
the hot water must have been evaporating pretty quickly, filling the air inside the cups with the gas water
vapor. As water vapor moves away from the hot water it cools. It also cools when it comes in contact with
the inside surface of the top cup. When the water vapor cools enough, it changes state, becoming tiny drops
of liquid water. The process of changing from a gas to a liquid is called condensation.
4. As a class, discuss an experimental design that could investigate whether cooling
water vapor increases the rate of condensation.
Remind students that they discovered that heating water increases the rate of evaporation. Now ask them
if they think the reverse is true: Does cooling water vapor increase the rate of condensation?
Ask questions such as the following so that students better understand the experimental design described
in the procedure below:
● We will need some water vapor in this experiment. How can we get some?
● How will we cool the water vapor?
● Will we need more than one sample of water vapor?
● Should we cool one sample of water vapor, but not the other?
Students may suggest collecting water vapor as described on the previous page or collecting it over a pot
of boiling water. Students may have many ideas for cooling water vapor, like using ice, placing a sample
in a refrigerator or cooler filled with ice, or placing a sample of water vapor outside if the weather is cool
enough. Students should realize that they will need 2 samples of water vapor, one of which is cooled. By
comparing the size of the drops in both samples, students can determine whether cooling water vapor
increases the rate of condensation.
5. Have students do an activity to find out whether cooling water vapor increases the
rate of condensation.
Procedure
1. Fill two wide clear plastic cups about 2/3 full of hot tap water.
2. Quickly place taller clear plastic cups (with smaller rims) upside down
on each cup, as shown.
3. Place a piece of ice on top of one of the cups.
4. Wait 2–3 minutes.
5. Remove the ice and dry the place where the ice was with a paper towel. Hot Hot
tap water tap water
6. Use a magnifier to examine the tops of the two upper cups.
Expected results: There will be bigger drops of water on the top of the cup with ice.
6. Discuss students’ observations and draw conclusions.
Ask students questions such as the following:
● Which top cup appears to have more water on it?
● What does the amount of water have to do with the rate of condensation?
● Does cooling water vapor increase the rate of condensation?
Students should realize that the bigger drops on the cold top cup indicate a greater amount of water and
therefore more condensation. Because the water vapor in both sets of cups was condensing for the same length
of time, the water vapor in the cooler top cup must have condensed at a faster rate.
352 Investigation 6. States of matter © 2007 American Chemical Society
