in this activity, the water evaporating inside the jar...saucer transparent jar or cup water salt...

Core Curriculum/Oklahoma 106 © 2006 AIMS Education Foundation

TopicClouds: condensation nuclei

Key QuestionHow does a cloud form?

Learning GoalStudents will observe how water vapor collects on salt grains and make applications to the role of con-densation nuclei in the formation of clouds.

Guiding DocumentsProject 2061 Benchmark• When liquid water disappears, it turns into a gas (vapor)

in the air and can reappear as a liquid when cooled, or as a solid if cooled below the freezing point of water. Clouds and fog are made of tiny droplets of water.

NRC Standard• Clouds, formed by the condensation of water

vapor, affect weather and climate.

Science Earth science meteorology water cycle

Integrated Processes ObservingComparing and contrastingRelating

MaterialsFor each group: black or gray fi lm canister lid waterproof saucer transparent jar or cup water salt hand lens

ManagementSmall groups of two or three allow for closer observation.

Background Information Clouds are formed when water vapor condenses on tiny particles in the atmosphere, called condensation nuclei. Very tiny particles of salt from sea spray, much smaller than the grains of salt being observed, are among the nuclei that collect water. In fact, salt is the primary condensation nuclei in the atmosphere over the oceans. Other nuclei include dust, smoke, volcanic ash, and even pollutants.

In this activity, the water evaporating inside the jar is drawn to the salt grains because salt is hygroscopic. This means it is able to absorb water from the air. The water vapor condenses on the salt and the grains dissolve in the water.

Procedure 1. Have students follow the directions listed on the

task card and discuss the results.2. Encourage students to share cloud experiences

they have had (see Make Your Own Cloud).3. Perform the pint jar activity as students observe. • What do you observe when the balloon skin is

pushed down? [The air in the jar is clearer.] • What do you observe when the balloon skin is

pulled up? [A cloud forms. (As the pressure decreases, evaporation increases. It takes less energy for the water molecules to break free of the surface and become water vapor.)]

• On what kind of particles is the water vapor condensing? [smoke]

Connecting Learning1. How do the salt grains change? [At the beginning,

they are white and almost shaped like a cube. They become more and more transparent. Then they dissolve in the water beads that have formed.]

2. Where did the water come from? [The water from the saucer evaporated into the air inside the cup. Then the salt grains absorbed it.]

3. How is our observation like what happens when clouds form in the atmosphere? [The water vapor in the air collects and condenses on tiny particles of smoke, sea spray (salt), dust, etc.]

4. How is our observation different? [The grains of salt are much, much bigger than the particles around which water condenses in the atmosphere.]

5. Usually we look up at clouds. Have you ever been above a cloud? [in a plane; in the hills, looking down on a foggy valley] Describe your experience.

6. What are you wondering now?


How does a cloud form?

observe how water vapor collects on salt grains and make applications to the role of condensation nuclei in the formationof clouds.

Key Question

Learning Goal


MaterialsFor each group: black or gray fi lm canister lid saucer transparent jar or cup water salt hand lens

MaterialsFor each group: black or gray fi lm canister lid saucer transparent jar or cup water salt hand lens

Directions1. Sprinkle a few grains of salt in the lid so they do not touch each other.2. Pour just enough water to cover the bottom of the saucer.3. Place the lid in the saucer, being careful not to get water inside the lid. 4. Observe the salt with the hand lens. Cover the lid with the jar or cup. 5. Observe every 30 minutes for a couple of hours, then again 24 hours later.6. Write or draw observations in your journal or on another piece of paper.7. Relate observations to the tiny particles around which clouds form in the atmosphere.

Directions1. Sprinkle a few grains of salt in the lid so they do not touch each other.2. Pour just enough water to cover the bottom of the saucer.3. Place the lid in the saucer, being careful not to get water inside the lid. 4. Observe the salt with the hand lens. Cover the lid with the jar or cup. 5. Observe every 30 minutes for a couple of hours, then again 24 hours later.6. Write or draw observations in your journal or on another piece of paper.7. Relate observations to the tiny particles around which clouds form in the atmosphere.

38


When it is hot...

When it is cold...

In a pint jar...

(Have an adult demonstrate.)1. Cut off the neck of a 9-inch balloon. Stretch the remaining skin over the glass pint

jar to make sure it fi ts. Remove the skin.2. Fill the jar about 2 cm deep with hot water. Swish the water around the jar to warm

the sides. Pour out all but a small amount, 15 mL (1 tablespoon) or so.3. Light a match and drop it into the jar.4. Quickly cover the jar with the balloon skin. Put a piece of dark

construction paper behind the jar for contrasting background.5. Push against the balloon skin. Then pull on the balloon skin.

What do you observe?


1. How do the salt grains change?

2. Where did the water come from?

3. How is our observation like what happens when clouds form in the atmosphere?

4. How is our observation different?

5. Usually we look up at clouds. Have you ever been above a cloud? Describe your experience.

6. What are you wondering now?

Connecting Learning