Lesson: Condensation

Prerequisites:

• The Water Cycle
• Evaporation

Objectives:

1. To demonstrate the concept of condensation

Materials:

• Glass Cups or Jars
• Ice Cubes
• Water
• Paper Clips
• 8-10 Petri Dishes or similar shallow plates
• 4-5 tin lids
• Salt

Introduction:

• What are clouds?
• How are they made?
• Have you ever seen a cloud close to the ground?
• What is that called? (fog)
• How is fog made?
• In the winter, when you walk outside, what happens to your breath when it hits the cold air?

Body:

Have the students fill their cups with ice. Add cold water to everyone's cup. Ask: "Do the cups feel wet or dry? Do the cups feel hot or cold?"

Let the cups sit for about one half hour. Ask: "What do you notice about the outside of your cups? Are they wet or dry? Where did the water come from? (teacher may need to direct the students towards the idea that the water came from the air.) Students can leave the ice water glasses out overnight or for several hours. If the class has studied evaporation, then discuss with them what happened to the water on the outside of the glass. If necessary refer to the evaporation lesson.

Now divide the class into four or five groups. Each group should get two petri dishes, two paper clips and one tin lid. Ask a member of each group to place the paper clips in one of the petri dishes, then set the tin lid on top of the paper clips. Have another group member give one shake of the salt shaker, or whatever it takes to get 6-10 salt crystals on the tin lid. Then the teacher will pour a thin layer of water into each petri dish so the tin lid doesn't get wet any water on it.

Now a member from each group should place an empty petri dish on top of each set up - careful to not bump any water onto the tin lid. (Could also use plastic wrap or some other clear cover.)

Let the set up sit for about one half hour. Ask for predictions from students of what they think might happen. Have one group member be a recorder and record what they see happening. (Eventuallly water from the dish will collect of condense around the salt crystals leaving little drops of salt water on the tin lid.) Ask: "What happened to the salt? Why are there drops on the lid instead of salt?"

Explain that the water evaporated from the dish and created air that had high humidity in the dish. Water from in the air collected around each salt crystal until the salt dissolved or melted. Now, all that is left are small drops of salty water on the tin lid. This process is called condensation. This is the same thing that happens in clouds before it rains. (Students may ask where the salt comes from or how does the salt get into the sky.) Explain that condensation can happen around other small particles like dust and that salt can get in the sky from the evaporation of ocean spray.

Each group can now take the lid off their set up and make predictions about what they think might happen to the drops. (After about half an hour, the water will evaporate and only salt will be left.) Ask the students to observe what they see on their lid. (They can taste it to discover that it is salt that is left.

If the class has already studied evaporation, then review what happened to the water. If they haven't, then this may make a great introduction.

Conclusion:

Vocabulary Words:

• condensation
• evaporation

Evaluation:

Followup Lessons:

• Precipitation

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