Evaporation and CondensationEvaporation and Condensation
A water cycle in a mayonnaise jar-
A model that shows evaporation and condensation at the same time.
Objectives- Students see, relate and understand how water changes through condensation and evaporation.
Prior experience necessary: You will have to prepare them for some time to let them see the connection between the cycle in the jar and the natural cycle. I did this last year with my first grade class in April because it took that long to establish the prior knowledge.
1) Every chance you get, show them that there is usually snow at the top of very tall mountains all year all over the world.
2) Show them several other water, vapor and temperature difference lesson plans.
3) Sometime before making the cyclers, take a bucket of ice out at recess and let the students watch it melt in their hands on a mild or warm day.
4) Every time it's raining I tell my students I know air is rising fast in the sky above us right now because that's how rain happens.
Materials
Ask your school's custodial staff for plastic five gallon buckets. These buckets may make it easier to carry the water and ice to prepare for this lesson. A small cooler might be your preference. Your school should already have a source of very hot water for sanitizing mops. By preparing double the ice and hot water you can choose to let them see the cycle a second time.
1) A bucket of about five pounds of ice.
2) Enough mayonnaise jars for each group of four.
3) Small aluminum "tart" trays with a base large enough to completely cover the mouth of each jar. (from the supermarket baking section)
4) Enough gravel to fill each mayonnaise jar to only the first two inches.
5) About a half gallon of very hot water. (120+ F) You will only need enough to fill the first two inches of each jar. Carry a half gallon at least so that it will stay hot a little longer.
6) A cup that allows you to safely pour the hot water into the jars when the children are sitting in front of it.
WARNING: The students must be very well aware of how to behave in the presence of scalding hot water. This is crucial. Always cover the bucket or container of hot water when not distributing it and keep the kids in their chairs during this time. This model works best when the water is very hot but you alone are responsible for this event. The ice is fun in centers but never the hot water.
Focus
Draw a huge simple picture on the chalkboard of a mountain. Fill in some snow at the peak. Point out to them that it may be comfortable at the base of the mountain but ice cold at the peak at the same moment on the same day.
Model
Stress the safety concerns of spilling the jar and scalding someone else or yourself in the classroom. Stress also that touching the ice with your warm fingers warms and melts it faster and ruins the experiment. Explain and predict what will be observed. We will pour hot water in each jar to cover all the gravel and then put the trays full of ice on top. In about five minutes steam will be rising from the gravel and drops that have condensed under the tart tray will start to "rain" inside the jar. There will be evaporation and rain at the same time for about five more minutes depending on the temperature of water you started with and the amount of ice held by the trays.
Procedure
Fill a tart tray with ice for each group. Fill only the first inch with gravel in each jar. Your materials managers take the jars to the groups. Carefully pour just enough hot water to cover the gravel in each jar. Each group covers their jar with the tray of ice. In less than five minutes changes will appear.
While you are waiting for the vapor to become visible the students get out papers and pencils to prepare to record the event. Write down, discuss and probe for predictions of what will be seen. Draw a before and after version of the jar. When the process begins keep asking students to relate it to a mountain. Have them imagine a mountain in the jar. The peak is cold but the base is hot. Have them compare and contrast the rain condensing under the tray to real rain. Ask them if the rising vapor looks like real fog. This little model truly represents the cycle when considering how many mountain ranges near oceans have vegetation on the seaward side and a desert on the inland side.
Close
Encourage each student to a meaningful reaction or representation in writing. Enter descriptions in your journals. Model writing a letter to a friend in another class that describes what you did and saw. Make a list of things you want to tell your parents tonight about what we saw inside the jars.
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