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 Experiment
5: Grade Level: 1st through 6th
WATER
PURIFICATION BY EVAPORATION AND CONDENSATION
Background
The following demonstration illustrates how the water cycle helps
to purify water. The key terms are evaporation and condensation.
Evaporation is defined as the process through which a liquid becomes
a vapor. Condensation is the process through which a vapor becomes
a liquid, and is the opposite of evaporation. In the case of water,
the main mechanisms for evaporation and condensation are heating
and cooling, respectively.
Materials
Needed
- 4 cups
of dirt or sand
- 1 dozen
stones
- 2 quarts
of water
- 1 large
glass bowl with tall sides (mixing bowl)
- 1 short
glass
- clear plastic
wrap
- a sunny
day
Procedure
Mix the dirt (or sand) and water in a large bowl. Stand a clean
and empty short glass in the center of the bowl. Place the bowl
outside in the sun. Cover the bowl with the plastic wrap and weigh
down the edges with the remaining rocks. Place one rock on the
plastic wrap directly over the cup. Allow the bowl to remain in
the sun for several hours. Look in the cup (it should contain
some relatively clean water free of mud). Look in the bowl (it
should contain the dried dirt).
Follow-Up
Questions
1. What are
the two processes responsible for purifying the water? (Evaporation
and Condensation)
2. Where else do you see condensation? (Cold drink outside on
a hot day)
3. How does this process work on Earth?
4. What is the plastic wrap? (Our atmosphere)
5. What is the condensation? (Clouds and rain)
6. What would happen if the plastic wrap was dirty?
(Air Pollution)
Variations
Add food coloring to water to demonstrate that this process does
not remove all pollutants. This may be done simultaneously with
the procedure above.
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