How can you extract water from the air?

• 1 temperature sensor
• 1 relative humidity sensor
  Note: if a relative humidity sensor is not available, refer to the Relative Humidity Measurement activity, which explains how to use the temperature sensor to measure relative humidity.
• 1 piece of tin foil — 4 cm x 4 cm
• 1 plastic container
• cup of warm water
• cup of ice cold water

This activity addresses NSES standards for earth and space science and inquiry at grades 5-8 for structure of the earth system
(http://books.nap.edu/readingroom/books/nses/6d.html#es).

There are no special safety concerns in this investigation.

1. Using what you have learned about dew point, you are going to create a situation where dew forms in your classroom. Obtain a container.

2. Fill the container with only enough warm water to cover the bottom.

3. Take a piece of tin foil and lightly bend up the edges so that the foil can float on the water in your container. Put the tin foil on the water.

4. Measure the classroom temperature and relative humidity, if you haven’t just done so (see activities Relative Humidity Measurement and Water in the Air: Trial 2).

Relative humidity (%)=

Temperature (degrees C)=

5. Using the water density chart below, what is the dew point for this temperature and relative humidity? You can use the ruler tool to read values on the graph. See Technical Hints for using the Ruler Tool.

Classroom dew point temperature (degrees C)=

6. You can chill the water and the tin foil in your container by carefully adding ice-cold water. If you wanted to create a situation where dew forms on the tin foil and you use the smallest amount of cold water possible, how would you do it? Get together with your group members and design a method. Describe your method below. Be prepared to share your method with the class.

7. Once your teacher approves your method, create dew on the tin foil. Use the temperature sensor to measure the temperature of the water. Refer to Technical Hints to connect the temperature sensor. Refer to Technical Hints to record a single measurement. You will know when dew forms because the tin foil will look slightly “foggy.” What temperature is the water when dew forms?

Water temperature (degrees C)=

1. How does your observed water temperature that causes visible “dew” on the aluminum foil compare with the calculated dew point temperature?
2. If they are different, why might this be so?
3. Suppose you want to fill the room with fog. How might you do this?

Describe other situations in nature that are like what you did in your classroom. In each case, describe what causes a temperature drop that results in dew or fog.

Research the question: Does water evaporate in space?