Activity 2: Hydrologic Cycle

WATER: AMAZING AND PHASING

Summary:

Water comes in three different phases which play a very important part in the hydrologic cycle. Activities demonstrate changes that take place as water passes through each of the phases.

Instructional Method: Experiment

Goal: To show students how water passes through phases.

Objectives: Students will be able to:

• List and describe the three phases of water: water, ice, vapor (steam).
• Label the basic hydrologic cycle, using a copy of the master cycle.
• Identify the temperature at which water boils based on their own observations with a Celsius thermometer.
• Describe how water, in all three phases, is used in the world.

Time:

Set up: 20 min.
Experiment: 45 min.
Discussion: 20 min.

Materials Needed:

• Two 250 ml flasks
• Two rubber stoppers with tubes and hole for thermometer
• Plastic clear tubing
• Hot plate
• Graduated cylinder
• Two thermometers (Celsius)
• Two rulers (metric)
• Marker
• Ice cubes
• Pan of water
• PDF water cycle

Vocabulary:

boil
condense
freeze
gas
liquid
melt
phase
solid
steam
sublimation
vapor

Background:

The three phases of water include: liquid, solid ice, and gaseous vapor. One drop of water can change into each of these phases perpetually, without losing or gaining any mass.

Freezing is the act of water changing from a liquid to a solid (ice). Melting is the act of ice changing into liquid water. Boiling is the act of water changing from liquid into vapor. Condensation is the act of water vapor changing into a liquid.

Phase changes often are associated with either a boiling point or a freezing point. Boiling point is the temperature at which a liquid actively changes into a vapor. The boiling point of water is 212°F (100°C). Freezing point is the temperature at which a liquid is actively changed into a solid. The freezing point of water is 32°F (0°C). If water vapor is cooled below the boiling point, it condenses and goes back to its liquid form. If ice is warmed above the freezing point, it melts and changes into its liquid form. If you continue to warm liquid from melting ice it eventually reaches its boiling point and changes into vapor.

Older students may also want to explore the idea of sublimation, the act of a solid changing directly into vapor without going through the liquid phase. On sunny winter days, sublimation is visible as snow disappears without making the sidewalk wet.

In this activity we will explore the three basic phases of water and try to predict the boiling and freezing points based on observations and temperature readings.

Instructional Procedures:

Part I: Liquid and Vapor

1. Place two beakers on the table and put an equal volume of water in each. Make a list with students describing the differences and similarities of the two containers of liquid.
2. Set up the lab equipment according to the diagram. Pour 150 ml water into a flask, and place it on the hot plate. Mark water depth on the side of the flask with a wax crayon.
3. Secure thermometers in the rubber stoppers, and place stoppers into the tops of both flasks.
4. Place ice cubes in a pan of water and set the empty flask into it. The two flasks should sit at the same height above the table. Use books or blocks to raise the empty flask in its water bath if necessary.
5. Turn on the hot plate.
6. Have students observe what is happening, and take notes on the behavior of the water and the temperature in the flasks, marking the depth of the water in both flasks every 5 minutes. Note: As water boils, it will turn into a gas called water vapor, and rise into the tubing. As molecules move towards the cold flask, water condenses in the tubing and drips into the empty flask.
7. Have students record the temperatures and depths of the condensed water in the second flask.

Discussion:

Where did the water in the cold flask come from? How did it get there? Which two phases of water did we see? What does it mean to boil? What does it mean to condense? What is the third phase of water?

Part II: Liquid and Solid

1. Allow all the water to be collected into one flask.
2. Remove flexible tubing from the stopper, and mark the depth of the water with a third color marker. (Make it very clear).
3. Place the flask in the freezer.
4. Have the students observe the flask every 15 minutes, recording temperature and any other observations, until the water is completely frozen. Note: the time frame on this activity may have to be adjusted or consider using an insulated container of dry ice to freeze the water faster.
5. Once the water is frozen, mark the new depth of the water. Take the flask out and discuss the properties of a solid, including the expansion of water as it freezes.
6. Continue observing the flask at room temperature, until it is in a liquid state again.
7. Feel free to repeat Activity 1A again, using the same water.

Discussion:

What happened to the water? What does it mean to freeze? Why was the water deeper when it was frozen than when it was liquid? When do we see solid water in nature? What happens to solid water in nature? Do oceans boil? Can water be changed into a vapor without boiling first? Where do we see phase changes in the hydrologic cycle? How do we know when water changes phases in the hydrologic cycle?

Included National Parks and other sites:

Death Valley National Park
Everglades National Park
Yellowstone National Park

Photos:

Death Valley Stream
Old Faithful Geiser

Utah Science Core:

1st Grade Standard 2 Objective 1
1st Grade Standard 3 Objective 1,2
2nd Grade Standard 2 Objective 1,2
5th Grade Standard 1 Objective 2

 

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