BioEd Online

Teacher Background

Water is one of the few substances that can be found in all three states—solid, liquid and gas—at any given time somewhere on Earth. For example, snow and ice always are present at the poles, as well as on the tops of high mountains. Liquid water is abundant in many places on Earth, including lakes, rivers, oceans and underground. Water vapor, the gas phase of water, usually makes up a small component of the air around us (up to 5%), and can be observed as steam when liquid water is heated.

When talking about this important resource, we usually think of liquid water. However, if water were not continuously cycling among its three states, the world’s stores of freshwater quickly would become depleted or too polluted to use. Fortunately, our supply of freshwater continually is collected, purified and redistributed as part of the water cycle. Also known as the hydrologic cycle, this continuous process replenishes our water sources through precipitation (rain, mist, snow and sleet, for example). Some water from precipitation soaks into the ground. The rest runs off into streams, lakes and the oceans. Heat from the sun causes water to evaporate from the land and from bodies of water. Water vapor collects in the atmosphere until there is too much for the air to hold in clouds, leading once again to rain or snow.

This activity allows students to explore properties of water that are important to the water cycle.

Objectives and Standards

Concepts

• Water can be found naturally as a solid, a liquid and a gas on Earth.

• Water circulates among these three states in the water cycle.

Science, Health and Math Skills

• Predicting

• Making and recording observations

• Measuring

• Drawing conclusions

Materials and Setup

Materials per Group of Students

• 20 ice cubes

• 2 cups of sand

• Shoebox (see SETUP for alternative)

• Aluminum foil (to line the bottom and sides of the shoebox)

• Plastic wrap (to cover the top of the shoebox)

• Large rubber band, about 7 in. x 1/8 in. (to secure the plastic wrap)

• Measuring cup, 8 oz

• Lamp with incandescent bulb if sunny window is not available

• Copy of “The Water Cycle” page

• Each student will need:

• Sheet of drawing paper

Setup

1. Place a container of sand in a central area, so that groups may measure out the quantities they need.

2. As an alternative to shoe-boxes, aluminum foil and plastic wrap, students may use plastic boxes with clear covers.

3. Have students work in groups of four.

Procedure and Extensions

Session 1: Making the model

1. Have each group line the inside of its box by pressing a single sheet of aluminum foil along the bottom and up the sides of the box.

2. Direct groups to take turns measuring out two cups of sand and placing it in a pile at one end of their boxes.

3. Instruct each group smooth the sand to create a hill at one end of the box, gradually sloping it toward the other end. This will form the “land” in the model.

4. Have each group place 20 ice cubes on top of the “land” in the box. The ice cubes will represent “snow” and “ice” in the model.

5. Help the groups cover each box with a sheet of clear plastic wrap and secure it with a large rubber band. (If using plastic storage boxes, cover them securely.)

6. Discuss the models with the class. Ask, Which part of the box and its contents could represent land? Which part could represent snow on the tops of mountains or ice in the winter? Do you think a lake could form? If so, where would it be?

7. Ask students, What do you think will happen if we put the boxes in the sun? Have each student fold a sheet of drawing paper in half. Then direct students to use one-half of the sheet to draw a “side view” of what they think the box will look like at the end of the day.

8. Place the boxes in a sunny window or a under a lamp with an incandescent (not fluorescent) light bulb. If possible, have the students observe their boxes at intervals throughout the day. Otherwise, have them observe the boxes within the next day or so.

Session 2: Looking at results

1. Have the students observe their boxes without removing the covers. Prompt them to note the changes that have occurred inside the boxes and ask, What happened to the ice cubes? What else is different about the inside of the box? In most cases, at least a few drops of water will have condensed on the inside of the covering. Ask, Where did the drops of water come from?

2. Help students understand that all three states of water have been present in their shoeboxes. Review the different states in which water can be found—ice or snow (solid), liquid water and water vapor. Breathe on a mirror or piece of glass to show students how water vapor condenses on a surface, OR boil a small container of water, so that students may observe the cloud of steam. Hold a glass or mirror above the steam.

3. Let the students remove the covers from their boxes. Tell them to observe the surface of the sand and ask, Has the surface of the sand changed? In what ways?

4. Talk about where the water in the box has gone. Ask, Where was all of the water in the box when we started? Where is the water now? If students have not noticed that the surface of the sand is wet, point out that some of the water has run into the bottom of the box to make a “lake,” and some has soaked into the sand. Help students understand that the same processes take place outside when it rains and snows.

5. Have students draw a side view of the box on the remaining half of their folded sheet of drawing paper. Discuss the outcomes they observed and compare their findings with their predictions.

6. Challenge students to think about what would happen if other substances (for example, chemicals, oils, etc.) also were present on or in the sand.

7. Give each student a copy of “The Water Cycle” page, and/or project an overhead transparency of the page. Have students identify the forms in which water is present in the diagram (for example, snow on mountaintops is a solid form of water, and water evaporating from the ocean represents water in a gas phase). Direct very young students to place a sticker everywhere on the page where they can find some form of water.

Extensions

• Have students design experiments to learn what happens to chemicals in soil by placing drops of food coloring on the sand in the shoeboxes before adding the ice cubes. Ask students to note where the colors end up in the system.

• A limited version of this activity can be conducted using plastic resealable bags. Add small amounts of sand and ice to each bag, then tape the bags to a window.

• Provide an opportunity for students to observe water transport within plants. Place a stalk of celery in a container of water with a few drops of food coloring. The colored water will travel up through the water-conducting tissue in the stalk into the leaves.

Handouts and Downloads