My Science Box

Lesson Plan
Optional mini-exploration:

1. Ask students what they predict will happen if I zip an ice cube in a Ziplock bag. In particular, what will happen to the weight of the bag as the ice turns to water and then turns to water vapor? Many students will think that the bag will weigh less after the water melts and some of it turns to water vapor.
2. Have students write down their predictions on a lab notebook. I had my students draw a series of pictures with captions showing the plastic bag now, in 2 hours, and tomorrow.
3. Try the experiment. Pass out bags, sample cups and ice cubes. Place the ice cube in the sample cup and then place the whole thing in the Ziplock bag. Make sure there is a good quantity of air in the bags before sealing them so that any condensation that accumulates may be observed. Make sure the bags are tightly sealed.
4. Have each student measure the mass of their bag and record that measurement in their lab notebook before taping the bag to the window or wall. Make sure the sample cup is right-side-up with the ice inside. If you wish, you can use any remaining class time to introduce the locations on Earth where water is stored (Step #10 of the Water Cycle discussion lesson plan below).
5. The following day, make some observations of the bags before taking them down. The ice should have melted and some condensation will have appeared on the sides of the bag and run down the sides of the bag to collect below the cup.
6. Take the bags down and remove any tape. Measure the mass of the bags and compare the measurement to the previous day.
7. Ask the students: Did anything surprise you?  Did everything happen according to your predictions? Flow directly into the Water Cycle discussion below.

Water Cycle discussion and storytelling:

1. Begin by setting the glass of ice water on the table at the front of the room. Ask the students to make observations of the glass. What is happening to the ice? What is happening on the outside of the glass? Why are these things happening?
2. Allow these initial observations to transition into a discussion of phase change. Ask students what they know about how and why water can transition from ice to liquid water to water vapor. Students may or may not know about how increasing temperature translates into molecular movement – that solids are solids because the molecules are locked in place and can only vibrate while in gases the molecules are energetic and move freely.
3. Invite 9 volunteers to come to the front of the room. Each student represents one molecule of water. Have them stand closely together in 3 rows of 3 students and interlock arms. They now represent water in its solid form – ice. Tell them that they are cold. They may shiver and vibrate a little but should remain bound together.
4. Now tell them you have placed the glass of water in a sunny window and the molecules of water in the ice cube have begun to get energized. They can now move around but should stay together in a cluster. They have melted and become liquid water. They should naturally unlink their arms and perhaps might join hands. Allow them to “flow” around the room and use that to illustrate the fluid motion of liquids. If you wish, you can introduce the idea of hydrogen bonding and surface tension as the reasons that liquids stay together.
5. Now tell them that the sun has become really warm and they are very very excited and can move about freely. The cluster of 9 will soon disperse about the room, probably colliding with desks, other students and the walls of the room. You may need to have the water molecules “freeze” temporarily in order for your explanation to be heard by the students. They have evaporated and now represent water as a gas – water vapor or steam.
6. Finally, tell them that the sun has set and it is beginning to become cold. When they collide with another water molecule, they should “stick together for warmth”. Soon all the water molecules will form a liquid again. They have now condensed back onto a liquid. You may take things all the way back to the beginning again and tell the molecules to freeze solid by linking arms once again.
7. Thank your water molecules and have them return to their seats. Review the process of phase change that they observed, noting the way that temperature changed the behavior of the molecules.
8. Ask the students where the energy that caused the temperature change came from. (The sun.)
9. Point out that this process – the phase changes of water powered by the sun – is what drives weather patterns, the movement of water around the globe, and the resulting erosion that shapes our landscape. Also point out that while water changes state and moves around, it is rarely created or destroyed. The water that exists on the planet today is OLD. At one time, the water molecules they drank this morning were once in the oceans when the Earth first formed and perhaps even were drunk by a dinosaur and later peed out again. If you did the mini-investigation, draw an analogy between the mini-investigation and the water cycle. The quantity of water in the bag stayed the same just like the quantity of water on the planet has stayed the same since the planet was formed. Just like in the bags, the water on the planet continually changes state and moves around from place to place.
10. Give students the handout and turn on the overhead projector with the water cycle drawing.
11. Invite students to name places on or around the planet where water can be found in any of its forms. As students provide one of the 6 major locations where water is stored (surface water, atmosphere, precipitation, glaciers, groundwater, living organisms) fill in that area on the water cycle transparency and have students copy our labels onto their own diagrams. Discuss the importance of each of the storage areas as you label it (see Teacher Background).
12. Next, ask students how they think water moves from place to place. As they point out each part of the water cycle (evaporate, condense, melt, freeze, percolate, transpire, drink, excrete) introduce an arrow and a label for the diagram.
13. Once the diagrams are completed, read or tell the students a story of a water molecule that makes a journey through the water cycle. An example of a story that follows a drop of water may be found on the USGS site. There is also a Magic School Bus episode by Pat Relf where Ms. Frizzle’s famous class takes a journey through the water cycle.
14. Tell the students that they now have the job of telling the story of a water molecule that makes its own journey through the water cycle. Notice that each of the locations where water is stored has a number. Students will roll a dice to figure out where each water molecule will begin and end its journey. On its way, the water molecule must travel through at least 4 different locations including a living organism.
15. Allow students time to outline their stories during class and check that each student has a reasonable story outline. The story itself can be completed as homework.