Summary

In this lesson, students will learn about the phase changes of matter by focusing on water. During the course of two days students will perform several short experiments in order to change the state of water and they will record their observations.

Grade Level

Elementary school

Objectives

By the end of this lesson, students should be able to:

• Recognize the three main states of matter: solid, liquid and gas.
• Understand that the change in the state of matter is a physical change and is not due to a chemical reaction.
• Explain the phase change associated with each of the following vocabulary terms: freezing, melting, evaporation, condensation.

Chemistry Topics

• States of Matter
• Phase Change
• Physical Changes

Time

Teacher Preparation: 30 minutes

Lesson: 2 days (Day 1- 1.5hrs; Day 2 – 1hr)

Materials

• Bag of ice (enough for each student to have 1-2 cubes)
• Clear Plastic cups (one per student)
• Clear sealable sandwich bag (one per student)
• Permanent marker pens (one per student)
• Paper towels
• Access to a window that gets some sunshine
• KWL chart (Know/Want to Know/Learn)

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

• I suggest that on the first day that you begin this activity, start it in the morning. Instructions for each day are found below.
• Having a parent help with the first day is advised.
• As an extension for older students, you could discuss the water cycle in greater detail using this NASA resource: Earth's Water Cycle. Students can investigate the water molecule and the hydrogen and oxygen atoms that compose it. Students can draw and label the parts of a water molecule
• Vocabulary used throughout activity:
  • Atoms –the smallest particles, the building blocks of matter.
  • Physical Properties –observations or descriptions about a substance. Often these are measureable by direct observation. Examples include: Phase changes, mass, color, volume, density.
  • Phase Change – the shift from one form of matter to another, for example, the change of liquid water to ice. This is a physical change, not a chemical change.
  • Freezing - when matter changes phases from a liquid to a solid.
  • Melting - when matter changes phases from a solid to a liquid.
  • Evaporation - when matter changes phases from a liquid to a gas.
  • Condensation – when matter changes phases from a vapor (gas) to a liquid.

Day 1 – 1.5 hour

• Opening: Play song, Sesame Street: The Water Song
• Tell students that they are going to be chemists today and investigate the physical properties of water and the phase changes of water.
• Share applicable information about water from the following resources:
  • Water Facts for Kids
  • Ask students to share with a partner what they know about water. The class will participate in a brief discussion of their ideas. The teacher will write ideas on the “Know” portion of the class KWL chart (example below):
    

• Next, ask students what they want to learn about water and its phase changes. The class will participate in a brief discussion of their ideas. The teacher will write ideas on the “Want to Learn” portion of the KWL chart.
• Students will begin the first experiment involving ice under the teacher’s direction.
  • Materials needed for this portion include:
    • 1-2 ice cubes for each cup
    • Clear Plastic cups (one per student)
  • Give students 1-2 ice cubes in a clear plastic cup.
  • Students will observe, discuss, share, and record the physical properties of the ice 3 times (at the start of the experiment, after 20 minutes and again after 40 minutes) on their student data sheet.
  • At the end of the third observation guide a discussion about how the physical properties changed over time. The solid ice melted into liquid water because the temperature in the room is warmer than the freezer where the ice cubes came from. As a result the water melted and changed forms, but the substance itself is still water. This is called a physical change, and it is reversible.
  • Identify this physical change as “melting” and the reverse physical change as “freezing.”
  • Students should not discard the water in their cups, as they will use it for the next portion of the experiment.
• Students will begin the second experiment involving water under the teacher’s direction.
  • Materials needed for this portion include:
    • Water from the cup in the previous experiment
    • Sealable plastic sandwich bag
    • Permanent Marker

1. Pass out a quart sized sealed bag and permanent marker to each student. Students will write their names on the bag.
2. Tell students to pour their water from the cups into their bag. Students should record their observations of water on their student data sheet.
3. The teacher should guide the discussion to include the physical properties of liquid: it takes the shape of the container, it is wet, odorless, clear (transparent), and you are unable to hold it between your fingers. You could also measure the mass, volume and/or temperature.
4. Students will seal the bags securely and tape them to a sunny window to observe what happens to the liquid water when the sun heats the water in the sealed bags.
5. Students should make a prediction explaining what they think will happen to the water when it is heated by the sun. This should be recorded on their student data sheet in the Analysis section.
6. Leave the bags on the windows until the following day.
7. Clean-up!

Day 2 – 1 hour

• Students should find their bag on the window and record their observations on their Student Data Sheet.
  • A layer of tiny water droplets attached to the inside of the plastic bag should be seen above the liquid water.
• Explain that the water in the bag was heated by the sun and changed from a liquid into a gas (vaporization or evaporation). Evaporation is the process in which the molecules of a liquid break away from the surface of the liquid and become a gas (water vapor).
• Discuss the physical properties a gas. The teacher should guide the discussion to include the physical properties water vapor: it takes the shape of its container; the molecules are spread out, and fill the container. Volume and temperature can be measured.
• Discuss the reverse process of evaporation, called “condensation”. Condensation is the process in which molecules of water vapor come together to form liquid water. The little water droplets on the side of the bag are an indicator that condensation occurred.
• Instruct students to clean up.
• Have the students watch and listen to The Water Cycle Song by Have Fun Teaching to connect this experience to the rea-world.
• Show Changing States of Matter to students.
• The teacher will review with students what they should have learned from the experiment and discussions on water and then complete the learning outcomes on the “Learned” portion of the KWL chart.

Connect to Reading

Using TheWaterPage.com teach the kids about the importance of our natural resource, water. Pose the problem that the custodians noticed students leaving the faucets running in the sinks and the drinking fountain buttons pushed down. Also, our custodian heard from other custodians that “Yikes!, some students are even wasting water at their homes!”. The custodian asked for our help to let other students in the building know we have a real problem with wasting water in school and at home. They asked if we could let students know ways they can conserve water. Guide students into suggesting we make posters using tips from TheWaterPage.com.

Invite a local hydrologist into the classroom and explain his/her job. The hydrologist should explain how his/her job helps our community, has changed the local community over time, and has helped identify a problem and solution in the past. If a hydrologist is unavailable visit The US Geological Survey website with your students to learn all about the field of hydrology.