Day 1: Water Properties
In preparation for the lesson, leave the stalk of celery at room temperature for several hours so that it begins to wither; this will speed up the capillary action demonstration. Prepare the materials for the oil and water activity for each group: beaker, food coloring, vegetable oil, dropper, spoon, and access to water.
Begin the lesson with a demonstration of capillary action. Fill a beaker or tall glass about two-thirds full of water and add 5–10 drops of food coloring. With a sharp knife, carefully cut about an inch (2 cm) off the bottom of the stalk of celery. Cut it at a slight angle and try not to “crush” the tubes. Keep the leaves attached to the top. On the Celery Experiment worksheet, have students write a prediction about what will happen, and draw the celery before you place it in the water (S-8-8-1_Celery Experiment and KEY.doc
).
After discussing the common uses of water, have students view the two-minute video from the following Web site: http://videos.howstuffworks.com/howstuffworks/458-how-water-works-video.htm. After the video, have students discuss the various properties of water that were mentioned. If Internet access is not available, a transcript is provided as a resource (S-8-8-1_How Water Works Transcript.doc).
After viewing the video on the properties of water say to students, “Now that we have watched a short video clip to give us information on water, let’s look more specifically at the properties of water.” Hand out a copy of Water Properties to each student (S-8-8-1_Water Properties and KEY.doc). Have students read through the information and answer the questions independently. Review the correct answers once students finish.
Have students work in groups of three or four. Give each group the Oil and Water worksheet, as well as a beaker, food coloring, vegetable oil, dropper, spoon, and access to water (S-8-8-1_Oil and Water and KEY.doc). Define density, and then have each group follow the procedure on the worksheet and answer the questions. Conduct a follow-up discussion on the density of water compared to the density of oil. Close the lesson by discussing the following question: “Imagine you work in a chemistry lab. You find a container of colorless liquid. How can you test it to find out if it is water or a different substance?”
Day 2: Saltwater and Freshwater Systems
In preparation for the lesson, gather materials for the “All the Water in the World” demonstration, and fill the five-gallon aquarium with water.
Say to students, “So far, we have discussed the properties of water. We are going to move forward by comparing freshwater and saltwater systems. Learning about these different types of systems also helps us learn more about the properties of water. Take out your science journals and write down how you believe freshwater can become saltwater in nature. You have five minutes to brainstorm.”
As students are working, walk around the classroom to assess their thinking. After students have finished recording their responses, ask them to share their theories. As students share their theories, write their responses on the board. Explain that saltwater is made during the movement of water on land over time. The components of rock are eroded and become part of a “salty” solution.
Take a moment to tie in what students are learning to what they may have seen in movies or television shows. Say to students, “We have watched movies where someone is stranded in the middle of the ocean. Why do you think you shouldn’t drink saltwater if you are ever stranded in the middle of the ocean?” Give students time to brainstorm. Share with students that saltwater is not suited to be used as drinking water, because salt drains water from human bodies. Anytime people drink saltwater, they risk dehydration.
Show students a globe. Say to students, “We can see, by looking at this globe, that most of the Earth is covered in water. What percentage of the Earth do you think is covered in freshwater? What percentage do you believe is covered in saltwater?” Allow for time for student responses. After taking their responses, inform students that about 71% of the earth is covered with saltwater. About 1% of the earth is covered in freshwater. Tell them that if all of the water in the world was poured onto the United States, it would cover the land to a depth of 90 miles (145 kilometers).
Use a projector to show students the graph and pie charts in the Where Is Earth’s Water Located? handout (S-8-8-1_Where Is Earth’s Water Located.doc):
Source: http://ga.water.usgs.gov/edu/earthwherewater.html
Have students interpret the data shown to explain the distribution of Earth’s water and the availability of freshwater to humans.
Before beginning the next presentation, hand out a copy of New Vocabulary to each student (S-8-8-1_New Vocabulary and KEY.doc). Inform students that this vocabulary is important to the presentation they are about to give.
Write the following terms on the board: ice caps, glaciers, and ground water. Say to students, “Give me some ideas of what you believe the definitions are for each of these words.” Take responses from students. After getting responses, write the definitions on the board. Allow students time to copy the definitions and create an illustrated picture on the worksheet.
Next, allow a student to participate in the following visual demonstration, “All the Water in the World”:
- Present to the class the five-gallon aquarium filled with water.
- Using a measuring cup, remove 18 ounces of water from the aquarium.
- Color the remaining water in the aquarium green with food coloring. Say to students, “This water remaining in the aquarium represents the amount of water that is in our oceans. The 18 ounces is proportionate to water that is not ocean water.”
- Pour 15 ounces of the 18 ounces into an ice cube tray. Say to students, “This represents that amount of water that is held in glaciers and icecaps. This water is not readily available for our use. Give me some ideas of why you think this water would not be readily available for our use.” Students answers should vary, but they should mention that the water in glaciers and icecaps is frozen, so it cannot be used right away.
- Explain to the class the 15 ounces of water in the ice cube tray is equal to the amount of water in your ice pack. Float the ice pack in the aquarium to represent the total amount of water held in glaciers and icecaps.
- Say to students, “The remaining 3 ounces represents the world’s available fresh water. Of this amount, only one dropper full is held in the world’s fresh water lakes and rivers.”
- Explain to students that the remaining water (approximately 2.5 ounces) is ground water. Pour this remaining water into a cup of sand and gravel. Explain that ground water is held in soil and fractures of rock.
- At the end of this presentation ask students to write down two thoughts or questions that they have after learning about water availability. Allow for time for students to ask questions and share their thoughts.
Project the Water on Earth data table (S-8-8-1_Water on Earth.doc). Define potable as suitable for drinking, and have students interpret the data table to identify sources of potable water on Earth. Ask students questions to guide them in relating the data table to the demonstration, such as “How did we represent freshwater lakes and rivers in the demonstration? What percentage of the world’s water is found in rivers?”
Day 3: Saltwater and Freshwater Experiments
Before the lesson begins, gather materials for each experiment, and divide them for lab groups. Inform students they will conduct two different experiments to help them learn more about the properties of saltwater and freshwater systems. The first experiment focuses on the density of saltwater and freshwater systems. The second experiment focuses on determining whether saltwater or freshwater conduct electricity.
Say to students, “You will be completing an experiment to show how the density of water can be changed by dissolving salt in it.”
- Divide the class into groups of three or four.
- Each group should have an egg, beaker filled ¾ of fresh water, salt, and a tablespoon. Each group should also have an Egg: Sink or Swim? worksheet (S-8-8-1_Egg Sink or Swim and KEY.doc). Advise students to answer the questions as they work.
- Have students use a spoon to gently place a fresh egg in the beaker of fresh water. Have students record what they observe happening to the egg in the beaker of freshwater.
- After recording their observations, have students take the egg out the beaker.
- Students stir one tablespoon of salt into the beaker of water until it dissolves completely.
- Have students place the egg back in the beaker of water.
- Have students record what they observe happening to the egg this time.
- Have students repeat the last two steps, each time adding another tablespoon of salt to the water.
- Once each group’s egg has reached the top of the beaker, have students record how many tablespoons it took to get the egg to reach the top of the beaker. (Students need about 10–11 tablespoons to get the egg to reach the top.)
Have each group discuss why the egg floated in the saltwater, but not in the freshwater. Use this as an opportunity to engage students in a class discussion. Have students recall their different experiences swimming in freshwater and saltwater if they have had this experience. Say to students, “You will now complete a second experiment to determine whether saltwater or freshwater conducts electricity.”
Have students work in the same small groups of three or four students from the previous experiment. Give each group a copy of the Does Saltwater or Freshwater Conduct Electricity? handout (S-8-8-1_Electricity.docx).
- Each group needs masking tape, a 9-volt battery, a buzzer, two craft sticks, one tablespoon, aluminum foil, and a beaker of water.
- Have students cover both craft sticks with aluminum foil.
- Next students take their buzzers and tape the red wire to the positive end of the battery (+ sign).
- Students tape one foil covered craft stick to the black wire, and tape the other one to the negative side of the battery (− sign).
- Have students bring the two sticks together. The buzzer should sound. If the buzzer doesn’t sound, advise students to double check that everything is taped together properly.
- Students fill the beaker halfway with water.
- One student from the group scoops three tablespoons of salt into the beaker of water. Another student stirs the salt into the water until it dissolves.
- Next, a different student puts the tips of the metal sticks in the salt water about an inch apart. Inform students to be sure the two sticks don’t touch each other. As the two sticks are in the saltwater, the salt acts as a conductor connecting the metal sticks. This completes the circuit and results in the buzzer sounding.
- Once students finish, have them repeat the experiment with the freshwater. Ask students to determine why the buzzer sounded in the saltwater, but not the freshwater.
As a closing activity, draw a Venn diagram on the board. Say to students, “We have created a good list of similarities and differences between freshwater and saltwater systems. Each of you will copy this Venn diagram into your science notebooks. Be sure to record all the information because this Venn diagram can be used as a study aide for a later date.” Use this diagram to compare freshwater and saltwater systems.
Say to students, “After completing these two experiments, describe some similarities and differences between freshwater and saltwater.” Student answers will vary, but students should record that salt water is denser, conducts electricity because of its ionic content, and chemically has more ingredients. Saltwater covers more of the Earth than freshwater. Saltwater has a lower freezing point than freshwater. Humans can drink freshwater, but not saltwater. Freshwater has a higher boiling point. Freshwater and saltwater are both found on Earth.
Extension:
- Students who need an opportunity for additional learning can complete a graphic organizer on the properties of water, using the Water Properties Graphic Organizer (S-8-8-1_Water Properties Graphic Organizer.doc).
- Students can also make flashcards. The flashcards can focus on the properties of water. One side of the flashcard should have the information and the other side should have a pictorial representation.
- Students who may be going beyond the standards can learn how much of the Earth’s water is readily available for use. Ask students to create an organization with the focus of conserving water. Students give their organization a name, a mission statement, a mascot, and construct a plan describing why water conservation is important and how their organization intends on conserving water. Students prepare their material as a poster presentation. After completing the assignment, they should present their posters to the class.
- Have students read about how Pennsylvanians get their groundwater and how much groundwater people in their county use each day. This information can be found on pages 6–8 of the “Geology of Pennsylvania’s Groundwater” available at www.dcnr.state.pa.us/topogeo/education/es3.pdf. Have students write a one-paragraph summary of groundwater use in Pennsylvania.