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The Arizona STEM Acceleration Project

Saltwater vs Freshwater

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Saltwater vs. Freshwater

A 5th Grade STEM Lesson

Lisa Nielsen

July 2023

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Notes for Teachers

Students should work in small groups of 2-3.
Best to break apart this lesson over a few days to see maximum results.
Allow students to take risks and experiment. It is okay if their design is not successful. The reflection and understanding the function is the most important.
Use models to show saltwater changing to freshwater through the movement of particles. Gather information to aid in building a successful model.
Check the speaker notes in this lesson for more information, details, and links.

List of Materials

Salt
Water
1 lite bottles (5-6)
Small measuring cups (3 per team)
ACS Freshwater visual experiment Cards
Research samples
Recyclables (clear plastic bottles, cups, plastic wrap, rubber bands, straws, tape)
Heat source or outdoor area in full sun
Evaluation sheet

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Standards

Science

5-ESS2-2. Describe and graph the amounts of saltwater and freshwater in various reservoirs to provide evidence about the water distribution on Earth.

5.P1U1.1 Analyze and interpret data to explain that matter of any type can be subdivided into particles too small to see and, in a closed system, if properties change or chemical reactions occur, the amount of matter stays the same.

Math

5.MD.B Represent and interpret data.

Percentages

Engineering

Science and Engineering Practices

● ask questions and define problems

● develop and use models

● plan and carry out investigations

● analyze and interpret data

● use mathematics and computational thinking

● construct explanations and design solutions

● engage in argument from evidence

● obtain, evaluate, and communicate information

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National Standards

Next Generation Science Standards (NGSS)

5-ESS2-2: Describe and graph the amounts of salt water and fresh water in various reservoirs to provide evidence about the distribution of water on Earth.

Connection: Students engage with the concepts of saltwater versus freshwater distribution and potentially graph the amounts collected or existing in reservoirs as part of the lesson's context.

5-PS1-1: Develop a model to describe that matter is made of particles too small to be seen.

Connection: Students use models to demonstrate how saltwater changes to freshwater through the movement of particles (evaporation and condensation) during the desalination process.

3-5-ETS1-1: Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost.

Connection: Students are challenged to design a device using specific materials (bottles, cups, plastic wrap) to separate freshwater from a saltwater mixture, addressing the need for drinkable water.

Common Core Mathematics (CCSS.MATH)

5.MD.B.2: Make a line plot to display a data set of measurements in fractions of a unit (1/2, 1/4, 1/8).

Connection: The lesson involves "Represent and interpret data," likely requiring students to measure the volume of freshwater collected in their small measuring cups and graph the class results.

MP4: Model with mathematics.

Connection: Students apply mathematical concepts to calculate percentages or efficiency of their desalination devices, interpreting the data gathered from their prototypes.

Common Core English Language Arts (CCSS.ELA)

W.5.2: Write informative/explanatory texts to examine a topic and convey ideas and information clearly.

Connection: The assessment requires students to answer reflection questions such as "How was the freshwater able to separate from the saltwater?" and explain the need for desalination, requiring written technical explanations.

SL.5.1: Engage effectively in a range of collaborative discussions (one-on-one, in groups, and teacher-led) with diverse partners on grade 5 topics and texts.

Connection: Students work in small groups of 2-3 to brainstorm, build, and test their designs, necessitating collaborative communication.

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Objective(s):

I can describe the amounts of saltwater and freshwater found on Earth.

I can create a visual representation of all the water on earth using graphs, data and visuals.

I can construct an explanation for the process of changing saltwater to freshwater.

I can design and build a device that changes saltwater to freshwater.

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Agenda (5 Days)

What is the amount of freshwater on Earth?
Represent and Interpret freshwater data
Design and create a device that can change saltwater into freshwater
Test design
Evaluate design and peer feedback

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Phenomenon: If you put all the freshwater on Earth into the ocean, it would still be salty.

Engage students with a quick taste test challenge. Allow them to taste salty water.

Provide each student with a separate Q-tip and have them dip it in a 1 liter jar of saltwater - about 5% (one part salt 19 parts water) and then add 25 ml of freshwater to the jar and have them use a new, unused Q-tip to taste the saltwater. This simulation models the small amount of freshwater that goes into the ocean each year and the small amount of Ocean water that evaporates. Use as part of introducing the Phenomenon to students. The water cycle is changing ocean water into saltwater all the time. Students can develop questions in pair share and while engaged in the class discussion.

Allow the students to fill the cup the rest of the way with freshwater. Have them taste again! Can you still taste the salt!

Can we drink saltwater? Why not?

Any fresh water that enters the ocean will become salty.

Why does this matter?

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Why do we describe water as a limited resource when we have enormous oceans of water?

Demonstration

Let’s distribute the world’s water

Intro/Anticipatory Set/Opening

Using this short activity from the ACS (American Chemistry Society) Students will experiment with the amount of freshwater on Earth.

This is a great way for students to represent the data visually and utilize measurement and mathematics to deepen their understanding of the problem.

In this demonstration - You will need a 1 liter bottle and 3 small clear measuring cups.

This bottle of water is a model that represents all the water in our world. In our model, all of the water on our planet is represented by just 1-liter of water. • How many milliliters are in one liter? 1000 mL. • What percentage of this water do you think represents all of Earth’s saltwater? [Have participants guess quickly as it is unlikely that anyone knows the answer.] • What percentage of this water do you think represents all of Earth’s fresh water? [Point out that guesses for saltwater and freshwater should add up to 100 because percent means “out of 100.”]

This activity is recommended to perform as a table group (4 members). If short on supplies the teacher could demonstrate this.

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Identify the problem

Research - Jigsaw articles

How the Earth Makes Fresh Water

Solar Water Plant

What is a Drought?

What is the problem?

What if….?

Can we change saltwater into freshwater?

Class Discussion -

Q: How does the scale of saltwater compare to the scale of freshwater?

Q: How does saltwater become freshwater on Earth?

Q: Why does saltwater taste different than freshwater even though they look the same?

Q: Why is freshwater essential for living organisms?

Q: Why do we describe water as a limited resource when we have enormous oceans of water?

Students are ready to begin defining the problem. Allow students to generate possible problems they have discovered after their initial investigation into fresh water.

*Research

*. Obtain information about how salt water becomes fresh water naturally on Earth (water cycle).

* Read the article about how humans utilize this process in the middle east to create freshwater in the desert!

* Learn about climate change and drought.

*Jigsaw*

You can use the jigsaw method to speed up your research process. Instead of having each student read several articles, here’s what you could do.

Jigsaw is a cooperative learning strategy that enables each student of a “home” group to specialize in one aspect of a topic (for example, one group studies habitats of rainforest animals, another group studies predators of rainforest animals). Students meet with members from other groups who are assigned the same aspect, and after mastering the material, return to the “home” group and teach the material to their group members. With this strategy, each student in the “home” group serves as a piece of the topic’s puzzle and when they work together as a whole, they create the complete jigsaw puzzle.

After the research, we want students to brainstorm possible solutions to the water crisis.

**We have a limited amount of freshwater. There is an unlimited supply of water in our oceans, only we can’t drink it! If we could find a way to remove the salt from that water, then we could utilize it.

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Solution

Design and build a device that changes saltwater to freshwater.

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Design and build a device that changes saltwater to freshwater

Criteria

Separates the saltwater mixture from the freshwater mixture
Collects water efficiently without escaping into the air
Can stand upright on its own

Constraints

All devices will use the distillation process (evaporation and condensation) to produce the freshwater.

Uses teacher-provided materials: Clear plastic bottles, cups, containers, sponge,, plastic wrap, rubber bands, tape, straws, weights

Hands-On Activity:

***It is recommended that students clearly define the criteria and constraints associated with this task.

Criteria - What will the design need to do in order to be considered successful?

Students will understand that the freshwater will evaporate to the top of their device. Many times, students will not consider what will happen to it when it comes back down. How can we collect this freshwater so that it does not end up in the saltwater again.

Constraints (limitations)

We will be limiting our students to devices that use the distillation process to capture the freshwater. They should be working on ways to capture the condensation and not designing a filter for this particular investigation. If students are interested in filters, you may provide that as an extension.
Materials - Clear plastic bottles, cups, containers, sponge,, plastic wrap, rubber bands, tape, straws, weights
If you have access to other materials not listed, feel free to add to your list

*Engineering tip - If you have a limited supply of items, consider adding a cost to each item based on their popularity or effectiveness. Challenge students to create a design that is the most cost effective.

Use the engineering process. Students should always draw and label a diagram of their design. Note: A version of the engineering a design process has been provided off slide.

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Test Design!

Place your device in full sun for a period of 24 to 48 hours.

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Assessment

Criteria

Rate Yourself

Separates the saltwater mixture from the freshwater mixture?

1 2 3 4

Collects water efficiently without escaping into the air?

1 2 3 4

Can stand on its own?

1 2 3 4

Effort and creativity

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What went well in your design?

If you had to do this challenge again, what would you do differently?

How was the freshwater able to separate from the saltwater?

Why there is a need to change salt water into fresh water

Evaluation Form

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Differentiation

Use research videos for developing readers.
Create a prototype that students can use to inspire their own design.
Provide a design with build instructions.

Remediation

Extension/Enrichment

Students can experiment with creating a filter that can remove the salt from water.
Connect water device to drought crisis in Southern California. Students investigate the changing climate and what might be causing the drought. Students research and present how engineers are solving the problem.
Students can create art with saltwater using the same process using black paper and over salinated water. Dip a Qtip into the mixture and draw a design. Allow the drawing to dry and watch as the salt is left behind to reveal the image.

This slide should be hidden or not shared with students.

Remediation-

This lesson involves a fair amount of research. For students that may have difficulty reading, here is a video resource you can use in place of an article

To help students think through the process and get unstuck, have some prototype ideas already created for students to use as a reference.
Here is a prototype design build with instructions if needed. EXAMPLE

Extensions -

During the lesson, some students may have shown interested in creating a filter than can take the salt out of the water. If time allows, you can have students explore this ideas. some materials to try are coffee filters, sand, gravel, carbon, and cotton.
California and the southern United States is facing one of the worst droughts on record. Students could research further into the drought crisis in California and beyond. Students can research how current engineers are addressing the problem and what issues exist with water desalination projects.
Another aspect of this lesson is that matter is made of particles too small to be seen with the human eye. We can demonstrate this with an art project. If students dissolve enough salt in water they will reach a point where it will no longer incorporate. When this happens students can create an art project to demonstrate what happens when the water evaporates. Students get a black piece of construction paper. With the salt water mixture, use a qtip to draw or create an image. let the image dry. The water will evaporate, leaving behind the salt. The image drawn will reveal itself as it dries. This is a very nice way to connect back to the chemistry and matter in the process.