Hands-on Activity Exploring Density Solutions Using the Engineering Design Process

Learning Objectives

After this activity, students should be able to:

• Design and create mixtures using the engineering design process.
• Test the relative density of mixtures.
• Evaluate whether a mixture is a solution.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

State Standards

Materials List

Each student needs:

• Exploring Density Solutions Worksheet

Each group needs:

• 1 box of food coloring with at least three different colors
• 1 set of measuring spoons
• 1 set of measuring cups
• stirring rods (or spoons)
• 3 glass beakers (500 mL)
• wooden, metal, and plastic blocks of various densities
• rulers

For the entire class to share:

• water
• milk
• salt
• sand
• cocoa powder
• baking soda
• cornstarch
• flour
• sugar
• vinegar
• lemon juice
• vegetable oil
• digital mass scale

Worksheets and Attachments

Pre-Req Knowledge

Students should:

• Know the three basic states of matter.
• Be able to differentiate between what constitutes a mixture and a solution.
• Be familiar with density and relative density.

Introduction/Motivation

Have you ever wondered why some things float in water, while others sink? Engineers often ask questions like this when they design things such as boats, submarines, or even new kinds of materials.

In this activity, you'll become chemical engineers and explore what makes objects sink or float by experimenting with different materials. You'll also learn about important ideas such as density, mass, and weight, which help us understand why some things are heavier or lighter, even if they're the same size. By the end, you'll be able to create your own mixtures with different densities using the engineering design process, just like chemical engineers do when they design new products or processes! Let’s dive into the world of engineering and discover how science helps us solve real-world problems!

Procedure

Background

The main difference between a mixture and a solution lies in how the substances are combined, and their properties:

1. Mixture: A mixture is a combination of two or more substances that are physically combined but not chemically bonded. The individual components retain their own properties and can usually be separated by physical means, such as filtering or sorting. Mixtures can be homogeneous (uniform throughout) or heterogeneous (not uniform; the different substances can be seen).
2. Solution: A solution is a specific type of mixture where one substance (the solute) is completely dissolved in another substance (the solvent), creating a homogeneous mixture. In a solution, the solute particles are distributed at the molecular level, so it looks uniform and cannot be separated by physical means such as filtering. An example of a solution is salt water, where salt is dissolved in water.

In summary, although all solutions are mixtures, not all mixtures are solutions. Solutions are uniform and consist of dissolved substances, whereas mixtures can be either uniform or non-uniform and consist of substances that can often be separated.

Before the Activity

• Collect the materials for the activity and have them ready for student use.
• Make copies of the Exploring Density Solutions Worksheet. (one per student)
• Prepare to project the Density Solutions Engineering PowerPoint in presentation mode, starting on Slide 3, “What is Engineering?”

With the Students

Day 1

Introduction: (15 min)

1. Project the Density Solutions Engineering PowerPoint for the class to see.
2. Read the title of Slide 3: “What is Engineering?”
3. Have one student volunteer to read the response to the prompt.
4. Lead the class to brainstorm specific things that engineers might design and create that are not on that list. (Potential answers: bridges, cars, airplanes, roller coasters, computers, phones, robots, medical devices, solar panels, wind turbines, packaging for food, water filters, video games, etc.) Encourage students to be open-minded and think outside of the box.
5. Jot the student responses on chart paper or a dry erase board under the heading “What do engineers design?”
6. Show Slide 4 and read its title, “What is an Engineer?” Have a volunteer read the description of what an engineer is.
7. Show Slide 5 and read its title, “How Does Engineering Happen?” As a class, read and discuss the engineering design process diagram on Slide 5.
8. Show the class the video “Crash Course: The Engineering Process” (5:16 minutes).

Ask: (20 min)

1. Give each student an Exploring Density Solutions Worksheet.
2. Tell students that they will be designing specialized mixtures with different densities for this activity.
3. Ask the class: “What makes objects sink or float?”
4. Let students share their thoughts.
5. Remind the class that engineers find out how things work, and that today they are going to become engineers and explore what makes objects sink or float in water.
6. Split the class into groups of 2-3 students.
7. Give each group a 500 mL beaker.
8. Have each group fill their beaker with water up to the 300 mL mark.
9. Pass out the density blocks.
10. Give groups 10 minutes to use the density blocks to explore what makes those different blocks sink or float.
11. Let students use their rulers and the mass scale to find the blocks’ mass and weight.
12. Have students record their observations and reflections in complete sentences in the “Ask” section of the Exploring Density Solutions Worksheet.

Research: (15 min)

1. Pose this question to students: “What is the difference between mass, weight, and density?”
2. Have students use their school’s online research resources and/or their science textbooks to find out what mass, weight, and density are, and how they are different.
3. Have students record their findings in their “Research” section of their Exploring Density Solutions Worksheet.
4. Bring the class back together to discuss the students’ findings as a class.
5. Discuss the following concepts:
1. Density (Answer: Density is the amount of mass [or matter] packed into a specific space or volume. It helps explain why some objects are heavier than others, even if they're the same size. If an object has a high density, it has a lot of mass in a small space, while a low-density object has less mass in the same amount of space. Density is often used to determine whether something will float or sink in water.)
2. Relative density (Answer: Relative density is a way to compare the density of one substance to the density of another, usually water. It helps us understand whether something will float or sink. If an object has a relative density less than 1, it will float in water because it’s less dense than water. If its relative density is more than 1, it will sink because it’s denser than water. Relative density helps us compare how heavy or light something is compared to water or another material.)
3. Weight (Answer: Weight is the force that gravity exerts on an object, which depends on both the object's mass and the strength of the gravitational pull acting on it. It tells us how heavy something is. Weight is typically measured in units such as pounds or kilograms. For example, if you weigh yourself on Earth, your weight is the result of Earth's gravity pulling down on your mass. If you were on the moon, you would weigh less because the moon's gravity is weaker than Earth's, even though your mass would stay the same.)
4. Mass (Answer: Mass is the amount of matter or "stuff" that makes up an object. It tells us how much material is in something, no matter where it is. Unlike weight, which can change depending on gravity (such as on the moon), mass stays the same everywhere. Mass is measured in units such as grams or kilograms, and it's what makes things heavy or light. The more mass something has, the heavier it feels.)
6. Make sure all students have a clear understanding of these terms, and make sure they can differentiate between density, mass, and weight.

Day 2

Imagine: (20 minutes)

1. Have students pull out their Exploring Density Solutions Worksheet.
2. Tell students that, based on their previous research, they are now going to imagine/brainstorm how they can create different solutions, each with a different density.
3. Ask the students: “How would you design and test these solutions?” Encourage students to think outside of the box, and to not be afraid of coming up with ideas that might not work.
4. Have students individually come up with 5-6 brainstormed ideas.
5. Have students write their individual ideas in the “Imagine” section of their Exploring Density Solutions Worksheet.

Plan: (30 minutes)

1. Tell students that in their groups they are going to design for three different mixtures. Tell them the following criteria:

1. Each mixture must be a solution.
2. Each mixture must contain three ingredients.
3. Each mixture must be 300 mL.
4. Each mixture must have a different density.

2. Highlight the idea of constraints. Make sure students know that the constraints of their activity are the materials they have available to work with. Tell them that engineers must operate within the constraints of the materials, budget, and time.
3. Have students share their brainstormed ideas with their group.
4. Have each group choose three ideas (or a mixture of ideas) to design.
5. Tell students to add a different color of food coloring to each mixture, to help keep track of which mixture is which.
6. Have students record their groups’ planned mixtures in their Exploring Density Solutions Worksheet, making sure to write a materials list and a procedure for each of the three mixtures they will design.
7. Have students brainstorm as a team how they plan to test the relative densities of their mixtures. (If any group gets stumped on this, remind them about their initial “Ask” exploration of density.) (Note: This is another student-driven process, in which your main function is to manage behavior and respond to student inquiries.)
8. Have students write down how they will test the relative densities of their mixtures in the “Test” section of their Exploring Density Solutions Worksheet.

Day 3

Create: (15 minutes)

1. Give students 15 minutes to use their planned materials and procedures to create their mixtures. (This should be a student-driven process, with you providing guidance as needed.)

• Make sure students know that each mixture will go into a separate beaker.
• Remind students to use the correct color for each mixture.

2. When their mixtures have all been created, have students make observations and record them in their worksheets.
3. Have students note whether each mixture became a solution.

1. Give students 15 minutes to test their mixtures and write down their observations.
2. Make sure students write down their observations of each of their tests in the “Test” section of their Exploring Density Solutions Worksheet.

Improve: (10 minutes)

1. Tell students that now they are going to do what real engineers do, and use the results of their hands-on experiments to make an improvement on what they made.
2. Ask the students: “Did each mixture have a different density? How could you tell? If not, what can you change next time?” Have them discuss and record their responses in their Exploring Density Solutions Worksheet.
3. Ask the students: “Was each mixture a solution? How could you tell? If not, what can you change next time?” Have them discuss and record their responses in their Exploring Density Solutions Worksheet.
4. Have students record their reflections about this activity in their Exploring Density Solutions Worksheet.

Activity Exit Ticket (10 minutes)

1. Have students complete the Making Sense Assessment.

Vocabulary/Definitions

beaker: A glass container with a flat bottom used to hold and measure liquids.

density: A physical property that measures how closely packed together a substance's particles are.

mixture: A combination of two or more substances.

relative density: How the density of one material compares to the density of another material.

solute: The substance in a solution that is dissolved by another substance.

solution: A special type of mixture in which one substance (solute) is dissolved evenly into another substance (solvent).

solvent: The substance in a solution that dissolves another substance.

volume: The amount of space something takes up.

Assessment

Pre-Activity Assessment

The pre-assessment comprises student responses in the “Ask” section of their Exploring Density Solutions Worksheet. This pre-assessment gauges their existing understanding of density, mixtures, and solutions.

Activity Embedded (Formative) Assessment

The formative assessment comprises student responses in the “Research,” “Imagine,” and “Create” sections of their Exploring Density Solutions Worksheet. This will allow you to gauge each student’s level of participation and understanding.

Post-Activity (Summative) Assessment

The performance-based summative assessment comprises student responses in the “Test” and “Improve” sections of their Exploring Density Solutions Worksheet. These reflective responses will demonstrate their understanding of the physical properties of their mixtures, and require them to utilize the engineering design process.

Activity Exit Ticket: Have students complete the Making Sense Assessment.

Troubleshooting Tips

Because this is a student inquiry lesson in which students design mixtures and tests to evaluate relative density, not every group will use the exact same materials or procedures.

Remind students that in real life, engineers are constrained by the materials they have available. Likewise, as student engineers, they are constrained by the materials that their particular group has available.

Activity Scaling

Special needs students who require modifications to be able to participate in this activity can complete their Exploring Density Solutions Worksheet using drawings and photographs rather than words.

Student groups create the new and improved mixtures that they wrote about in the “Improve” section of their Exploring Density Solutions Worksheet. They test those improved mixtures to see if they actually fulfill the anticipated real-life applications.

Copyright

Contributors

Supporting Program

Acknowledgements

This curriculum was developed under National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement number DMR-1720595. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.