Diffusion of Water Molecules

20 teachers like this lesson
Print Lesson


SWBAT explain use the process of diffusion to demonstrate the presence of molecules in matter water.

Big Idea

In this lesson, students investigate how the temperature of water affects the time it takes for food coloring to mix with water (due to the movement of tiny molecules).

Lesson Overview

Inquiry Based Instructional Model

To intertwine scientific knowledge and practices and to empower students to learn through exploration, it is essential for scientific inquiry to be embedded in science education. While there are many types of inquiry-based models, one model that I've grown to appreciate and use is called the FERA Learning Cycle, developed by the National Science Resources Center (NSRC):

1. Focus

2. Explore

3. Reflect

4. Apply

A framework for implementation can be found here

I absolutely love how the Center for Inquiry Science at the Institute for Systems Biology explains that this is "not a locked-step method" but "rather a cyclical process," meaning that some lessons may start off at the focus phase while others may begin at the explore phase. 

Finally, an amazing article found at Edudemic.com, How Inquiry-Based Learning Works with STEM, very clearly outlines how inquiry based learning "paves the way for effective learning in science" and supports College and Career Readiness, particularly in the area of STEM career choices. 

Unit Explanation

In this unit, students will begin by exploring the properties of matter. Then, the class will investigate the mass of matter before and after physical and chemical changes by conducting investigations and constructing graphs. 

Summary of Lesson

Today, I open the lesson by demonstrating what happens when dish soap is added to a bowl of milk and food coloring. Students then explore how the temperature of water affects the movement of water molecules by investigating the process of diffusion. At the end of the lesson, students examine their investigation results and share their conclusions. 

Next Generation Science Standards  

This lesson will support the following NGSS Standard(s):

5-PS1-1. Develop a model to describe that matter is made of particles too small to be seen.  (lessons 3 & 4)

5-PS1-3. Make observations and measurements to identify materials based on their properties.  (lessons 1 & 2)

Scientific & Engineering Practices

For this lesson, students are engaged in Science & Engineering Practice: Science & Engineering Practice 6: Constructing Explanations and Designing Solutions 

Today, students construct explanations for the causes of phenomena. Their explanation includes: a claim that food coloring diffuses quicker in hot water than cold water. Then, they relate how this variable is related to the speed at which the water molecules are moving. Finally, the diffusion process helps students explain the presence of molecules in water that are too small to be seen.

Crosscutting Concepts

To relate ideas across disciplinary content, during this lesson I focus on the following Crosscutting Concept

Crosscutting Concept 1: Patterns 

Today, students discover the following pattern: food coloring diffuses slowly in cold water, a little bit faster in warm water, and fastest in hot water. Patterns such as these help strengthen student understanding. 

Disciplinary Core Ideas

In addition, this lesson also aligns with the following Disciplinary Core Ideas

PS1.A:  Structure and Properties of Matter

Matter of any type can be subdivided into particles that are too small to see, but even then the matter still exists and can be detected by other means. A model showing that gases are made from matter particles that are too small § to see and are moving freely around in space can explain many observations, including the inflation and shape of a balloon and the effects of air on larger particles or objects. (5-PS1-1)

Choosing Science Teams

With science, it is often difficult to find a balance between providing students with as many hands-on experiences as possible, having plenty of science materials, and offering students a collaborative setting to solve problems. Any time groups have four or more students, the opportunities for individual students to speak and take part in the exploration process decreases. With groups of two, I often struggle to find enough science materials to go around. So this year, I chose to place students in teams of two or three! Picking science teams is always easy as I already have students placed in desk groups based upon behavior, abilities, and communication skills. Each desk group has about six kids, so I simply divide this larger group in half or thirds. 

Gathering Supplies & Assigning Roles

To encourage a smooth running classroom, I ask students to decide who is a 1, 2, or 3 in their groups of three students (without talking). In no time, each student has a number in the air. I'll then ask the "threes" to get certain supplies, "ones" to grab their computers, and "twos" to hand out papers (or whatever is needed for the lesson). This management strategy has proven to be effective when cleaning up and returning supplies as well!  


20 minutes

Teacher Note: This lesson was inspired by yesterday's lesson, Investigating Water Molecules. While investigating how food coloring is "stirred" and spread throughout a beaker of water (due to the movement of water molecules), some students commented, "I wonder if the food coloring mixes the same in hot water." Today, I want to provide students with the opportunity to extend their learning by completing a similar investigation using hot, warm, and cold water. This will further support the challenging scientific idea that "matter is made of particles too small to be seen." (5-PS1-1)

Matter Unit Lapbooks

To provide students with a method to keep track of their research and thinking during our unit on matter, I followed these steps to create lapbooks for each student. 

1. I folded each side of a file folder inward to create a booklet that opens from the center: File Folder.

2. Next, I made copies of Lapbook Templates on colored paper (purple, yellow, green, and orange). I made sure to have enough copies so that each student would have 4 graphs, 6 research notes, 8 investigations, 18 vocabulary words (9 sets of 2 words), and the 4 pictures.  I also copied the Other Research Pocket onto blue card stock paper so that students would have a place to put loose papers. 

3. Then, I stapled the templates into each lapbook: Inside the Lapbook.

4. Before starting our unit on matter, I asked students to help personalize their lapbooks. Students used a glue stick and tape to secure the blue research pockets on the back (Student Research Pocket Example). Then, they decorated the cover: 


Creating these lapbooks helps build excitement and student ownership!

Vocabulary: Cohesion & Adhesion

To begin today's lesson, I review a couple of yesterday's water investigation tasks in order to introduce two new vocabulary words. I also use the following vocabulary poster to help students remember the definitions of the new vocabulary words using pictures: Cohesion & Adhesion Poster.

Cohesion: Do you remember when you placed a drop on your plastic mat yesterday and you tried to separate the drop into smaller drops? What happened? (The water molecules wanted to stick together instead of moving apart.) When water molecules are attracted to other water molecules, we call this cohesion!  

Adhesion: Yesterday, you also experienced adhesion. This is where the water molecules are attracted to other substances. Can anyone recall when water molecules stuck to other substances? (the water drop stuck to the end of the pipette, water drops sticking to the plastic mat, water drops still in the beaker when emptied)

After this discussion, students use the Cohesion & Adhesion Poster to add Cohesion and Adhesion to the vocabulary section of their lapbooks.

To encourage students to connection scientific concepts with their everyday lives, I ask students to share  examples of adhesion or cohesion: Discussing Cohesion & Adhesion.


I want to inspire interest in today's lesson and capitalize on student curiosity, so I invite students to the back table so I can demonstrate the movement of molecules using another model. Prior to the lesson, I gather a can of evaporated milk (Fresh milk may work better. This is what I had on hand!), food coloring, and dish soap: Milk Demonstration. Here's what the milk looked like after about ten minutes: Milk & Food Coloring After 10 Minutes.


40 minutes

Set Up

For today's investigation, students will have three jars of water (hot, warm, & cold). They will then add five drops of blue and five drop of red food coloring to each jar at the same time. Then, they will use a timer to determine the times in which the food coloring completely mixes in each temperature of water (making the water purple). 

Teacher Note: If I had the opportunity to teach this lesson again, I would have had students add 10 drops of each color (or maybe even more) so that the water very clearly changes to a deeper shade of purple. 

Prior to the lesson, I set out the following materials: 


Vocabulary: Diffusion

To introduce today's investigation, I want to introduce one more vocabulary word! Holding up a beaker of water, I add several drops of food coloring. What happened yesterday when you added food coloring to a beaker of water? (The food coloring mixed with the water due to the moving molecules.) Referring to the Diffusion Poster, I explain: Diffusion is the process by which molecules mix due to their motion. After students add Diffusion to the vocabulary section of their lapbooks, I continue: We are going to complete another investigation involving diffusion today. Would anyone like to share a question you are interested in investigating? Here are a few student responses: Student Questions

Teacher Note: NGSS Standard 5-PS1-1 states, "Develop a model to describe that matter is made of particles too small to be seen." While this standard does not address cohesion (the sticking together of water molecules), adhesion (water molecules sticking to other substances), and diffusion (water molecules mixing due to their motion), understanding the behaviors of molecules helps students prove the actual presence of molecules. 

Setting up the Investigation 

As a class, we complete the top portion of an investigation template in student lapbooks: Question & Observations (Before). We start with the question: How does the temperature of water affect the movement of molecules?

Then, we discuss how to set up the investigation (Investigation) and draw a diagram in the "Observations (Before)" box. What do we need to do to investigate this question? (Set up three glasses of water, cold, warm, & hot. Add three drops of red and blue food coloring to each jar. Start the stop watch.)

What are some of the controlled variables in this investigation? What do we want to keep the same in order to make sure we are conducting a fair test? Student responses include: 

  • Same amount of water (1 cup in each glass)
  • Same type of container
  • Same food coloring
  • Same thermometer

What variable do we want to change during this investigation? (Different temperatures of water water) We discuss how to properly use the thermometer to determine the temperature of each glass of water using degrees Fahrenheit. 

Before students begin the investigation, we discuss the Observations (After) & Conclusion sections of the investigation template. What do you want to observe? (how the food coloring mixes, the amount of time it takes for each glass of water to turn purple) After you have completed the investigation, how might you begin your conclusion? (I can conclude that...)

Monitoring Student Understanding

Once students collect supplies and begin investigating, I conference with every group. My goal is to support students by asking guiding questions (listed below). I also want to encourage students to engage in Science & Engineering Practice 7: Engaging in Argument from Evidence

  1. What patterns have you noticed? 
  2. Why do you suppose ____? 
  3. What have you found so far? 
  4. Has your thinking changed? 
  5. What evidence do you have? 
  6. How did you decide _____?
  7. What conclusion can you draw about ____?

Student Conference

Here, Students Investigating, students observe that the hot water is mixing more than the cold water. I encourage them to draw a conclusion based upon their observations. 

Student Work

Here are a couple examples of completed student investigation templates. Some students used the backside to continue their conclusions: 


Reflect & Apply

30 minutes

Sharing Findings

Now that students have built meaning and understanding by observing, questioning, and exploring, it is important to provide students with the opportunity to share their findings. For this reason, I invite students to read their conclusions out loud to the rest of the class.  

Here's an example of a student sharing her conclusion: Student Sharing Conclusion 1. Often times, sharing out loud helps inspire other students that might be struggling to construct evidence-based conclusions.