Chemical Reactions

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Objective

SWBAT prove that even though new substances are produced during chemical reactions, the beginning and ending mass/weight stays the same.

Big Idea

In this lesson, students examine how mixing baking soda and vinegar results in new substances. They also discover that the beginning and ending mass of this chemical reaction remains the same.

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 introducing the Law of Conservation using a class poster. Students then explore how mixing baking soda and vinegar creates new substances. They also learn that the beginning mass of the baking soda and vinegar is equal to the ending mass of their products. At the end of the lesson, students reflect and apply their new understanding of the Law of Conservation by writing an evidence-based summary. 

Next Generation Science Standards  

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

5-PS1-2. Measure and graph quantities to provide evidence that regardless of the type of change that occurs when heating, cooling, or mixing substances, the total weight of matter is conserved.

5-PS1-4. Conduct an investigation to determine whether the mixing of two or more substances results in new substances.

Scientific & Engineering Practices

For this lesson, students are engaged in Science & Engineering Practice:

Science & Engineering Practice 1: Asking Questions and Defining Problems 

Students explore whether or not the Law of Conservation applies to chemical reactions. 

Crosscutting Concepts

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

Crosscutting Concept 4: Systems and System Models 

Students use a closed system model to make sure they capture all of the products of a chemical reaction. 

Crosscutting Concept 5: Energy and Matter

Students examine the Law of Conservation by tracking matter before and after processes. The recognize that the total mass/weight does not change during physical and chemical changes. 

Disciplinary Core Ideas

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

PS1.B:  Chemical Reactions

When two or more different substances are mixed, a new substance with different properties may be formed. (5-PS1-4)

No matter what reaction or change in properties occurs, the total weight of the substances does not change. (Boundary:  Mass and weight are not distinguished at this grade level.) (5-PS1-2)

ELA Integration

To add depth to student understanding, when I can, I'll often integrate ELA standards with science lessons. Today, students will work on meeting CCSS.ELA-LITERACY.W.5.2: Write informative/explanatory texts to examine a topic and convey ideas and information clearly. In this lesson, students will write an explanatory text to examine how the Law of Conservation applies to various processes. 

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!   

Focus

40 minutes

Teacher Note: This is a lengthy lesson that can be separated into two lessons! 

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!

Law of Conservation Poster

Today is the perfect day to introduce the Law of Conservation to students. So far, students have learned that the mass of matter stays the same during physical changes (when the shape changes, when the temperature changes, and when matter is mixed). Today, we will be investigating how the mass of matter also stays the same during a chemical reaction. But first, we will apply the Law of Conservation to the investigations we have already completed by creating a class poster. Here's what the poster will look like at the end of the lesson  Completed Law of Conservation Poster. At the beginning of the lesson, we will only complete part 1: Law of Conservation Poster (Part 1).

I begin by passing out a sheet of green paper to each student. I explain: Today, we are going to make a class poster on the Law of Conservation. (I write Law of Conservation in the center of the the poster). I'm passing this green paper out so that you can make your own posters at the same time. 

Meaning of Conserve

Before we begin, please work with your elbow partner to look up the word, conserve, in a dictionary. What does it mean? A student shares his findings, "Conserve means to prevent the waste of something." We add this to our posters. 

Meaning of Mass

Then, we review the word, mass. I write on the poster as a student recalls the meaning of mass from past lessons, "Mass is the measurement of matter." I then add on: matter refers to the amount of "stuff" in something.

The Law of Conservation

I continue on by taking notes and explaining at the same time: The Law of Conservation of Matter states that mass/matter can't be created and mass/matter can't be destroyed. When making changes to matter, the mass stays the same... as long as you don't add or take away anything and as long as you have a closed system.

Examples of Physical Changes

To help students make sense of this new scientific concept, I don't waste any time connecting it to familiar examples of physical changes. I also draw labeled pictures to add interest.

  • When we changed the shape of clay to a ball, flat, and a roll, the mass stayed the same. 
  • When we changed the temperature of ice, the mass stayed the same.
  • Finally, when we mixed gravel and sand together, the ending mass was the same as the beginning mass of the gravel and sand combined. 

 

Discussing Chemical Changes

Now that we've discussed how the Law of Conservation works with physical changes, what question are you pondering? Amazingly, a student raises her hand and asks, "Does the Law of Conservation apply to chemical reactions?" We add this final thought to our posters. After completing today's investigation, we'll return to answer this student's question. This is a perfect segway into the exploration part of this lesson. 

Explore

50 minutes

Teacher Note: For the exploration portion of this lesson, students will investigate the reaction between baking soda and vinegar. To align with NGSS Standard 5-PS1-2 (No matter what reaction or change in properties occurs, the total mass/weight of the substances does not change.), students will find the mass of the substances before and after they are mixed. 

I also want to align this lesson with NGSS Standard 5-PS1-4, (Conduct an investigation to determine whether the mixing of two or more substances results in new substances). For this reason, before investigating, we will discuss and find the pH levels of baking soda, vinegar, and the product of baking soda and vinegar. This will help students realize that the mixture of these two substances results in new substances. 

Getting Ready

To prepare for today's investigation, I set out the following items on the counter: 

*The cups for this investigation are the small Dixie cups. I made sure that they were less than half full of baking soda and vinegar. Too much baking soda and vinegar will cause the bags to pop during the investigation. 

Today, each group will be mixing baking soda and vinegar to investigate a chemical reaction. What is a chemical change again? Reflecting on our Physical & Chemical Changes Poster, students recall that a chemical change is when matter changes on a molecular level, resulting in the formation of a new substance. In order to prove that this is truly a chemical reaction and that new substances are formed, we are going to first take a look at a scientific tool called the pH scale.

Finding the pH Levels of Substances

I invite students to turn to the last picture in our lapbook, the pH scale: 

Image Source: https://upload.wikimedia.org/wikipedia/commons/4/46/PH_scale.png 

Using a Teacher Model, we write a caption and label the picture: Scientists use the pH scale to measure how acidic or basic a substance is. When you mix baking soda and vinegar, they neutralize each other. The pH level of water is 7, which is neutral. The pH levels below 7 are acidic and above 7 are basic. Can anyone find vinegar? Vinegar has a pH level of 3. Is vinegar acidic or basic? (acidic) Can anyone find baking soda? Baking soda has a pH of 8. Is baking soda acidic or basic? (basic) Here's a Student Example of Caption for the pH Scale.

I set out cabbage juice, a pH color scale, a cup of baking soda, and a cup of vinegar (Teacher pH Scale Demonstration), to demonstrate how to find the pH levels of substances. (When cabbage juice is added to a substance, the resulting color indicates a pH level.) After adding a few drops of cabbage juice to the vinegar, the vinegar turns red, indicating that it truly does have a pH of 3. Then we checked the pH of baking soda. Students predict that it will turn blue to indicate a pH of 8. They are right! Next, I put on my goggles (modeling safety!) and mix the baking soda and vinegar. The result turns purple: Ph Level After the Reaction. We discuss how this provides evidence that new substances are formed when baking soda and vinegar are mixed. The two substances neutralize each other and produce a product that has a pH level of 7. 

Soon, almost the whole class is at my front desk, excitedly asking if we can test the pH levels of different substances throughout the room! We end up testing hand sanitizer, rubbing alcohol, hydrogen peroxide, soap, spit, multi-purpose cleaner, and a cracker! Student responses were so fun to listen to: "Whoa!" "Cool!" "That's awesome!" 

This pH scale demonstration really gets students thinking about science! One student raises her hand to ask a great question: Student Question.

Investigation Template

The class discusses and completes a new investigation template in their lapbooks. I model their thinking by projecting the following Teacher Model of Investigation.

Question: When there is a chemical reaction between baking soda and vinegar, does the mass change? 

Today, you will each be given a Ziplock bag, one cup of baking soda, one cup of vinegar, and a pair of safety goggles for each student. First, I'd like for you to very carefully place the cups of baking soda and vinegar in the bag, side-by-side. Then, we will seal the bag shut so that we have a closed system (Placing the Cups in the Tightly Sealed Bag).

What will we need to do in order to answer our investigation question? (Find the mass of the bag Before the Reaction and After the Reaction). 

Observations (Before): Students observe that there's one cup of vinegar and one cup of baking soda placed in a sealed bag, creating a closed system. 

Observations (After): To prepare for recording investigation data, we draw a data table to collect the mass of the bag before and after the reaction.

I provide some final directions before students start investigating. 

  • Make sure to wear your safety goggles at all times. (Now looking back at my videos of this lesson, I realize that many students forgot this step.)
  • There are 3 Digital Scales throughout the room. Please use the digital scale closest to your group when finding the mass before and after the reaction. 
  • After placing the cup of baking soda and cup of vinegar in the bag, try to get as much air out as possible before sealing it. Once it is sealed, you will not be opening the bag again today.
  • When you are ready, without opening the bag, carefully pick up the cup of vinegar and dump it into the cup of baking soda (Students Pouring the Vinegar into the Baking Soda Cup).
  • No matter what, DON'T OPEN THE BAG! 

 

Students Investigating

Here, students very carefully walk their sealed bags over to the nearest digital scale to find the mass: Students Find the Mass Before the Reaction. The mass of most student bags is under 100 grams. 

Now, for the exciting part: Students Mix the Substances! In this video, a student comments on how he doesn't think the mass will change. I love how he applies what he already knows about the Law of Conservation and his experiences with the mass before and after physical changes (such as the shape of clay) and says, "Because you're taking nothing away from it." 

Reflect & Apply

50 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 share what they have found: 

  • Our bag had a mass of 99 grams before the reaction and 98 after the reaction. (We discuss how these measurements are about the same and how the placement of the bag on the scale or a leaky bag could affect the end results.)
  • The reaction bubbled and the bag filled up with air. (We refer back to the definition of a chemical reaction - when substances are mixed, resulting in the formation of a new substance. We discuss how the carbon dioxide in the bag is evidence of a new substance being formed.)

 

Writing Conclusions

The class takes a few minutes to complete the conclusion section of their investigation template (Chemical Reaction Student Investigation). As students finish, I ask them to turn and share their conclusions with their elbow partners. We don't spend a lot of time on this as I want the students to have enough time to write an explanatory paragraph on the Law of Conservation. 

Law of Conservation Poster

Returning to the Law of Conservation Poster, we answer the question, "Does the Law of Conservation apply to chemical reactions?" We review the outcome of our baking soda and vinegar reaction and how the beginning mass was (about) equal to the ending mass. The class agrees that this is evidence that the amount of mass/matter stayed the same. 

I also write out the chemical formula for the reaction: NaHCO3 (baking soda) + HC2H3O2 (vinegar) = NaC2H3O2 + H20 + CO2.  We discuss: Even though new substances are formed, the same number of atoms are still present. There's still one Na atom (sodium), there are 5 hydrogen atoms, and 3 carbon atoms. This helps students see that matter is not created or destroyed, just rearranged. While teaching a chemical formula may seem a bit complex for 5th graders, most students caught on to the concept I was trying to teach. I love watching and listening to the students as they test the rule, the number of atoms you start with is equal to the number of atoms you end up with, to see if it always works. One student says, "It doesn't work with oxygen. There's 5 oxygen atoms to begin with and then 4 oxygen atoms at the end." Other students refer to the equation and respond, "No.... there's five at the end too. Look... two oxygen (NaC2H3O2) + one oxygen (H20) + two oxygen (CO2)." Then the first student says, "Oh yeah... now I see it!" 

Law of Conservation Paragraph 

To summarize today's learning, I pass out a lined sheet of paper to each student and provide the following Teacher Writing Prompt: The Law of Conservation is very interesting. I ask students to write a paragraph, explaining what the Law of Conservation is and how their investigations prove that the beginning mass and ending mass always stays the same with physical and chemical reactions. 

As students write, I invite them to share their paragraphs out loud to help support and inspire other students. This is also a great way to recognize students and to provide immediate feedback.

Here are a few examples of finished paragraphs: Student Paragraph Examples