(Optional) Lesson 3 - Investigating and Explaining Soda Water Fizzing

Overview

Students investigate changes in mass and CO₂ concentration for soda water fizzing. Then they explain results using molecular models and chemical equations to answer the Movement Question and the Matter Change Question.

Guiding Question

What happens when soda water loses its fizz?

Activities in this Lesson

Note: Lesson 3 is optional depending on
your knowledge of your students and learning goals. This lesson is recommended for middle schoolers to introduce them to using investigations, molecular models, and chemical equations to describe a simple chemical change. See the Systems and Scale Unit Read Me file for more information to consider when making this choice.

Activity 3.1: Predictions about Soda Water Fizzing (20 min)
Activity 3.2: Observing Soda Water Fizzing (30 min)
Activity 3.3: Evidence-Based Arguments about Soda Water Fizzing (45 min)
Activity 3.4: Molecular Models for Soda Water Fizzing (45 min)
Activity 3.5: Explaining Soda Water Fizzing (40 min)

Unit Map

Unit Map for Lesson 3

Target Performances

(Optional) Lesson 3 – Investigating and Explaining Soda Water Fizzing (students as investigators and explainers)
Activity 3.1: Predictions and Planning for Soda Water Fizzing (20 min)	Students develop hypotheses about how matter moves and changes when soda water loses its fizz and make predictions about how they can use their investigation tools—digital balances and BTB—to detect movements and changes in matter.
Activity 3.2: Observing Soda Water Fizzing (30 min)	Students record data about changes in mass and BTB when soda water fizzes and reach consensus about patterns in their data.
Activity 3.3: Evidence-Based Arguments about Soda Water Fizzing (45 min)	Students (a) use data from their investigations to develop evidence-based arguments about matter movements and matter changes when soda water fizzes, and (b) identify unanswered questions about matter movement and matter change that the data are insufficient to address.
Activity 3.4: Molecular Models for Soda Water Fizzing (45 min)	Students use molecular models to explain how carbon, oxygen, and hydrogen atoms are rearranged into new molecules during the decomposition of carbonic acid (the chemical change that happens when soda water fizzes).
Activity 3.5: Explaining Soda Water Fizzing (40 min)	Students explain how matter moves and changes when soda water loses its fizz (connecting macroscopic observations with atomic-molecular models and using the principle of conservation of matter).

NGSS Performance Expectations

Middle School

Structures and Properties of Matter. MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures.
Chemical Reactions. MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
Chemical Reactions. MS-PS1-5. Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.

High School

Chemical Reactions. HS-PS1-7. Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Three-dimensional Learning Progression

This lesson (which is optional for high school students) uses a simple chemical change, the decomposition of carbonic acid, to introduce students to using investigations, molecular models, and chemical equations to describe chemical changes.

Carbonic acid is a weak acid, meaning that it always exists in equilibrium with dissolved CO₂ in water, which in turn is in equilibrium with gaseous CO₂ in the air. Increasing temperature and decreasing pressure drive the equilibrium in the direction of gaseous CO₂, so when the soda water “loses its fizz,” carbonic acid is dissociating, and dissolved CO₂ is escaping into the air.

In this lesson students are introduced to two of the Three Questions. All Carbon TIME Units share a focus on understanding the chemical changes involved in complex processes, such as combustion and growth of plants and animals. We will consistently focus on the idea that understanding these processes involves answering Three Questions:

The Matter Movement Question: Where are molecules moving? (How do molecules move to the location of the chemical change? How do molecules move away from the location of the chemical change?)
The Matter Change Question: How are atoms in molecules being rearranged into different molecules? (What molecules are carbon atoms in before and after the chemical change? What other molecules are involved?)

Matter (the Matter Movement and Matter Change Questions). We find that even students who have learned how to balance chemical equations do not appreciate the meaning of the procedure:

Conservation of atoms (the Matter Change Question): The numbers of atoms on the left and right side of a chemical equation have to be the same because they are THE SAME ATOMS! A chemical equation just shows how they are being rearranged into new molecules.
Conservation of mass (the Matter Movement Question): ALL the mass of any material is in its atoms (and none of the mass is in the bonds, which are just attractive forces between atoms). So the mass of the products is always the same as the mass of the reactants.

In this lesson, students will focus only on two: The Matter Movement Question and the Matter Change Question. They turn to the Energy Change Question in the following lesson when they investigate burning ethanol.

The investigations in all units will make use of two essential tools:

Digital balances. Students can detect movement of atoms (the Matter Movement Question) by measuring differences in mass. In this activity students will be able to observe changes in the system of the soda water.
Bromothymol blue (BTB) is an indicator that changes from blue to yellow in response to high levels of CO₂. Thus changes in BTB can partially answer the Matter Change Question by detecting whether there is a chemical change that has CO₂ as a reactant or product.

Key Ideas and Practices for Each Activity

Activity 3.1 is the Predictions and Planning Phase of the instructional model (beginning the climb up the triangle). During this phase, students record their predictions and express ideas about what happens to matter when soda water fizzes. They use the Predictions and Planning Tool to do this.

Activity 3.2 is the Observations Phase of the instructional model (going up the triangle). During this phase, the students conduct the investigation for soda water fizzing, record data, and try to identify patterns in their data and observations. The important practices students focus on in this activity are 1) making measurements and observations, 2) recording their data and evidence, and 3) reaching consensus about patterns in results. They use the Observations Worksheet and Class Results Poster to do this.

Activity 3.3 the Evidence-Based Arguments Phase of the instructional model (going up the triangle). During this phase, the students review the data and observations from their investigation of soda water fizzing and develop arguments for what happened during the investigation. In this phase, they also identify unanswered questions: at this point they have collected data and observations about macroscopic scale changes (BTB color change and mass change), but they do not have an argument for what is happening at the atomic-molecular scale. They use the Evidence-Based Arguments Tool to record their arguments at this phase.

Activity 3.4 is the first part of the Explanations Phase of the instructional model (going down the triangle). Students construct molecular models of the chemical change they observed in the investigation to help them develop an atomic-molecular explanation for what happened.

Activity 3.5 the second part of the Explanations Phase of the instructional model (going down the triangle). Students use the Explanations Tool to construct final explanations of what happens when soda water fizzes. Ideally, at this phase their explanations will combine evidence from macroscopic-scale observations during the investigation with their new knowledge of chemical change at the atomic-molecular scale.

Key carbon-transforming processes: Decomposition of carbonic acid

Content Boundaries and Extensions

Talk and Writing

At this stage in the unit, students will complete the inquiry and application sequences for soda water fizzing—they go both up and down the triangle. This means that they will go through the Predictions Phase, the Observations Phase, the Evidence-Based Arguments Phase, and the Explanations Phase in one lesson. The tables below shows specific talk and writing goals for these phases of the unit.

Talk and Writing Goals for the Predictions Phase	Teacher Talk Strategies That Support This Goal	Curriculum Components That Support This Goal
Treat this as elicitation and brainstorming (like the Expressing Ideas and Questions Phase), but with more directed questioning.	Now that we have set up the investigation, we want to predict what we think will happen to matter and energy.	Predictions and Planning Tool
Elicit a range of student ideas. Press for details. Encourage students to examine, compare, and contrast their ideas with the ideas of other students.	Who can add to that? What do you mean by _____? Say more. So I think you said _____. Is that right? Who has a different idea? How are those ideas similar/different? Who can rephrase ________’s idea?	Investigation Video (first half)
Encourage students to provide evidence that supports their predictions. .	How do you know that? What have you seen in the world that makes you think that?
Have students document their ideas to revisit later.	Let’s record our ideas so we can come back to them and see how our ideas change.	Predictions and Planning Tool

Talk and Writing Goals for the Observations Phase	Teacher Talk Strategies That Support This Goal	Curriculum Components That Support This Goal
Help students discuss data and identify patterns.	What patterns do we see in our data? How do you know that is a pattern? What about ______ data. What does this mean?	Class Results Poster Class Results Spreadsheet
Encourage students to compare their own conclusions about the data and evidence with other groups and other classes.	What about this number? What does this tell us? How is group A’s evidence different from Group B’s data? How do our class’s data differ from another classes’ data?	Class Results Spreadsheet Class Results Poster Investigation Video (second half).
Make connections between the observations and the data/evidence.	It says here that our BTB turned colors. What does that mean? You recorded that your ethanol lost weight. What does that mean?
Have students consider how their predictions and results compare.	Let’s revisit our predictions. Who can explain the difference between our class predictions and our results? Who had predictions that were similar to our results? Has your explanation changed? How?

Talk and Writing Goals for the Evidence-Based Arguments Phase	Teacher Talk Strategies That Support This Goal	Curriculum Components That Support This Goal
Press for details. Encourage students to examine, compare, and contrast their ideas with the ideas of other students.	Who can add to that argument? What do you mean by _____? Say more. So I think you said _____. Is that right? Who has a different argument? How are those arguments similar/different? Who can rephrase ________’s argument?	Investigation Video (second half)
Students provide evidence from the investigation (not just experiences in the world) to develop arguments.	Does your argument include evidence from the investigation? What evidence is most important here? What does this evidence tell us about what happened? What evidence do we still need for a complete picture of what happened? How do you know that?	Evidence-Based Arguments Tool Class Results Poster Class Results Spreadsheets Investigation Video (second half) Data from other classes
Focus on how matter and energy were transformed at different scales.	What does this evidence tell us about how matter is changing? What does this evidence tell us about how energy is changing?	Evidence-Based Arguments Tool
Revisit predictions and examine change in thinking.	Let’s revisit our Predictions and see how our thinking changed now that we know what happened.	Evidence-Based Arguments Tool Predictions and Planning Tool
Encourage students to consider the questions they don’t have answers to.	This investigation told us many things about what happen to matter and energy during ____. But what questions do we still have?

Talk and Writing Goals for the Explanations Phase	Teacher Talk Strategies That Support This Goal	Curriculum Components That Support This Goal
Examine student ideas and correct them when there are problems. It’s ok to give the answers away during this phase! Help students practice using precise language to describe matter and energy.	Let’s think about what you just said: air molecules. What are air molecules? Are you talking about matter or energy? Remember: atoms can’t be created. So that matter must have come from somewhere. Where did it come from? Let’s look at the molecule poster again… is carbon an atom or a molecule?	Molecule Poster
Focus on making sure that explanations include multiple scales.	The investigation gave us evidence for what was happening to matter and energy at a macroscopic sale. But what is happening at an atomic-molecular scale? What is happening to molecules and atoms? How does energy interact with atoms and molecules during chemical change? Why doesn’t the macroscopic investigation tell us the whole story? Let’s revisit our scale poster… what is happening to matter at the molecular scale?	Molecular Models Molecular Modeling Worksheets Explanations Tool PPT Animation of chemical change Powers of Ten Poster
Encourage students to recall the investigation.	When did this chemical change happen during our investigation? How do we know that? What is our evidence? What were the macroscopic indicators that this chemical change took place?	Evidence-Based Arguments Tool Investigation Video
Elicit a range of student explanations. Press for details. Encourage students to examine, compare, and contrast their explanations.	Who can add to that explanation? What do you mean by _____? Say more. So I think you said _____. Is that right? How are those explanations similar/different? Who can rephrase ________’s explanation?	Explanations Tool