1. Carbon: Transformations in Matter and Energy
Environmental Literacy Project Michigan State University
Systems and Scale Unit Activity 3.4 Molecular Models for Soda Water Fizzing
Image Credit: Craig Douglas, Michigan State University
Prepare one model kit for each pair of students. Print one copy of the Molecular Models 11 x 17 Placemat and one copy of the 3.4 Molecular Models for Soda Water Fizzing Worksheet for each pair of students. Prepare a computer and a projector to display the PPT.

2. How Atoms Bond Together in Molecules
Atoms in stable molecules always have a certain number of bonds to other atoms:
Carbon: 4 bonds
Oxygen: 2 bonds
Hydrogen: 1 bond
Oxygen atoms do NOT bond to other oxygen atoms if they can bond to carbon or hydrogen instead.
Show students slide 2 to explain the bonding of atoms in molecules. Tell students that the rules on this slide are important because they apply to all molecules that they will make in all Carbon TIME units.

3. Making the Reactant Molecules: Carbonic Acid
The “fizz” and the taste of soda water come from carbonic acid: H2CO3. Make a molecule of carbonic acid on the reactant side of your Molecular Models Placemat:
Get the atoms you will need to make your carbonic acid molecule. Can you figure out from the formula for carbonic acid how many C, H, and O atoms you will need?
Use the bonds to make a carbonic acid molecule. Remember the rules for making stable molecules! (Hint: you will need to make one double bond to make a stable molecule.)
Compare your molecules to the pictures on the next slide. Are they the same?
Use Slide 3 to show instructions to construct a molecule of carbonic acid. Students can also follow instructions in Part A of their worksheet.

4. Photo of reactant molecule: H2CO3 (carbonic acid)
Chemical change
Photo Credit: Michigan State University
Use Slide 4 to instruct students to compare their own molecule with the picture on the slide.
Reactants
Products

5. Important:
When you are finished constructing the reactants, put all extra pieces away.
Slide 5 shows an important message: after students create their reactant molecules, make sure they put away all unused pieces of their molecule kits. This helps reinforce that the matter and energy in the reactants are conserved through the chemical change, and that only the materials from the reactants are used to build the products.

6. Rearranging the Atoms to Make Product Molecules: Carbon Dioxide and Water
Soda water loses its “fizz” when carbonic acid (H2CO3) breaks down into carbon dioxide (CO2) and water (H2O). Show how this can happen:
Break some of the bonds in your carbonic acid molecule and rearrange the atoms to make two new molecules: CO2 and H2O. Remember the rules for making stable molecules! (Hint: you will need double bonds to make stable molecules of CO2.)
Remember, atoms last forever. So you can make and break bonds, but you still need the same atoms.
Compare your molecules to the pictures on the next slide. Are they the same?
When soda water sits in the open, a chemical process occurs. Releasing the pressure on the soda water and allowing it to warm up allows the carbonic acid to decompose into carbon dioxide (CO2) and water (H2O).
Show slide 6 of the PPT and have students re-arrange the atoms to make molecules of CO2 and H2O. To do this, they will need to move their molecules from the Reactants side to the Products side of the 11 x 17 Placemat. Explain to students that atoms last forever, so they should not add or subtract atoms when they change the reactant molecule into product molecules.

7. Photo of product molecules: H2O (water) CO2 (carbon dioxide) Start by making the molecules and energy units of the reactants and putting them on the reactants side, then rearrange the atoms and energy units to show the products.
Chemical change
Photo Credit: Michigan State University
Show students Slide 7 to compare the products and a comparison between reactants and products.
Reactants
Products
Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can’t add or subtract atoms). Energy lasts forever (so you can change forms of energy, but energy units can’t appear or go away)

8. Comparing photos of reactant and product molecules Start by making the molecules and energy units of the reactants and putting them on the reactants side, then rearrange the atoms and energy units to show the products.
Chemical change
Photo Credit: Michigan State University
Show students Slide 8 to compare the molecules they made to the molecules on the slide.
Reactants
Products
Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can’t add or subtract atoms). Energy lasts forever (so you can change forms of energy, but energy units can’t appear or go away)

9. What happens to atoms when soda water decomposes?
Carbon Dioxide
Products
Chemical change
Credit: Craig Douglas, Michigan State University
Show slides 9-13 in the PPT to encourage students to make connections between what is happening in the animation and the molecular models they made.
For each slide, focus on different atoms in the molecule. The animation draws attention to where they atoms begin and end in the reaction.
Carbonic Acid
Reactants
Water

10. What happens to carbon atoms when soda water decomposes?
Carbon Dioxide
Products
Chemical change
Credit: Craig Douglas, Michigan State University
Show slides 9-13 in the PPT to encourage students to make connections between what is happening in the animation and the molecular models they made.
For each slide, focus on different atoms in the molecule. The animation draws attention to where they atoms begin and end in the reaction.
Carbon atoms in soda water become part of carbon dioxide molecules.
Carbonic Acid
Reactants
Water

11. What happens to oxygen atoms when soda water decomposes?
Carbon Dioxide
Products
Chemical change
Credit: Craig Douglas, Michigan State University
Show slides 9-13 in the PPT to encourage students to make connections between what is happening in the animation and the molecular models they made.
For each slide, focus on different atoms in the molecule. The animation draws attention to where they atoms begin and end in the reaction.
Focus on oxygen atoms
Oxygen atoms in soda water become part of water and carbon dioxide molecules.
Carbonic Acid
Reactants
Water

12. What happens to hydrogen atoms when soda water decomposes?
Carbon Dioxide
Products
Chemical change
Credit: Craig Douglas, Michigan State University
Show slides 9-13 in the PPT to encourage students to make connections between what is happening in the animation and the molecular models they made.
For each slide, focus on different atoms in the molecule. The animation draws attention to where they atoms begin and end in the reaction.
Focus on hydrogen atoms
Hydrogen atoms in soda water become part of water molecules.
Carbonic Acid
Reactants
Water

13. What happens to atoms when soda water decomposes?
Carbon Dioxide
Products
Chemical change
Credit: Craig Douglas, Michigan State University
Show slides 9-13 in the PPT to encourage students to make connections between what is happening in the animation and the molecular models they made.
For each slide, focus on different atoms in the molecule. The animation draws attention to where they atoms begin and end in the reaction.
Focus on the Rule that “Atoms last forever”
Atoms last forever!
Carbonic Acid
Reactants
Water

14. Writing a Chemical Equation
Chemists use chemical equations to show how atoms of reactant molecules are rearranged to make product molecules
Writing the equation in symbols: Chemists use an arrow to show how reactants change into products: [reactant molecule formulas] product molecule formulas]
Saying it in words: Chemists read the arrow as “yield” or “yields:” [reactant molecule names] yield [product molecule names]
Equations must be balanced: Atoms last forever, so reactant and product molecules must have the same number of each kind of atom
Try it: can you write a balanced chemical equation to show the chemical change when soda water loses its fizz?
Show Slide 14 of the presentation to guide students through the process of writing a balanced chemical equation for the decomposition of carbonic acid. Indicate that the decomposition of carbonic acid is a chemical reaction and that the chemical equation is a representation of this reaction. Tell students that these rules apply to all chemical reactions.
Tell students to write their equations in Part C of their worksheet.
Have students write their own chemical equations before comparing them with the one on Slide 15.

15. Chemical equation for soda water losing its fizz
H2CO3  H2O + CO2 (in words: carbonic acid yields water and carbon dioxide)