Activity 4.4 - Molecular Models for Ethanol Burning (50 min)

Target Student Performance

Students use molecular models to explain how carbon, oxygen, and hydrogen atoms are rearranged into new molecules during the oxidation of ethanol (the chemical change that happens when ethanol burns).

Resources You Provide

molecular model kit (1 per pair of students)
scissors (1 per pair of students)
twist ties (at least 12 per pair of students)

Resources Provided

4.4 Molecular Models for Ethanol Burning Worksheet (1 per student)
4.4 Grading the Molecular Models for Ethanol Burning Worksheet
4.4 Molecular Models for Ethanol Burning PPT
4.4 Molecular Models for Ethanol Burning Reading (1 per student)
4.4 Alternative Flame Molecular Model Placemat (1 per pair of students)
Carbon TIME Molecular Modeling Ethanol Video

Recurring Resources

Learning Tracking Tool for Systems and Scale (1 per student)
Assessing the Learning Tracking Tool for Systems and Scale
Questions, Connections, Questions Student Reading Strategy
Forms of Energy Cards (1 set pair of students)
Molecular Models 11 x 17 Placemat (1 per pair of students)

Setup

Prepare one model kit, one Molecular Models 11 x 17 Placemat, one pair of scissors, and one Forms of Energy Cards for each pair of students. Print one copy of the 4.4 Molecular Models for Ethanol Burning Worksheet and 4.4 Molecular Models for Ethanol Burning Reading for each pair of students. Prepare a computer and a projector to display the PPT.

Directions

1. Use the instructional model to show students where they are in the course of the unit.

Show slide 2 of the 4.4 Molecular Models for Ethanol Burning PPT.

2. Have students read Molecular Models for Ethanol Burning Reading.

Display slide 3 of 4.4 Molecular Models for Ethanol Burning PPT. Give each student a copy of 4.4 Molecular Models for Ethanol Burning Reading.

Remind students that the investigation left them with unanswered questions (students can refer back to 4.3 Evidence-Based Arguments Tool for Ethanol Burning).
Have students read 4.4 Molecular Models for Ethanol Burning Reading to learn about modeling using the Questions, Connections, Questions Student Reading Strategy. See the Engaging Students with Readings and the Questions, Connections, Questions Reading Strategy Educator Resource document for information about how to engage students with this strategy.
Have a class discussion about why scientists use molecular models and about why they need to use molecular modeling to answer their unanswered questions.

3. Zoom into a flame.

Display slide 4 from the 4.4 Molecular Models for Ethanol Burning PPT to explain molecular bonding to students.

Pose the question: “What’s the hidden chemical change when ethanol burns?” Explain to students that both ethanol and O₂ enter the flame at the bottom. Ethanol enters the flame through evaporation. Write the chemical formula for ethanol on the board, “C₂H₅OH” This means each ethanol molecule has two carbons, six hydrogens and one oxygen atom.
Show slides 5 and 6 to contrast the molecules at the bottom and top of a flame.

4. Have students use the molecular model kits to make one ethanol and three oxygen molecules.

Divide the class into pairs and give each pair a molecular model kit, a set of Forms of Energy Cards, and Molecular Models 11 x 17 Placemat. Pass out one copy of 4.4 Molecular Models for Ethanol Burning Worksheet to each student.

Show students slide 7 to remind them of how atoms bond in molecules. These rules apply to all molecules that they will make in all Carbon TIME units.
Use slide 8 to show instructions to construct oxygen and ethanol molecules. Students can also follow instructions in Part B of their worksheet.
Use slide 9 to instruct students to compare their own molecule with the picture on the slide.
Use slide 10 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.

Accommodation: Arrange the molecules along with students so they have a step-by-step model of what the molecules should look like.

Use the Carbon TIME: Molecular Modeling Ethanol Video if doing in-person molecular modeling is not possible, or to support absent students.

5. Have students complete the table their worksheet for the reactants.

When they have completed their reactants, tell students to complete the table about matter and energy in their worksheet for the reactants.

Use the Carbon TIME: Molecular Modeling Ethanol Video if doing in-person molecular modeling is not possible, or to support absent students.

6. Have students watch an animation of the chemical change.

Show slides 14-19 in the PPT to help students make connections between what is happening in the animation and the molecular models they made.

For each slide, focus on different atoms and forms of energy and how they change. The animation draws attention to where they atoms begin and end in the reaction.

7. Have students record their results.

Show slide 20 in the PPT.

Tell students to complete Part C of their worksheet to trace the atoms during the chemical change.

8. Have students record their results.

Show slide 21 in the PPT.

Tell students to complete Part D of their worksheet to trace the energy during the chemical change.

9. Discuss results with the class.

Show slide 22 in the PPT.

Complete the “check yourself” questions with the class in Part E.

10. Help students write a balanced chemical equation on the worksheet.

After the discussion, tell students that now that they have represented a chemical change using molecular models and in animations, they will represent chemical change by writing the chemical equation.

Show Slide 23 of the presentation to guide students through the process of writing a balanced chemical equation for the combustion of ethanol. Tell students that these rules apply to all chemical reactions.
Tell students to write their equations in Part F of their

Have students write their own chemical equations before comparing them with the one on Slide 24.

Assessment

Listen for the students’ sense of necessity to make sure that atoms last forever during chemical changes. Asking them about the “atoms are forever” rule during the molecular modeling and animation may give you a sense of how committed they are to conserving matter.

Differentiation

Instead of the Molecular Models 11 x 17 Placemat, provide your students with the 4.4 Alternative Flame Molecular Model Placemat to use as the placemat for their molecular modeling. Have students place the models in the appropriate locations on the flame system placemat before, during and after the chemical change.

Modifications

Tips

Laminate the Molecular Models 11 x 17 Placemat. These will be used multiple times in each unit.
During the molecular modeling activity and animation, focus on how matter and energy are conserved through the chemical change. This is the main goal of the activity!

Extending the Learning

Lesson 5 will include opportunities for students to learn about the combustion of other fuels, including methane, propane, and octane. Curious students can look up the formulas for these fuels and make molecular models of them.