Introduction to Gas Laws (Exploration of Gas Concept/Extension of Stoichiometry)

Lesson Files for Download: https://drive.google.com/drive/folders/1R3k8LsUSWtGuES2FWWONs7ttQ\_w7vpxp?usp=sharing

This lesson is intended to be used to teach the connection between Gas Properties and stoichiometry. Students should do this assignment as a connection between Stoichiometry and Gas Laws. While some instructors teach these concepts as separate units, the 5E methodology pushes us to connect these themes as closely as possible, so students can draw on their existing knowledge and fit new knowledge into a sound schema. This 5E Unit plan is designed to feed into Thermodynamics, where students can calculate heat transfers and gas compression/expansion work.

### Prerequisites:

1. Mole Concept/Stoichiometry (mass-to-mass)
2. Dimensional Analysis/Algebra
3. Phases of Matter

### Standards Targeted (AZ State Science Standards)[1]

- PlusHS.Chem.P1U1.3: I can analyze and interpret data to develop and support an explanation for the relationships between kinetic molecular theory and gas laws

- PlusHS.Chem.P1U1.5: I can plan and carry out investigations to test predictions of the outcomes of various reactions, based on patterns of physical and chemical properties.

- PlusHS.Chem.P1U1.7: I can use mathematics and computational thinking to determine stoichiometric relationships between reactants and products in chemical reactions.

## Engage

###### Anchoring Phenomenon: Combustion reactions allows for cars to overcome friction and for rockets to overcome the force of gravity. You will explore how gases can do work, exert force, and connect the molecular world of chemistry to the mechanical world of physics.

NOTE: Gas Laws are best introduced with demonstrations. The more examples students can draw on, the quicker students will learn the relationships between moles, volume, pressure, and temperature. Also, practice the demos multiple times before showing students. They are a bit more tricky and specific than you'd think. Work out the kinks the weekend before with friends and/or family!

List of Demos: https://chemdemos.uoregon.edu/Topics/Gas-Laws.

## Explore and Explain

### 1. Review Stoichiometry and New Conversion Factors

Students will get comfortable with the collaborative group setting as they work through stoichiometry. I recommend reviewing stoichiometry and playing a "relay" game. I, John Borja, did NOT invent this game, nor the assignment, but I will be sharing the link to access it in the drive folder above.

### 2. DON'T POP IT! (Explore -> Explain)

In this phase, students will fill a Ziploc with Carbon Dioxide, produced from the reaction of baking soda and vinegar. This is the same chemical reaction students will use during the Elaboration/Evaluation section. Students will keep a log for their trials, including their qualitative observations, plans for improvement, and stoichiometry for determining quantities of reactants. This log pushes students to explain their results and hypothesize how they will address them in the future. In this process, students will gain firsthand experience with reaction rates, the effects of temperature, pressure, and volume on the behavior of gases, and the connection between gas laws and stoichiometry.

NOTE: Students will use the conversion factor of 22.4 L/mol gas to convert between the target volume of CO2 and the corresponding number of moles. The assumption of STP exaggerates the effects of temperature, pressure, and volume on the gas behavior. Student frustration with the inconsistencies of the aforementioned conversion factor opens the door to teaching PV = nRT to advanced groups of students.

## Elaborate

Students will use the same reaction of baking soda and vinegar to create a rocket that must travel 3 meters above the ground (approximately the height of a field goal base). Students will continue to log their results, although they will be responsible for organizing this information into a digestible and logical format. Students are also exposed to the full PV = nRT equation, which was not given in the Explore/Explain section. They will use this equation in conjunction with stoichiometry to build a target pressure within the bottle and harness it to achieve liftoff.

Note: This lesson can be referenced later in the year within a unit on thermodynamics: pressure-volume work in a piston is remarkably similar to the work done in the baking soda/vinegar reaction.

## Evaluate

Just as the student journal helps students to organize their thoughts and to continue making progress, it also serves to help students to reflect upon their knowledge and to update it with experience. Students are charged with monitoring their own progress and evaluating their contributions. The emphasis on student accountability enables students to become more independent and meta-cognizant, thereby pushing students to higher levels of critical thinking and lifelong learning.

**Advice from the instructor:**

1. **Standardize water bottle volume.** Larger bottles require up to six-times as much reactant in order to fill. Make sure students use 500 mL bottles. It makes the stoichiometry easy, and it reduces waste.
2. **Provide students with a pre-determined quantity of vinegar and baking soda** to ensure that they do not waste any. If they require extra reactant, you will have to determine whether you want students to donate/provide vinegar themselves or if you will continue providing the reactants. ADVANCED PLANNING IS NECESSARY!
3. **Do not allow students to use purchase additional materials, such as Lego Sets, Estes rockets, or other paid materials.** Some students will have certain financial advantages that could make the assignment much easier or harder. To keep project timing and outcomes consistent, preclude students from purchasing additional materials. Special accommodations may be necessary.
4. **Limit the amount of time students have to build rockets to two days.** If students spend more than two days building rockets, they will not be focused on the core ideas. Otherwise, they will be distracted by the insignificant nuances of design rather than maximizing their success elsewhere.
5. **Have students grade themselves daily.** If students give themselves a score from 1-5 and explain their reasoning, they are inclined to think critically about their own contributions to the group. If it is not graded, the effect is greater, since students are more likely to answer honestly and take action based on this reflection. For new 5E teachers, this type of self-accountability is a MUST. One student cannot carry the weight of the group, and the self grade helps mitigate this risk.