# CT-STEM

Stoichiometry - Creating A Fizzy Drink Part 1 - Preview

# Stoichiometry - Creating A Fizzy Drink Part 1

Subject: Chemistry
Time: 8 lessons = ~9 days (days are based on 50 min period length)
Level:

High School Honors Chemistry

## Unit Overview

This unit is not arranged as a traditional stoichiometry unit. Rather than beginning by stating the law of conservation of mass to students, it begins with an inquiry lab for students to discover that law. All quantities in this lab will be measured in grams. This will lead to a discussion of grams versus moles -- when each unit is appropriate and why. After students have developed this basic understanding, they will be presented with an in-class lab demonstration and subsequent simulation involving limiting reactants. Limiting reactants will be used to help students understand the most efficient ratios needed in a chemical equation that will produce maximum product. Students use this same logic and apply it in order to balance chemical equations.

Gapless Explanation of Anchoring Phenomenon (combination of Stoichiometry Part 1 & Part 2)

Can carbonation be introduced into a beverage without a gadget such as a sodastream? (A sodastream carbonates beverages by bubbling carbon dioxide directly into a beverage.) To carbonate a beverage in the classroom, two solid chemicals are mixed together to create the gaseous carbon dioxide, but this example reaction is not the only one that will produce carbon dioxide.

The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. Mass simply rearranges itself to form products. Thus, whatever mass we introduce as a reactant or reactants of a chemical reaction we will see that form the product or products. Quantities of solid chemicals in the laboratory are measured in grams. However, 1 gram of different chemicals or compounds does not contain the same number of atoms/particle units. The counting unit the mole is necessary to relate chemical compounds in an overall equation to each other and make sure amounts are comparable. One mole of a chemical or compound always contains the same number of atoms/particle units. Moles are also used to determine concentrations of aqueous solutions. Concentration is expressed as molarity (M) which is the number of moles of solute per liter of solution.

Reactant amounts in a chemical reaction should produce the maximum amount of desired product possible without leaving any excess reactants. Different reactants and products can only be compared if those amounts are in moles. The correct molar ratio for a chemical reaction is the ratio that will produce the maximum amount of product without any reactant going to waste. If an excess reactant remains after a chemical reaction occurs, then that ratio is not the correct one. Molar relationships lead to the idea of balancing equations. A balanced equation represents the correct molar ratio for an overall chemical reaction equation. When an equation is balanced, the same number of atoms (for a specific element) should be represented on the reactants and products side of the equation. A balanced equation represents atoms, but as the ratio of moles to atoms is the same for all elements, a balanced equation also represents moles.

If reactant quantities for a balanced chemical reaction are known, the theoretical yield of each product can be determined using dimensional analysis to complete stoichiometry calculations. In addition to determining theoretical yields, a limiting reactant and any amount of excess reactant can also be identified. This process can be applied and utilized to determine specific amounts of citric acid and baking soda that should be combined in a solution of Kool-Aid and sugar to carbonate the beverage and create soda pop. If incorrect amounts of either reactant are used, there will be excess reactant remaining which will affect the taste of the beverage.

The pre-assessment should be completed before beginning lesson 1 and should take approximately 50 minutes to complete. The post-assessment should be completed after lesson 8 and should also take 50 minutes to complete. The post assessment should be completed prior to beginning the second part of this unit (lessons 9-12).

This first part of this unit consists of 8 lessons (Part 1 & Part 2 = 12 total lessons). Lessons range from 50-100 minutes in length.

Part 1 Stoichiometry Unit: Lesson Outline

 Lesson Time Main activity that students are doing Big student takeaway Rationale 1: Phenomenon Introduction How can you carbonate a beverage without a sodastream at home? 50 mins Students watch commercial, hypothesize how sodastream operates. Then students watch instructional video on operation of sodastream and again hypothesize further about its operation. Students watch teacher demo of reaction (citric acid + baking soda) that produces carbonation describe how possible without sodastream. Gaseous carbon dioxide is what is used to carbonate a beverage. Carbon dioxide can be produced via a chemical reaction in the lab. Bubbles are evidence of a chemical reaction as they indicate that a gas was produced. The sodastream commercial is used here as this entire unit is based around carbonating a beverage. The unit will end with students performing an in-class lab practical where they carbonate Kool-Aid and then drink it. 2: Conservation of Mass What Happens to Mass During a Chemical Reaction? 100 minutes Students will perform simple chemical reactions. They will observe the reactions and record total mass of reactants and products for each reaction. They will be asked to share data with the class and compare their data to other student groups. Students will be probed to come up with the law on their own both from their data and prior knowledge. Students then watch a video about losing weight and are asked, “where does the mass go”? The Law of Conservation of Mass - Matter is not created or destroyed in a chemical reaction, but it can be rearranged in space and change states. The law of conservation of mass is the core to understanding stoichiometry. Students need to accept the law in practice and note limitations within the lab (“lost” mass in the form of gas, or uncertainty in mass measuring equipment). The Mole 3: What is a Mole? 4: Grams vs. Moles 5: What is Molarity? 100 minutes Students read about the mole and answer some simple molar mass questions including calculating molar mass. Students will measure out a mole of various materials (pop cans for Al, paper clips for Fe), then they are asked how many moles differing amounts of those materials are. For example, 2 pop cans is roughly equal to 1 mole of Al, so students are asked how many moles a single pop can is. Students now read about molarity and learn how moles are factored into determining the concentration of a solution. The will determine the number of moles present in different volumes of the same concentration solution and determine how much volume of different concentration solutions would be needed to have the same number of moles of each. Students should be able to define the term and explain why it is needed and when it is used. They should be able to identify a mole as macroscopic and contrast it to microscopic atoms and molecules. Students should be able to visualize a mole of different substances and be able to convert between grams and moles. While we measure with grams in the lab, moles are needed so we can relate quantities of different chemicals in a chemical reaction. One gram of a chemical does not contain the same number of particles as one gram of another chemical. Students should also be able to use molarity to find moles in a given volume. The mole concept is introduced here so relative amounts in chemical reactions can be discussed for the remainder of the unit. The second half of this lesson serves as the microscopic to macroscopic bridge that is needed to continue to stoichiometry. Molarity is also introduced here as many chemicals students use are actually aqueous solutions in varying molar concentrations. Molar Relationships 6: Limiting Reagents Dictate Molar Relationships 100 minutes Students will watch a demonstration of a metal (either Zn or Mg) reacting with HCl in 5 set molar ratios. The hydrogen gas produced for each ratio with fill a balloon. They will share out their observations about the amount of gas produced in each ratio and if there appears to be any excess unreacted metal remaining in the bottom of the flask. Next students interact with a simulation of the experiment. The first part here focuses on understanding all the components of the simulation, how the simulation works, and some of its limitations. Then students are asked to recreate the demonstration they just watched so they can get quantitative data to work with and reflect on. Students should recognize that specific amounts of reactants in a chemical reaction are needed to produce a specific amount of a product or products. The best possible combination of reactants is the one that produces the maximum amount of product with none of the reactants going to waste. Ratios of reactants matter. Simply adding more of one doesn’t necessarily produce more product. Observing that the ideal ratio does not leave any excess reactant(s) leads to using this ratio as the reason to balance equations in the next lesson. The ideal ratio will reflect balancing the equation for the demonstration reaction. Balancing Equations 7: Reflection on Reaction Simulation and Intro to Balancing/Balancing Simulation 8: Balancing with Molecular Models/Balancing Notes 100 minutes Students will reflect on the demonstration and the corresponding simulation to determine the ideal ratio of metal to HCl. They will use this ratio to balance the equation. They will be guided through an atom inventory of the reaction equation unbalanced and then balanced. Students will balance some basic equations using a PhET simulation. After they are comfortable with basic balancing they will continue with the simulation in game mode. Students will use molecular model kits to balance equations. They will begin by building reactants then disassembling them to build the products. If students have any atoms of the reactants left, they must go back and adjust the number of reactant molecules in such a way that none of the atoms are left over after they build the products. They should draw corresponding models as they use the molecular model kits. After students understand balancing they will be provided with basic notes on a preferred element order to balance equations. Students will learn the term coefficient and how to use an atom inventory to determine if a chemical equation is balanced or not. Students will be able to balance both simple and more complicated equations (such as combustion reactions). This lesson is a continuation of the reaction demonstration lesson. Tying the ideal ratio to coefficients used to balance is important as students realize that balanced equations don’t waste anything. The bulk of this lesson is balancing practice. Students are asked to balance equations in a myriad of ways. If they were not successful with the balancing simulation, then using the molecular model kits and drawing their own models may help them.

## Lessons Overview

1. Lesson 1: Phenomenon Introduction Overview

Students are introduced to the phenomenon. First they will view a SodaStream advertisement, then they will be asked to brainstorm what a makes a fizzy drink fizzy. The phenomenon introduction closes with a teacher demonstration where a carbonated beverage is produced before their eyes without the aid of a SodaStream.

2. Lesson 2: What Happens to Mass During a Chemical Reaction? Overview

Students will perform two different experiments where they are asked to record the overall mass of the reactants and products before and after the reactions takes place. Both experiments will be "closed system" experiments where any gases produced will be trapped by either parafilm or a balloon. Students should observe that overall mass should remain the same before and after each experiment leading them to the law of conservation of mass. This proves that a carbonated beverage can be produced via a chemical reaction.

3. Lesson 3: What is a Mole? Overview

The mole concept is introduced here as a reading so relative amounts in chemical reactions can be discussed for the remainder of the unit.

4. Lesson 4: Grams vs. Moles Overview

In this lesson students will review all quantitative measurement units used in chemistry they have learned thus far in order to compare and contrast microscopic units and macroscopic units. They should come to the conclusion that both moles and grams are macroscopic units while atoms and molecules are microscopic units. They will end by converting between macroscopic units of grams and moles.

5. Lesson 5: What is Molarity? Overview

Molarity is introduced here in a reading as many chemicals students use are actually aqueous solutions in varying molar concentrations.

6. Lesson 6: Limiting Reagents Dictate Molar Relationships Overview

In this lesson, students will observe a double displacement reaction where varying amounts of each reactant are used. They will be asked to focus on the amount of one product in the reaction and how the amount of that product changes relative to the amounts of each reactant used. The goal of the lesson is for students to understand the molar relationships in a reaction and why adding coefficients to a reaction is sometimes necessary.

7. Lesson 7: Introduction to Balancing Chemical Equations Overview

This lesson is a continuation of Lesson 6: Limiting Reactants Dictate Molar Relationships. It connects the ideal ratio that left no excess reactants to coefficients used to balance and equations. Students need to realize that balanced equations don’t "waste" anything. Students will learn the term coefficient and how to use an atom inventory to determine if a chemical equation is balanced or not. Then they will use the balancing simulation. They will complete the introduction first before moving on to the game portion.

8. Lesson 8: Balancing Equations Continued Overview

This lesson is an activity using molecular model kits to balance chemical reactions. Students will build reactants, then disassemble the reactants to build products. Students are also asked to draw models of the overall balanced reactions on their handouts. After students understand balancing they will be provided with basic notes on a preferred element order to balance equations.

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## Standards

Next Generation Science Standards
• Physical Science
• NGSS Crosscutting Concept
• Energy
• NGSS Practice
• Using Mathematics

Computational Thinking in STEM
• Modeling and Simulation Practices
• Assessing Computational Models
• Using Computational Models to Understand a Concept
• Systems Thinking Practices
• Defining Systems and Managing Complexity
• Thinking in Levels
• Understanding the Relationships within a System
• Data Practices
• Analyzing Data

# Lesson 6: Limiting Reagents Dictate Molar Relationships

In this lesson, you will be asked to focus on the amount of one product in a reaction and how the amount of that product changes relative to the amounts of each reactant used. The goal of the lesson is to understand the best possible combination of reactants to use in a reaction so none of the reactants go to waste.