# 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

## 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