Summary

In this lesson, students will identify limiting reagents (and the amounts of product produced) using the mole of reaction concept. This approach is designed to focus on calculations related to limiting reactant after a conceptual understanding of what a limiting reactant is has already been established.

Grade Level

High School

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• HS-PSI-7: Using mathematical representation to support the claim that atoms, and therefore mass, are conserved during a chemical reaction
• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking

Objectives

By the end of this lesson, students should be able to:

• Use the concept of mole of reaction to identify the limiting reactant of a reaction when starting with either moles or grams of the reactants.
• Use the concept of mole of reaction to calculate the moles or grams of products produced when starting with either moles or grams of the reactants.
• Use the concept of mole of reaction to calculate the moles of excess reactant leftover at the end of a reaction when starting with moles of the reactants (can be extended to include grams of excess reagent if desired).

Chemistry Topics

This lesson supports students’ understanding of:

• Chemical Reactions
• Stoichiometry
• Conservation of Matter
• Limiting reactants

Time

Teacher Preparation: 5-10 minutes

Lesson: Two sessions of approximately 45 minutes each (see teacher notes for additional details)

Part I:

• Warm up (Conceptual limiting reactant review): 5 minutes
• Instruction: Mole of reaction and limiting reagents introduction: 20 minutes
• Group work: Work on provided worksheet #1 in small groups: 15 minutes
• Wrap up: (Exit Ticket): 5 minutes

Part II:

• Warm up (Moles of reaction limiting reactant review): 5 minutes
• Instruction: Mole of reaction and limiting reagents including grams: 20 minutes
• Group work: Work on provided worksheet #2 in small groups: 15 minutes
• Wrap up: (Exit Ticket): 5 minutes

Materials

Part I:

• PowerPoint Slides: Warm-Up and Exit Ticket Questions Part I
• PowerPoint Slides: Basics of Mole of Reaction (slides 1-9 only)
• Practice worksheet (one per student)
  • Worksheet #1: Limiting Reactant and Mole of Reactant (Moles only)
• Calculator
• Periodic Table
• Pencil

Part II:

• PowerPoint Slides: Warm-Up and Exit Ticket Questions Part II
• PowerPoint Slides: Basics of Mole of Reaction (slides 10-15)
• Practice worksheet (one per student)
  • Worksheet #2: Limiting Reactant and Mole of Reactant (Grams)
• Calculator
• Periodic Table
• Pencil

Safety

• No specific safety precautions need to be observed for this lesson.

Teacher Notes

• To learn more about this activity, read the corresponding article, Mole of Reaction: Application in Limiting Reactants, published in the September 2020 issue of Chemistry Solutions.

• General Notes:
• The answer keys for warm-up and exit ticket questions are located in the slide notes (below each slide).
• Answer keys for the worksheets are provided as separate documents.
• Prior to this activity, students should have been exposed to the concept of limiting reactants, but not how to do molar or gram calculations. For example, the author has used the PhET “Reactants, Products and Leftovers” simulation (including the game feature) prior to this lesson.

Part I

• Warm Up Question (Conceptual Limiting Reactant)
  • Students will begin the lesson by individually working the provided problem. This problem can be shown on a projection screen or white board (slide of problem with answers included), given as a hard copy, or written on the board.
  • The goal of this warm-up problem is to activate the students’ prior conceptual knowledge of limiting reactants.
  • After individual work, students can discuss their answers with a neighbor to check their understanding.
  • (Optional) The teacher can collect the warm-up problems as a check of understanding or can ask for volunteers to share their answers. The entire warm-up, however, is intended to take no longer than 5 or so minutes.
• Instruction: Basics of Mole of Reaction
  • This discussion uses slides #1-9 of the provided slide presentation.
  • The presentation includes animations so the teacher can use it to scaffold a discussion. In addition, the animations allow the teacher to present the information is stages (as opposed to all at once).
  • The teacher can use the provided presentation to lead a discussion introducing the concept of mole of reaction and how it can be used to identify limiting reagents, predict moles of products and predict moles of excess reagent remaining. The goal is to get students comfortable with the concept of mole of reaction before they do full stoichiometric calculations. If desired, teachers can substitute their own approach to these topics, but the goal here is to work on student ability to relate mole of reaction to reaction coefficients and the concept of limiting reactants.
  • The lesson is designed for the teacher to first introduce the concept of mole of reaction, second do an example for student (slides #1-4), and last provide an example for students to work on independently (slide #5). After giving students time to work on this example (time will vary based on student level), the teacher can walk students through the solution (slides #6-9).
• Group Work: Worksheet #1
  • It allows the students to practice using moles of reaction to identify limiting reactants, moles of products produced, and moles of excess reagent remaining.
  • As written, students should have time to start the worksheet in class in small groups (2-4 students). Depending on their speed, they may need to complete the worksheet for homework. The worksheet is expected to take about 15 minutes to complete.
  • While the students are working on the activity, the teacher can circulate and provide individual support (as needed).
  • The end of this group work is a good break point with the exit ticket (details below) serving as a concluding activity.
• Exit Ticket #1 (Conceptual Limiting Reactant)
  • Students will end the lesson by individually working the provided problem.
  • This problem can be shown on a projection screen or white board (Slide of problem with answers included in slide notes included), given as a hard copy, or written on the board.
  • While the students are working on the activity, the teacher can circulate and provide individual support (as needed).
  • The goal of this exit ticket is for the teacher to have a sense of how well students have internalized the mole of reaction concept as it relates to limiting reagents.
  • (Optional) The teacher can collect the exit ticket as a check of understanding.

Part II

• Warm Up Question (Calculating Limiting Reactant using mole conversions only)
  • Students will begin the lesson by individually working the provided problem which reviews the focus of part I. This problem can be shown on a projection screen, white board (Slide of problem with answers included in slide notes included), or given as a hard copy or written on the board.
  • The goal of this warm-up problem is to activate the students’ understanding of part I.
  • After individual work, students can discuss their answers with a neighbor to check their understanding.
  • (Optional) The teacher can collect the warm-up problems as a check of understanding or can ask for volunteers to share their answers. The entire warm-up, however, is intended to take no longer than 5 or so minutes.
• Instruction: Extending mole of reaction Limiting Reactant calculations to grams
  • This discussion uses slides #10-15 of the provided Slide presentation
  • The Slide presentation includes animations so the teacher can use it to scaffold a discussion. In addition, the animations allow the teacher present the information is stages (as opposed to all at once).
  • The teacher can use the provided Slide presentation to lead a discussion extending the concept of mole of reaction and how it can be used to identify limiting reagents to predicting the product grams that can be generated. The goal is to get students comfortable using the concept of mole of reaction with full stoichiometric calculations.
  • The lesson is designed for the teacher to first work an example for student (slides #10-12) then provide an example for students to work on independently (slide #13). After giving students time to work on this example (time will vary based on student level), the teacher can walk students through the solution (slides #14-15).
  • Optional: If desired teachers can add to this by including examples where students calculate the grams of excess reactant remaining. This was omitted to focus the students’ attention on the most common type of LR problem, but could be included if teachers felt it was appropriate for their students.
• Group work: Worksheet #2
  • It allows the students to practice using moles of reaction to identify limiting reactants and product grams produced.
  • As written, students should have time to start the worksheet in class in small groups (2-4 students). Depending on their speed, they may need to complete the worksheet for homework. The worksheet is expected to take about 15 minutes to complete.
  • While the students are working on the activity, the teacher can circulate and provide individual support (as needed).
• Exit Ticket #2: Limiting Reactant with grams calculations
  • Students will end this part of the lesson by individually working the provided problem. This problem can be shown on a projection screen or white board (Slide of problem with answers included in slide notes included) or given as a hard copy or written on the board.
  • While the students are working on the activity, the teacher can circulate and provide individual support (as needed).
  • The goal of this exit ticket is for the teacher to have a sense of student skill in solving full stoichiometric limiting reactant calculations using the mole of reaction concept.
  • (Optional) The teacher can collect the exit ticket as a check of understanding.