Visualizing Stoichiometry Solutions

 

Rebecca Pittman, Educator, Mathematics & Science Center

 

Developed with funding from the Mathematics & Science Center

 

Major

Understanding

Stoichiometry is a branch of chemistry that deals with the quantitative relationship between two or more substances in a chemical reaction.

 

Grade/Subject

Chemistry

 

Objectives

 

 

 

Given a balanced chemical equation, periodic table of the elements, calculator and stoichiometry flow chart, solve word problems that deal with the relative quantities of reactants and products involved in a chemical reaction.

 

Create graphic organizers to support mastery of other chemistry concepts.

 

 

Time

Introduction/Pre-Assessment

5 min

 

 

Activity 1 and 2

20 min

 

 

Discussion of results

5 min

 

 

Activity 3:  Individual Challenge

20 min

 

 

Discussion of results

10 min

 

 

Limiting Reagent Challenge

10 min

 

 

Online Practice

variable

 

 

Closure 

5 min

 

 

Materials

For each student:

1 copy of Stoichiometry Solutions Flowchart

1 copy of Stoichiometry Calculations Worksheet

Periodic Table of the Elements (http://www.webelements.com)

Calculator

Computer with Internet access (optional)

 

For the teacher:

1 computer projection system or overhead projector

PowerPoint presentation

 

State and National

Correlations

Virginia Standards of Learning: Chemistry (CH.4); Technology (C/T 9-12.8)

National Science Education Standards: Chemical reactions; Student development of abilities and understanding.

 

 

Instructional

Strategies

Introduction/Pre-Assessment:  PowerPoint slides 2,3

Define stoichiometry.

Pose the question:  “What do you already know about chemical equations?”  Elicit responses from students.  Lead the discussion to include what happens during a chemical reaction; what information a chemical equation gives us; what is a balanced chemical equation and what scientific law a balanced chemical equation demonstrates.

Define ‘mole’ in terms of a number of particles and a unit of mass.




 

Activity 1:  Using a Flow Chart – PowerPoint slides 4,5,6,7

Trace the steps on the student flowchart as the first equation table is created and the problem solved.

 

 

Activity 2:  Group Practice

Assign Exercise 2 as a group activity with students working in pairs to set up an equation table and solve the problem. 

 

 

Discussion of results

Ask one group to explain their results at the board.

Optional: PowerPoint slides 8 and 9 may be used for teacher discussion of the results.

 

 

Activity 3:  Individual Challenge

Introduce Exercise 3.  Ask students to complete this exercise as teacher moves around the room to monitor progress and answer questions.

 

 

Discussion of results

Teacher led discussion using PowerPoint slide 10.  Elicit answers from students before disclosing the strategy and final results.

 

 

Limiting Reagent Challenge

Use the following scenarios to define limiting reagent. Present the class with a closed jar containing a piece of charcoal and the following questions.

 

1.  If the charcoal is lit and the lid quickly screwed back on the jar, will all the oxygen in the jar be consumed as the charcoal burns?

2.  If the charcoal is lit and the lid left off the jar, will all of the oxygen in the room be used up as the charcoal burns to completion?

 

Define term:   A limiting reagent is any reactant that is used up first in a chemical reaction.  When the limiting reagent has been consumed the reaction stops.  A limiting reagent thus determines the amount of product that can be formed in the reaction.

 

What was the limiting reagent in the scenario when I put the lid on the jar containing the lit charcoal?  Explain.

 

What was the limiting reagent in the scenario when I left the lid off the jar containing the lit charcoal?  Explain.

 

Present students with the limiting reagent problem on PowerPoint slide 11.  Explain that the equation flow chart may be used to solve for each reactant separately.  Ask students how the results of the calculations can be used to identify the limiting reagent.  (The reactant that produces the least amount of product is the limiting reagent.)

 

Use slide 12 to discuss the results.

 

 

Practice

Online Practice

Use “Electronic Flashcard” at http://garnet.acns.fsu.edu/~rlight/stoich/

to generate additional practice problems.  

 

 

Closure

Ask students to discuss other applications where flow charts could be used to support learning in chemistry class or across the curriculum.

 

Extensions

Explore other graphic organizer models at http://www.glencoe.com/sec/teachingtoday/weeklytips.phtml/31.  Choose 2 or 3 models that may be used as study strategies for chemistry class.

 

Assessment

Sample items are provided for use in checking students’ understanding.

Paper Pencil Test

Paper Pencil Test Key
Performance Product Rubric

 

The following table shows how the assessment items are related to specific objectives.

 

Objective

Paper-Pencil

Test

Product/

Performance

Given a balanced chemical equation, periodic table of the elements, calculator and stoichiometry flow chart, solve word problems that deal with the relative quantities of reactants and products involved in a chemical reaction.

1,2

 

Use a graphic organizer to support mastery of chemistry concepts.

 

3,4

 

Teaching Tips

 

Use the pen option within PowerPoint to trace each step on the flowchart on the projected image during the introduction to the chart.  This will familiarize students with use of the flowchart as well as introduce them to construction of an equation table.  In lieu of the PowerPoint presentation one may use a transparency of the Stoichiometry Solutions flowchart and overhead pen to trace the steps on the flowchart as the problem is completed on a classroom board.

 

References

Electronic Flashcard

This online applet provides practice and feedback for stoichiometry solutions.

http://garnet.acns.fsu.edu/~rlight/stoich/

 

The ChemCollective:  Stoichiometry Simulations and Virtual Lab Problems    

The Chemistry Collective is a collection of virtual labs, scenario-based learning activities, and concepts tests which can be incorporated into a variety of teaching approaches as pre-labs, alternatives to textbook homework, and in-class activities for individuals or teams.

http://www.chemcollective.org/

 

CHEMTUTOR

CHEMTUTOR offers an alternative approach to solving stoichiometry problems called the “Roadmap”.

http://www.chemtutor.com/mols.htm#road

 

Mathematics & Science Center
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http://mathsciencecenter.info

 

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