Stoichiometry is a central part of every Chemistry course. An understanding of the relationship between the amounts of reactants and products involved in a reaction is central to chemistry. For many teachers, this part of the course involves a heavy reliance upon the use of the factor label method. Stoichiometry - the quantitative study of the amounts of reactants and products - becomes a collection of
conversion factor exercises. And when properly implemented, students become good at performing 3-step (and longer) conversions in which they determine the mass of product produced from a given amount of reactant. But being able to cancel units and solve a conversion factor problem does not insure that there is any understanding of the relationship between the amounts of reactants and products involved in the reaction. Solving a problem via a well-taught, well-practiced algorithm is not equivalent to undrstanding stoichiometry. This Concept Builder addresses this issue. It does not include "conversion factor problems". This Concept Builder focuses on relationships. Students who understand the relationships between the amounts of reactants and products - whether expressed in grams or in moles - will likely breeze through the exercise. Those who do not will be repeating the refrain
What am I supposed to do?
This Concept Builder can be used at any time during a unit on Stoichiometry. In fact, it might be interesting to use it early as students are developing an understanding of the meaning of the coefficients and the role of molar mass in relating the moles to the grams of any substance ... and also nearer the end of the unit after there's been a steady barrage of complext conversion factor problems. There are three difficulty levels in the Concept Builder -
Apprentice,
Master, and
Wizard. Each difficulty level includes a table of numerical data which must be accurately completed. Success involves accurately filling in the missing cells of the table. The learner can check a calculation as many times as needed. But every miss is counted and a Health Report is displayed once the table has been completed. The formula for determining a Health Rating is shown
on a separate page. Students can repeat the exercise as many times as needed to improve their grade above a minimum-required level.
The
Apprentice Difficulty Level centers around the completion of a 5-row table of numerical data with (mostly) three empty cells per row. Each row can be thought of as a separate problem. The provided chemical equation includes two reactants and two products. To complete the table, students must be able to use the coefficients in the balanced chemical equation.
The
Master Difficulty Level is slightly more difficult than the
Aprrentice level. It also centers around the completion of a 5-row table with (mostly) three empty cells per row. The balanced chemical equation includes two reactants and one product. There is a fourth column in the table where the mass of the product must be calculated from the number of moles of product.
The
Wizard Difficulty Level centers around the completion of a 5-row table with (mostly) three empty cells per row. The reaction involves two reactants and one product. Two of the four columns in the table include the amounts of one of the reactants and the one product and the mass of each.
This Concept Builder was intended as an in-class activity. After some lab work, some discussion of how to relate the amounts of reactants and products, and some guided practice, allow students to try it for themselves. Teachers using the Concept Builder with their classes should preview the activity (or view the
Questions in a separate file) in order to judge which levels would be most appropriate for their students.
Students can complete as much of the table as they wish before checking their answers. And they can check their answers as many times as they wish. Feedback regarding the correctness of their answers is immediate and provided using a color-coding system. Correct answers are displayed in a table cell with a green background; these correct answers become
locked and cannot be changed. Incorrect answers are displayed in a table cell with a red background. Each time students check their answers, the number of missed answers is determined. A running tally is kept of the number of misses. When a student accurately completes the table, a Health rating is displayed on the screen. The Health rating is dependent upon the number of misses. Formulas for computing the Health rating are discussed
on a separate page. The Health rating is also displayed on the Main Menu screen for any completed difficulty level. A student can always repeat a difficulty level in order to improve their Health rating for that level. The best Health rating is always displayed on the Main Menu screen below the trophy for that difficulty level.
We leave it to the discretion of individual teachers as to what they wish to do with the Health rating information. We recognize that there will be some teachers who feel most comfortable with their students in simply requiring that a difficulty level be completed and trophy be earned. Other teachers may wish to require completion of a difficulty level with a minimum Health rating. For instance, such teachers may require that each difficulty level be completed with a 70% or higher Health rating. Still other teachers may tie the Health rating into a grade or allow a homework pass for completing an activity that exceeds a 90% Health rating. Decisions as to what to do with the Health rating are best left for individual teachers who know their students the best.
The most valuable (and most overlooked) aspect of this Concept Builder is the Help Me! feature. Each question group is accompanied by a Help page that discusses the specifics of the question. This Help feature transforms the activity from a question-answering activity into a concept-building activity. The student who takes the time to use the Help pages can be transformed from a guesser to a learner and from an unsure student to a confident student. The "meat and potatoes" of the Help pages are in the sections titled "How to Think About This Situation:" Students need to be encouraged by teachers to use the Help Me! button and to read this section of the page. A student that takes time to reflect upon how they are answering the question and how an expert would think about the situation can transform their naivete into expertise.