Notes

Stoichiometric conversions and analysis are likely the most pervasive topic in an introductory chemistry course. Whether a basic high school course or a more math-heavy honors course, you can bet that at some point the idea of a mole-to-mole conversion will be discussed. And for the more math-heavy course, gram-to-gram conversions are a sure bet. This Concept Builder targets the task of converting from the given mass of a reactant to the mass of product (or a comparable gram-to-gram conversion).

The Mass Stoichiometry Concept Builder is comprised of 18 questions spread across three different difficulty levels. Each question organizes information in a table where each column of the table represents a species in a given chemical equation. For each row of the table, students are provided the mass of a reactant or a product and must calculate the corresponding mass of reactant(s) reacted and/or product(s) produced. Each question involves either 10 or 12 gram-to-gram stoichiometry calculations, depending on the difficulty level. The Apprentice Difficulty Level includes a synthesis reaction (two reactants and one product) and 10 calculations. The provided numbers are "nice"; they are typically a whole number multiple of the molar mass. The Master Difficulty Level includes a hydrocarbon combustion reaction (two reactants and two products) and 12 calculations. The provided numbers are "nice". The Wizard Difficulty Level also includes a hydrocarbon combustion reaction and 12 calculations. The provided numbers are "nasty". Students can use the Check Answers button at any time to check the accuracy of their calculations. Feedback is immediate and students can correct their mistakes. The exact questions are shown below.

We view this Concept Builder as being most valuable in the early stages of teaching and learning about gram-to-gram conversions. The levels begin with simple numbers that are simple whole-number (usually) multiples of the molar mass values. As a student progresses from level to level, the reaction becomes more involved (two products, larger coefficients) and the given numbers have nor clear mathematical relationship to the molar mass values. An added bonus of the table format is that after the mass of all reactants and all products are calculated, students can see that mass is conserved.

Student answers are considered correct if they fall within 2% of the keyed answer. We recommend that students use at least 3 significant figures for their molar mass values and enter their answers to at least three significant digits. Feedback is provided after each submission. If a student's answer is correct, the answer field turns green. If it is not correct, then the answer field turns pink. Answers can be entered directly into the field from a device keyboard. Those who are using mobile devices or touch screens may prefer our built-in number pad. A tap on the number pad icon next to a field will pop up a built-in number pad that does not cover any part of the question.

This Concept Builder was intended as an in-class activity. 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 activities would be most appropriate for their students. View Questions (for Task Tracker Teachers Only).

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.