We're going to be honest: we do Physics. That's why this is called The Physics Classroom website. And when we do the Teacher's Notes section for our Concept Builders, we typically have a lot to say ... and a lot of resources to point you to. We're not claiming to be ignorant of chemistry; we just don't have a lot of chemistry resources here at The Physics Classroom to point you to. And so this page is going to be a lot shorter than our usual page that accompanies our Physics Concept Builders. That's our honest confession.

One of the most commonly required skills in a Chemistry course is the skill of determining the molar mass of a compound if given its formula. This Concept Builder addresses that skill. A prerequisite to calculating the molar mass is being able to count the number of atoms of each element in the formula. The first activity of this Concept Builder - Counting Atoms - addresses this pre-requisite skill. The second activity of this Concept Builder - Calculating Molar Mass - focuses on the task of calculating the molar mass of a compound if given its formula. A table structure is used to provide students with an organized approach. The use of the table is a means of requiring the showing of the work as students must count the number of atoms of each element and use the atomic mass to calculate the mass of those atoms (assuming one mole of the compount). Finally students must add up all these masses to determine the molar mass. Checking answers is easy and can be done an unlimited number of times without penalty. Each time answers are checked, a color-coding system is used to provide feedback. Correct answers are color-coded green and cannot be subsequently changes. Incorrect answers can be deleted and recalculated. 

The third activity - Out of This World - is just that. While online calculators can be easily used to complete the second activity, the third activity can only be completed if you know what you're doing. The elements are the fictional elements from the planet Maydeup. A separate Periodic Table is provided and can be used to determine the molar mass of these compounds. The same table structures using in the seond activity is used in the third activity. 

Each Question Group ini this Concept Builder contains three nearly identical questions. The specific question a student receives is selected at random. The ordering of questions is also randomized and the order in which questions are delivered to students is also randomized. The result is every students' experience is different enough that two side-by-side students will have to do more than copy answers to be successful. 

We recommend that students use at least three significant digits in their answers. The answer checking algorithm makes sure that the student inputted answer is within 1% of the keyed answer (known to 16 digits). Using three significant digits on answers may be a deparature from the rules of significant digits but it avoids errors owed to rounding. 

Teachers using the Concept Builder with their classes should preview the activity (or view the Questions on a separate page) in order to judge which difficulty levels would be most appropriate for their students.

 

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.