### Notes:

The Particles .. Moles .. Mass Concept Builder is an adjustable-size file that displays nicely on smart phones, on tablets such as the iPad, on Chromebooks, and on laptops and desktops. The size of the Concept Builder can be scaled to fit the device that it is displayed on. The compatibility with smart phones, iPads, other tablets, and Chromebooks make it a perfect tool for use in a 1:1 classroom.

### Teaching Ideas and Suggestions:

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.

A typical objective in most chemistry courses is to be able to use the concept of the mole as a counting unit to relate the mass of a sample of some substance to the number of particles of that substance. For most teachers, the relating process centers around the use of conversion factors and the factor label method. This Concept Builder was designed to provide opportunities for students to internalize the relationship between these three quantities - particles, moles, and mass - through the use of conversion factors or by use of a ratio. The activity consists of three scaffolded difficulty levels, each of which involves the completion of a table. The table contains column headings like Formula, # of Particles, # of Moles, Mass (in Grams). The table has several incompleted cells and students must use their understanding of the topic to complete the table cells.

Each difficulty level has four different tables. The tables are randomly selected such that different students will have different tables. The Apprentice Difficulty Level, the molar mass values are given and the provided numbers in the cell are "nice". By saying they are "nice", we mean they are easily divisible by the molar mass or by Avogadro's number to yield a whole or a half number. Many students with a strong math comfort will be able to perform all math operations without a calculator. In the Master Difficulty Level, an additional variable is added - the molar mass. The molar mass must be calculated from the given formula. The formulae ini the Master Difficulty Level is more sophisticated than that of the Apprentice Difficulty Level; there is typically a polyatomic ion in the formula. And some but not all of the given numbers in the table are nice numbers.  The Wizard Difficulty Level involves all the same math operations as the Master Difficulty Level, but none of the numbers are nice numbers and the formulae for the substances include parenthesis and thus slightly more difficult molar mass calculations.

This Concept Builder includes a Hint feature. Students can access a hint about how to convert between the number of particles and the number of moles and between the number of moles and the mass in grams. These hints can be accessed by tapping on the CF buttons that are located between the columns of data. Tapping on the button will slide in a Hint with an example conversion. When done viewing the hint, students can tap on the Done button and return to the table. Students can use these buttons as often as they like. But in the Master and Wizard Difficulty Level, a tap on the buttons results in an adjustment to the Health Rating (described below).

We recommend that students use 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 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 Health Rating:

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.

### Getting Help:

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.