This worksheet is intended to be used as a "Guided Instructional Activity" (GIA). It asks students to find the molar mass of selected elements and write the molar mass as two equivalent fractions ("conversion factors") and as an equality. In each representation, students are forced to give the numeral of the measure, unit, and identity of the chemical. It is designed to help develop good habits in representing molar mass and other conversion factors, and to emphasize the idea that a conversion factor has a numerator and denominator that "name" identical quantities using different measures.

This activity may also be used as a homework assignment.

This worksheet is used early in the course, as soon as the molar mass concept is introduced. But it is an essential component of lessons leading to stoichiometry. You can access the complete lesson plans with information on their use, and links to other worksheets, labs, and activities.

Log in to your ChemEd X account to download the worksheet from the Supporting Information.

Writing conversion factors.

About 45 minutes.

Each group of two students needs one worksheet.

The proper use of conversion factors makes the common processes of changing mass, number of particles, or volume to moles. Students who learn "dimensional analysis," (or unit analysis) the method of clearly and correctly identifying each measure or constant they wish to use with numeral, unit, and chemical identity, are much more successful in performing these basic math problems. They quickly understand that by being specific with each measure or constant they can determine for themselves, without relying on some chart or mnemonic device, when they have a unit conversion problem set up to give the correct answer.

**Using Guided Instructional Activities**

Guided Instructional Activities (GIAs) were part of the “Mastering Chemistry on the Web” (MCWeb) program, a part of the National Science Foundation Molecular Science Project (http://www.molsci.ucla.edu). Dr. Patrick Wegner (California State University, Fullerton) developed these POGIL-like (Process-Orineted Guided-Inquiry Learning) activities for use in preparatory and general chemistry classes. While some of the activities are, like POGIL real guided inquiry, many are simply cooperative learning activities that give students an opportunity to work toward a common goal while discussing and practicing skills of particular interest.

The usual procedure is to assign students randomly into groups of two (which change for each activity). They work at tables of two groups each. Students who have difficulty with an item are to consult their partner, then the other group at their table, and then may ask the teacher. Students should not move from group to group. The teacher circulates around the class making sure each group is on task, answering questions, and revealing the answers a little at a time so students can confirm they are correctly doing what they were asked to do. This put students in charge of their own learning, gave some the opportunity to “teach” others, and allows the teacher more time to work with students who needed extra attention during class time in a non-threatening environment. At the same time, students police each other to make certain everyone (OK, nearly everyone) is on task.

See the worksheet.

Photocopy worksheets and prepare random groups of students.

Created by David P Licata

## NGSS

Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

*More information about all DCI for HS-PS1 can be found at https://www.nextgenscience.org/dci-arrangement/hs-ps1-matter-and-its-interactions and further resources at https://www.nextgenscience.org.

Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Assessment does not include complex chemical reactions.

Emphasis is on using mathematical ideas to communicate the proportional relationships between masses of atoms in the reactants and the products, and the translation of these relationships to the macroscopic scale using the mole as the conversion from the atomic to the macroscopic scale. Emphasis is on assessing students’ use of mathematical thinking and not on memorization and rote application of problem - solving techniques.