This worksheet asks students to do basic conversions of mass or molecules to moles and *vice versa.* The worksheet requires students to complete their work in a particular format and to inlcude number, unit, and chemical identity for each item in the "given," in each conversion factor, and in the answer. It gives students basic practice in this mathematical exercise while inforcing good habits that encourage "unit analysis" (or dimensional analysis). See below for a link to how this worksheet is used within an entire unit on the basic mathematics for introductory chemistry and stoichiometry. Answers are part of the student document. The teacher document contains blank format pages that may be used for additional practice.

This activity may also be used as a homework assignment.

This worksheet is used early in the course when teaching conversions of various units to and from moles. 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 at http://www.jce.divched.org/article/stoichiometry-easy

If you are logged in to your ChemEd X account, you will see the worksheet available for download in the supporting information.

Unit analysis (dimensional analysis), mole conversions

This worksheet can be used as an in-class or as a homework assignment. The ten items on the first page should take 20 to 30 minutes. The ten items on the second page should take 30 to 50 minutes.

Photocopy of worksheet.

Teachers will recognize the utility of "unit analysis" or "dimensional analysis" when students must carry out unit conversions. This worksheet enforces the good habits of requiring students to list numeral, unit, and chemical identity for each item in a mathematical problem. By determining which units and identities "cancel" students should be able to confirm when they have the mathematics correctly set up and thereby guarantee a correct answer (provided they can work a calculator). In reviewing the mathematical calculation, I believe it is always important to point out that when items "cancel" it means that students are dividing one quantity by the identical quantity, and therefore they end up with the mathematical identity: 1. Of course multiplying or dividing by 1 does not change the value in the answer.

Students complete the worksheet.

See worksheet.

Photocopy the worksheet.

Created by David P. Licata, Chemistry & AP Chemistry, Pacifica High School (retired)

## 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.