Mole %, Weight %, Compositions and Projections

Dexter Perkins
University of North Dakota
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Initial Publication Date: August 22, 2007 | Reviewed: October 18, 2012


This is an introductory exercise intended to get students thinking about mole vs weight % and about the power and problems of projections.

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This is appropriate for an undergraduate Petrology or Mineralogy course.

Skills and concepts that students must have mastered

It helps if students already understand how to convert from moles to grams.

How the activity is situated in the course

I use this during the first week of my Petrology class.


Content/concepts goals for this activity

I use this during the first week of my Petrology class. It is sort of a check -- to make sure students understand how to convert form moles to weight %. Also, I use this to get them thinking about projections -- why we use them and what the limits are, etc.

Higher order thinking skills goals for this activity

Most of this is straightforward. However, students are asked when wt% might be better to use than mole%, and are also asked to speculate on a few things before they do calculations and plotting. So, they are pushed a bit toward higher order thinking skills.

Other skills goals for this activity

Description of the activity/assignment

This activity is a stand-alone problem set that involves converting mineral formulas to mole and weight %. The results are plotted on diagrams, some of which require projections. Students are asked to consider when they would use such diagrams, and also the shortcomings of projections.

Determining whether students have met the goals

We wrap up/evaluate this exercise by having a class discussion. I do not grade it.

More information about assessment tools and techniques.

Teaching materials and tips

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