Making Solid Solutions with Alkali Halides (and Breaking Them)

John B. Brady

Smith College

This activity is part of the On the Cutting Edge Exemplary Teaching Activities collection and has been reviewed by 1 other review process

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This activity was selected for the On the Cutting Edge Exemplary Teaching Collection

Resources in this top level collection a) must have scored Exemplary or Very Good in all five review categories, and must also rate as “Exemplary” in at least three of the five categories. The five categories included in the peer review process are

Scientific Accuracy
Alignment of Learning Goals, Activities, and Assessments
Pedagogic Effectiveness
Robustness (usability and dependability of all components)
Completeness of the ActivitySheet web page

For more information about the peer review process itself, please see http://serc.carleton.edu/NAGTWorkshops/review.html.

This activity was peer reviewed prior to publication in the Teaching Mineralogy Workbook.

This teaching activity was originally published in: Brady, J., Mogk, D. W., and Perkins, D., (editors), 1997, "Teaching Mineralogy," a workbook published by the Mineralogical Society of America, 406 pp. All teaching activities in this volume received two external peer reviews from mineralogy faculty focused on content and pedagogy, and a final review by the co-editors to comply with the publication standards of the Mineralogical Society of America.

This page first made public: May 9, 2008

Summary

In this exercise, the class will grow a variety of crystals of the same mineral, but with different chemical compositions. These crystals will be made from mixtures of halite eNaCI)and sylvite (KCI) that are melted and cooled. The principle goal of these experiments is to demonstrate that solid solutions do occur and that their physical properties vary with their chemical composition. Additional goals include studying the effect of composition on melting, exploring the process of exsolution as a function of temperature, and seeing the effect of fluids and deformation on crystallization kinetics.

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Context

Audience

This activity is designed for an undergraduate required course in mineralogy and is generally for sophomore or junior level students.

Skills and concepts that students must have mastered

Basic mineralogy and crystallography
Interpreting graphs

How the activity is situated in the course

This activity is a stand-alone exercise, but is part of a larger volume of classroom and laboratory activities from "Teaching Mineralogy," a workbook published by the Mineralogical Society of America, Brady, J., Mogk, D. W., and Perkins, D., (editors), 1997,406 pp.

Goals

Content/concepts goals for this activity

This activity aids students' understanding of:

kinetics of crystallization, nucleation and growth, exsolution, and diffusion in the NaCl-KCl system
phase diagrams using the NaCl-KCl system

Higher order thinking skills goals for this activity

This activity should improve students' skills in:

analysis and interpretation of data, especially as it relates to graphical interpretation
comparison of data between different phases in the NaCl-KCl system

Other skills goals for this activity

This activity may also improve students' ability to:

work collaboratively in small groups
understand and operate an XRD

Description of the activity/assignment

In this exercise, the class will grow a variety of crystals of the same mineral, but with different chemical compositions. These crystals will be made from mixtures of halite (NaCl)and sylvite (KCl) that are melted and cooled. Because K⁺¹ is significantly larger than Na⁺¹,the unit cell is larger in sylvite than in halite. Intermediate compositions have intermediate unit cell sizes. Thus, a measurement of the lattice spacing of the crystalline products of your experiments can be used to determine their chemical composition. The principle goal of these experiments is to demonstrate that solid solutions do occur and that their physical properties vary with their chemical composition. Additional goals include studying the effect of composition on melting, exploring the process of exsolution as a function of temperature, and seeing the effect of fluids and deformation on crystallization kinetics.

Determining whether students have met the goals

Students have met the goals of this exercise if they have answered the thought questions completely and accurately thereby demonstrating that they are able to analyze and interpret the data they collect.

More information about assessment tools and techniques.

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Other Materials

Assignment description, hand outs, and instructor's notes. (Microsoft Word 236kB Apr27 08)

Assignment figure 1 (Microsoft Word 190kB Apr27 08)

Assignment figure 2 (Microsoft Word 116kB Apr27 08)

Assignment description, hand outs, and instructor's notes. (Acrobat (PDF) 47kB May3 08)

Supporting references/URLs

Brady, J., Mogk, D. W., and Perkins, D., (editors), 1997, Teaching Mineralogy, a workbook published by the Mineralogical Society of America, 406 pp.

Barrett, W.T., and Wallace, W.E., 1954, Studies of NaCl-KCl solid solutions. 1.Heats of formation, lattice spacings, densities, Schottky defects and mutual solubilities: Journal of the American Chemical Society, 76, 366-369.

Levin, E.M., Robbins, C.R., and McMurdie, H.F., 1964, Phase Diagrams for Ceramists: The American Ceramic Society, Columbus, 60lp.

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