Density and Buoyancy with Centrifugation (a 3 pp activity with technical application)

Interactive, scaffolded model

Overview and Learning Objectives

Because density is a property of a substance, regardless of the amount of that substance, it can be used to separate one material from another. This activity can be used to explore the relationship between atomic mass, volume, and density, and to relate these to the technique of centrifugation.

Students will be able to:

• explain why some things float and others do not;
• connect the results of centrifugation with density;
• analyze the impact of temperature on centrifugation.

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Assessment

Download the pre/post assessment from:

http://www.concord.org/~barbara/workbench_web/pdf/density_ASSESS.8.07.pdf

rubric

http://www.concord.org/~barbara/workbench_web/pdf/density.RUBRIC.8.07.pdf

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Classroom Practice

(Submitted by Molit project teacher) Density is a topic commonly covered at the beginning of the semester in a first semester general chemistry course. This topic is usually taught as a numerical problem, e.g., density = mass/volume, how to calculate density, how to measure density, etc. The activity will be used as supplementary material to give students a molecular level understanding of density and to broaden their horizon beyond that of numerical problem solving. (Mitsuko Fujiwara - Parkland College)

Mitsuko's procedure:

1. Hand out the instruction sheet and explain what the students are expected to do for this computer lab. Encourage students to ask questions.
2. Hand out the pre-test. Emphasize that they are not expected to know all the answers, so they should provide the answer to the best of their knowledge and that they will be get full credit for any answer on the pre-post test. They will be mildly graded on the activity report.
3. The students will go through the activity at their own pace (one student per computer). Students are allowed to talk to each other, help each other, ask questions, open book, open notes, etc.
4. Collect the activity report printouts from students and make sure they submitted the report electronically to Concord.
5. Hand out the post-test.
6. Read through pre-post tests and grade the activity report of each student.
7. Return graded activity report and discuss questions from the report.

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Central Concepts

Key Concept:

Because density is a property of a substance, regardless of the amount of that substance, it can be used to separate one material from another.

Additional Related Concepts

Physics/Chemistry

• Buoyancy
• Density
• Mass

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Activity Credits

Created by CC: Molecular Literacy using Molecular Workbench

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Requirements

• Java 1.5+ - Java 1.5+ is available for Windows, Linux, and Mac OS X 10.4 and greater. If you are using Mac OS X 10.3, you can download MW Version 1.3 and explore within it instead.

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