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Limiting Reactants: Industrial Case Study

Authored by Dave Blackburn, Century College, White Bear Lake MN
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This material is replicated on a number of sites as part of the SERC Pedagogic Service Project

Summary

Students are assigned as "consultants" to evaluate competing manufacturing processes based on reactant ratios, percent yield, and refining/waste disposal costs. Three competing models are proposed. Directions are open-ended.

Learning Goals

Students should integrate concepts of percent yield with given data, and choose criteria for recommending one method or another.

Context for Use

Activity should take 15 to 30 minutes depending on student ability level and instructor guidance. Activity can be used after limiting reactants/percent yield concepts introduced, thus early to middle of first semester general chemistry.

Description and Teaching Materials

Uploaded file is a MS Word document with my comments on it after the first classroom use. Edit as needed and please send feedback.
The students evaluate mass ratios for making NiO from nickel nitrate and NaOH. Postulated costs for raw materials are given. Three mass ratios are suggested, with different percent yields and different costs for refining the crude product to salable nickel oxide. Students are asked to choose the best of the three given ratios and explain what criteria they used for their choice; and to come up with the "ideal" ratio from stoichiometric concepts.
Assignment handout with instructor comments (Microsoft Word 64kB Oct27 08)

Teaching Notes and Tips

Students may notice there are two ways of balancing the synthesis, with a 1:1 or a 2:1 ratio of reactants. The 1:1 ratio gives HNO3 as a byproduct - if a group suggests this route, ask about if the HNO3 might interfere with the NaOH reactant.

Assessment

The main assessment of this comes from students' reports of how & why they made their choice. The reports can be done orally, if time; as written homework; or on line.
Students will get stuck if they can't figure out the mass ratios and significance of percent yield. The instructor's observations and coaching during the exercise are the key feedback mechanism.

References and Resources

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