How Sweet Is Your Tea? -- Practical experience with solutions and concentration

This material is replicated on a number of sites as part of the SERC Pedagogic Service Project

Summary

This Spreadsheets Across the Curriculum activity is an exercise to introduce the concept of concentration as a ratio as well as the idea of using Excel spreadsheets to solve quantitative problems. Students calculate, first with a calculator, then with an Excel spreadsheet, the amount of solute and solvent required to prepare several simple solutions. They learn to estimate if their calculations are resaonable. At the end of the module, students will have developed an Excel template that will facilitate the calculations for any simple solution.

Learning Goals

Students will:

• Learn to see concentration as a ratio of solute and solvent.
• Design and organize two simple spreadsheets.
• Determine the cell equation to calculate the amount of solute required to prepare a chosen volume of solution at a chosen concentration.

In the process the students will:

• Learn how to do some very basic calculations with Excel.
• Learn how the idea of concentration affects us daily.
• Gain some familiarity with the terms "orders of magnitude" and "scientific notation".
• Learn how Excel can be a powerful tool for carrying out repetitive computations.

Context for Use

This module was developed for use as a prelaboratory tutorial in an introductory (freshman-level) cellular and molecular biology class at Colby-Sawyer College. The laboratory exercise that it complements is the first of four that, together, serve early in the semester to familiarize students with the basic laboratory equipment at their disposal. The exercises also help develop skills and understanding necessary for the laboratory work throughout the semester.

This tutorial focuses on concentration and the preparation of solutions. It introduces basic concepts and vocabulary and shows students how to perform the calculations used to determine the amount of solute required to make a solution of specified concentration and volume.

The module is very basic. It is designed to serve primarily as a refresher for students who have already learned the material but have forgotten aspects of it. However, because the module is so basic, it can be used to teach students who have not encountered the concepts before. As it is the first of several modules that the students encounter duing the semester, it has the added tasks of teaching students to use spreadsheets to solve quantitative problems as well as to process and present data in the laboratory report due at the completion of each exercise.

The tutorial is used every semester. I typically assign the tutorial as homework to be completed by the students on their own and handed in before the laboratory in question. However, on occasion I start the class on the tutorial during the last 15 minutes of the laboratory period preceding that in which they will actually prepare the solutions. I expect the skills and concepts illustrated by the exercise and the tutorial to be applied where approptiate in all subsequent work throughout the semester.

Description and Teaching Materials

SSAC2007.QD31.WT1.2_Stdnt (PowerPoint 586kB Aug12 07)

The module is a PowerPoint presentation with embedded spreadsheets. If the embedded spreadsheets are not visible, save the PowerPoint file to disk and open it from there.

This PowerPoint file is the student version of the module. An instructor version is available by request. The instructor version includes the completed spreadsheet. Send your request to Len Vacher (vacher@usf.edu) by filling out and submitting the Instructor Module Request Form.

Teaching Notes and Tips

This module was designed primarily as a simple, rapid review of basic concepts and vocabulary associated with concentration and the preparation of solutions. The first "wet' lab of the semester requires students to prepare solutions for later use, and over the years I have found that it takes students a very long time to carry out the calculations for even the simplest solutions. This module evolved to help remedy that problem.

The module was developed for another reason, as well. The collective experience of several Colby-Sawyer College science faculty members using such modules in their classes is that students become more at ease with spreadsheet modules and learn more effectively from them with each new module that they encounter. That certainly has been my personal experience. The first module that I developed (Calibrating a Pipettor) was actually written for a later, more involved laboratory exercise. In assigning that module to students as a prelaboratory exercise, I found that students struggled to learn the central concepts of that module at the same time as they were learning to use Excel as a tool. Thus this second module, "How Sweet is Your Tea?' evolved as an introductory module to teach the basic approach of using Excel as a calcuating tool. To be successful in that role, it had to be very simple, conceptually as well as at the level of the Excel skills required. For that reason it can also be used to teach concentration and the preparation of solutions to students encountering the concepts for the first time.

Assessment

Associated with this module is a pre/post test that can be administered before and after the students have gone through the module in order to determine what they have learned from the experience. It is worth considering just when after completion of the module (immediately, a day later, a week later?) students should be retested to best evaluate their learning. For my personal purposes, even more telling evaluation consists of noting how much faster the students can prepare their solutions during the first laboratory period, how much more clearly they explain and discuss what they have done in the report due at the conclusion of the laboratory exercise, and how much more easily they work through and learn from the second, more complicated module that they encounter after this first one than have previous students who did not have exposure to this first module.

References and Resources

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