# Buffer Capacity in Chemical Equilibrium: How long can you hyperventilate before severe alkalosis sets in?

#### Summary

In this Spreadsheets Across the Curriculum module, students build spreadsheets and draw graphs to explore a chemical buffer's ability to resist pH change, i.e., the *buffer capacity*. Quantification of buffer capacity is conceptually straightforward but involves multiple repetitive calculations. The key relationship is the Henderson-Hasselbalch equation:

which follows from the Law of Mass Action and

The spreadsheets automate many of the calculations, thereby simplifying the process. Instead of focusing on the calculations, students can see what buffer capacity means and focus on the a deeper understanding of its implications. After reviewing several buffer calculations, the stduents use the spreadsheet to investigate buffer capacity graphically and characterize blood's physiological buffer system. While solving the question of how many breaths one can take before alkalosis sets in, the students manipulate a logarithmic equation, do "what if" modeling, and analyze rates of change from plots of their cacluated results.

## Learning Goals

**Math and spreadsheets content**

- Manipulate multivariable equations involving logarithms.
- Use XY Scatter Plots to analyze chemical buffers and explore buffer capacity.
- Use a spreadsheet to model chemical buffers to determine buffer capacity through a "What If" process.
- Interpret a graph of the buffer system and relate the slope to buffer capacity.
- Relate numerical results to an applied problem in buffer capacity.

**Chemistry -- Buffers**

- Derive Henderson-Hasselbalch equation from the mass action equation for a weak acid. (Optional)
- Perform buffer calculations using the Henderson-Hasselbalch equation.
- Use a graphical approach to understand the behavior of chemical buffers.

## Context for Use

While the concept is often skipped, **Buffer Capacity** can an opportunity for students to apply and enhance their understanding of buffers.

This module is designed for use one lesson after buffer calculations are taught in a 1-year introductory college chemistry course. Students will see a brief review of three types of buffer calculations and then develop a spreadsheet to graph and explore concepts of buffer capacity.

Like other Spreadsheets Across the Curriculum (SSAC) modules, end of module questions activities are available.

## Description and Teaching Materials

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

## Assessment

The instructor's version also includes a pretest that can be used to evaluate the effectiveness of the module.

## References and Resources

- SSAC2006.Q199.CC1.2, "Is It Hot in Here? -- Spreadsheeting Conversions in the English and Metric Systems" by Cheryl Coolidge, http://serc.carleton.edu/sp/ssac/examples/14348.html.