# Calibrating a Pipettor

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 a virtual simulation of the procedure employed to calibrate laboratory micropipettors commonly used to measure and dispense small volumes (aliquots) of liquid (typically in the microliter range). Provided in the tutorial are four data sets (four hypothetical sample populations consisting of 10 aliquots each) representing multiple attempts to deliver the same preset volume. Students calculate the mean, standard deviation, and percent error for each of these four data sets. Then the students graph the calculated values to visualize the relationship of the data to the original preset volume. Based upon the results from the four different data sets, students determine the accuracy and reproducibility of the pipetting.

## Learning Goals

Students will:
• Consider the error inherent in numerical data.
• Design and organize spreadsheets to treat multiple sets of data.
• Determine cell equations to calculate the mean, standard deviation and percent error of a population of numbers.
• Generate several kinds of graphs.
• Interconvert volume and mass using the density of a substance.
In the process the students will:
• Learn how to do some basic calculations with Excel.
• Explore the relationship between density and temperature.
• Learn how to visualize data graphically.
• Learn how error shapes our appreciation for the value of data.
• Learn the definitions of accuracy and reproducibility (precision).
• Learn how Excel can be a powerful tool for analyzing complex data and an efficient tool for carrying out reiteritive 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 one of four that, together, serve early in the semester to familiarize students with the basic laboratory equipment at their disposal. The tutorial guides students through the logic and the calculations required of them in the laboratory report due at the completion of all four exercises. 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 do the pipetting exercise. 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

SSAC2005.QD451.WT1.1-student (PowerPoint 1024kB May27 10)

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

The module is constructed to be a stand-alone resource. It can be used as a homework assignment or lab activity. It can also be used as the basis of an interactive classroom activity. I typically use it as a prelaboratory tutorial to help students be better prepared for the laboratory exercise that it complements. Students who navigate easily in the Powerpoint environment and who have strong Excel skills manage the tutorial resonably well on their own. Students who have weaker computer skills will need some guidance to navigate the tutorial.

## Assessment

The last slide is an end-of-module assignment that can be used to examine student understanding and learning gains.

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