JCE Online Journal of Chemical Education
 | Subscriptions  | Software Orders  | Support  | Contributors  | Advertisers  | 

JCE Print
   Current Issue
 Previous Issues
 Supplements
 Search JCE Index

JCE Digital Library
   DigiDemos
 QBank
 SymMath
 WebWare

JCE Software
   Latest Releases
 Software & Video
 Downloads
 Support

Only@JCE Online
   JCE Online Store
 JCE HS CLIC
 JCE Discussion Forums
   Biographical Snapshots
 ChemEd Resource Shelf
 Featured Molecules
 Hal's Picks
 Project Chemlab
 Reviewed WWW Sites
 "Web-Ed" Articles

About JCE
   Features
 Publications
 Operations
 Outreach
 Contact Us


  Home > JCE Print > Journal of Chemical Education > Issues > 2002  > March  >
In the Laboratory
Two Experiments Illustrating the Importance of Sampling in a Quantitative Chemical Analysis
David Harvey
Department of Chemistry, DePauw University, Greencastle, IN 46135
Cover
March 2002
Vol. 79 No. 3
p. 360
Abstract
With many instructors of quantitative analysis courses emphasizing the analysis of "real-world" samples, there is a need for more experiments illustrating the importance of sampling as a source of uncertainty. Unfortunately, the few available experiments are either very lengthy or use instrumentation that is not widely available. This paper describes modifications to two previously published experiments illustrating the importance of sampling. The gross sample, a mixture of the acid-base indicator erythrosin B coated on crystalline NaCl, is analyzed spectrophotometrically after diluting individual samples with distilled water. The first experiment uses a four-level nested design to determine the contribution to the total variance of sampling, sample preparation, the spectrometer, and the sample cell's positioning in the spectrometer. The second experiment investigates the relationship between sampling variance and sample size. Each experiment can be completed in less than three hours. At first glance, the sample appears to be homogeneous and students are often surprised to discover that sampling is the greatest source of variance. This discrepancy between the expectation that sampling uncertainty is insignificant and experimental evidence to the contrary helps emphasize the importance of sampling.
Supplement
Copies of laboratory handouts, notes for the instructor, and sample data sets are available.
*  Contents JCE2002p0360W.doc (Microsoft Word)
*  Download
JCE2002p0360W.pdf

JCE2002p0360W.zip

JCE2002p0360W.sit
More Information
*  Citation
 Harvey, David T. J. Chem. Educ. 2002 79 360.
*  Keywords
 Analytical Chemistry; Laboratory Instruction; Quantitative Analysis; Statistics / Data Analysis
*  History
 Created:
Last Updated:		 January 31, 2002
March 16, 2005
<< Previous Article Table of Contents Next Article >>
  Home > JCE Print > Journal of Chemical Education > Issues > 2002  > March  > Page 360


Subscriptions
 Subscription Info
 Order Forms

JCE HS CLIC

Our Secondary School editors work hard to distill all the JCE materials to produce a fraction of particular interest to high school teachers. We call it CLIC.
 JCE HS CLIC

Contributions Welcome
JCE welcomes your submission
 Contributors' Corner

Advertisers
In recent years we have worked hard to better match our advertisers with our readers. When shopping for chemistry education materials, visit our advertisers' WWW sites first.
 Recent Advertisers

Be An Ambassador
Take JCE along on your outreach missions. Copies of the Journal, guest access to JCE Online, our publications catalog, and more are available for your participants.
 Outreach with JCE

Comments to
jceonline@chem.wisc.edu		 Copyright © Division of Chemical Education, Inc., American Chemical Society.
All rights reserved.