MUDDY WATERS: COURSE DESCRIPTION

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FIRST-YEAR EXPERIENCE PROGRAM
 

CAREERS IN EARTH SCIENCE

AVERAGE SALARY FOR GEOSCIENTISTS:  $79,160

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MUDDY WATERS
Chicago's Environmental Geology
Earth Science 109W, Fall 2010

INTRODUCTION TO COLORIMETRIC ANALYSIS

by Dr. Ken Voglesonger, Northeastern Illinois University

While you can see with your eyes if water is cloudy or clear, most of the substances that we are interested in testing water for are not visible to the naked eye. So in order to test for the presence of dissolved solids in water, we need to find a way “see” them. In this course, we will be using an instrument known as a colorimeter not only to determine the presence of specific dissolved solids, but also to quantify them, or figure out their concentration.

Colorimetry is simply the measurement of color. One of the tests you’ll be performing this week in lab is measuring the concentration of chloride (chemical formula: Cl
-1) in the samples that you collected at the North Branch of the Chicago River last week. Since the chloride dissolved in your samples is not visible, we’ll need a way to make it visible. This is done using chemistry. In general, a colorimetric procedure involves adding some type of chemical (or “reagent”) to a sample of water. The reagent then reacts with the substance we are trying to measure, causing a color change in the sample. In the case of the chloride test, we add silver nitrate to the sample. There is a chemical reaction that forms silver chloride, which makes the water cloudy (the color change!) Since we not only want to know if chloride is present in our samples, but also how much of it is present, the degree of color change due to the chemical reaction must be related to the concentration of chloride in the sample. The color change may be visible to your eyes, and we can use the colorimeter to make a precise measurement of the degree of color change.

A colorimeter passes light of a particular “wavelength” through the sample. Using a detector, the colorimeter can measure how much of the light has been absorbed by the sample. The amount of light absorbed by the sample is related to the color change caused by the chemical reaction. The amount of the absorption can then be used to determine the concentration of the chemical of interest (in this case, chloride).

For the tests we’ll be doing in this course, we’ll use an instrument called a Smart2 Colorimeter.  For each of the substances that we will be measuring, a detailed procedure gives step by step instructions for performing the test. In addition to this short introduction to colorimetric analysis, you have also been assigned to read the procedures for the analysis of chloride and sulfate (chemical formula: SO
42-)  for Friday’s class. While everything may not be clear at this point, by reading the test procedures, you’ll have an idea of what to expect in class this week. If you are curious about some other things, you can access the operator’s manual for the Smart2 colorimeters at http://www.lamotte.com/pages/common/pdf/instruct/1919manu.pdf

So besides this short introduction to colorimetric analysis, don’t forget to read the two test procedures also posted on the website: Chloride test procedure and Sulfate test procedure.


Department of Earth Science | Northeastern Illinois University

Copyright 2010 Laura L. Sanders.  Last updated September 12, 2010.

Your Instructors:
Dr. Ken Voglesonger

Dr. Laura Sanders

Your Peer Mentors:

Brian Dix

Sarah Paulis