Experiment A-2

Classification:  Organization of Chemicals


In the previous experiment you tried to use several of your senses to describe a chemical substance (a candle) and the related chemical reaction (burning).  You may wish to refer back in your journal to note whether all of your observations were actually detectable directly by your senses, or whether a few may have required interpretation by thought processes.  We will often encounter this distinction between observation and interpretation as we study chemistry.  One of the reasons for its importance is that down through the centuries honest observations have turned out to be remarkably accurate.  But the history of science reveals that the interpretation of observations, while essential for living our lives, occasionally requires revision.  Even today there are often controversies about which alternate interpretations are more correct.  So distinguishing between observation and interpretation allows scientists to separate what we know for sure from what might be wrong and therefore deserves more cautious evaluation.

But this process of sorting into categories has broader uses for both chemists and for all humans.  Our senses flood us with more information than our brains are able to store or remember.  Our brains continually evaluate information from the senses, discarding unchanged or otherwise trivial observations.  But even the more significant observations would be overwhelming to remember.  So one of the skills we start developing early in life is to sort the observations into categories.  Some information is about dogs, some about trees, some about our home, and so forth.  Once sorted, we note much of the information is repetitious.  This allows us to interpret generalizations so we can forget most details while retaining the most useful.  For example, you don't need to remember the details of every tree you've ever observed but it is useful to remember what is generally true about trees.  In chemistry we use this classification process to help understand the billions of observations we make about the millions of different kinds of chemicals.  By sorting the chemicals in this world we make the process of understanding chemistry much easier!  Historically as chemists developed better classifications of chemicals, much improved understanding of the material universe also developed.  By leading you mentally through the same thought process, we are going to try to reproduce for you as an individual the improved understanding which society developed over centuries.


In this experiment you will classify a bunch of chemicals.
  1. Look around your home and pick out at least 20 chemicals.  (We are not going to consume these chemicals so you can put them back when finished with the assignment.)  Construct a list in your journal.
  2. Add to your list of chemicals the following: air, milk, some of your hair (you don't need to remove any), a piece of paper, an ink pen, laundry soap, some red wine, a cooking pan, and a towel.  It is OK if a few are duplicates of chemicals you selected.
  3. Invent a classification system in your journal which by asking a series of questions sorts the chemicals into different categories.  Each DIFFERENT kind of chemical should in the end be sorted into a different category.  It is acceptable to use different questions for different groups of chemicals.  Of course any identical chemicals will be sorted into the same category.

If you need course credit, use your observations recorded in your journal to construct a formal report.


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created 11/7/2002
revised 8/4/2004
link update 9/12/2005
by D Trapp
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