The Scientific Method Using Mystery Powders

Gail Gavin                     Chicago High School For Agricultural Sciences
                               3807 West 111th Street
                               Chicago IL 60655
                               (312) 535-2500

Objectives:

     The 6th grade student will be able to:
     1. Utilize the scientific process to determine the physical and chemical
        properties of a variety of common substances.
     2. Perform several chemical and physical tests for identifying substances.
     3. To construct and compare data results to determine unknown substances
        and mixtures.

Materials Needed:

Distilled Water            Toothpicks                  Possible Mystery Powders:
Paper Cups                 Iodine                         Boric Acid
Black Construction Paper   Clothes Pins                   Sugar
Lighter                    Vinegar                        Salt
Candles/Holders            Well Trays                     Baking Soda
Magnifying Glass           Droppers                       Baking Powder
Paper Towels               Aluminum Foil                  Flour
Conductivity Tester        If performing in classroom:    Corn Starch
Popsicle Sticks              Large Pan                    Powdered Sugar
    (marked 1/8th in.)       Squirt Bottles               Powdered Milk
                                                          Plaster of Paris
Two Identically Gift Wrapped Boxes-possible contents:
  Candy   Empty Aluminum Can

Strategy:
    
     Use a gift wrapped box as a motivational technique to introduce the 
scientific process/method.  Do activity "What's in the Box", correlating 
investigatory process with scientific method.  Introduce second identical box to 
class.  Ask question, because similar in appearance do they contain same 
contents?  Again discuss scientific process of discovery.  On large sheet of dark 
colored paper pour out sample of each mystery powder.  Have students imagine 
that they are chemists and one of the important tasks of a chemist is to make 
observations of unknown substances.  Every pure substance has a set of physical 
and chemical properties that distinguish it from other substances.  A physical 
property of a substance is that which can be observed or described aside from 
its chemical properties.  Examples of physical properties are color, state of 
matter (solid, liquid, and gas), texture, solubility, electrical conductivity, 
and melting point.  A chemical property involves listing or identifying chemical 
characteristics of a substance.  That is the substance's ability to react 
chemically with another substance and in the process create new physical and 
chemical properties.  The only way to observe a chemical property is by 
performing the chemical change.                   
     Performing several tests, the students will examine ten different 
substances by observing and recording their reactions to three different liquids 
(water, vinegar, iodine), electrical conductivity, and the effects of heating. 
     Pass out lab sheets and directions.  Point out appropriate lab safety.  
     Have students get into assigned groups.  As this is a beginners lab have
all necessary materials at their stations. 

                                 TESTS:
     Senses:
Ask students to use their senses of sight (with and without magnifying glass), 
touch, and smell.  Record data. 

     Solubility:
Put equal amounts of each powder into wells.  Add twenty drops of water.  Sample 
questions: "Did powders dissolve?  Is the water clear?  Is it cloudy?"  If 
solution is clear and substance has disappeared substance has dissolved.  If 
cloudy, substance is insoluble.  Record data. 

     Electrical Conductivity:
Utilize same tray wells.  Place tester wires into each well.  Make sure wires 
are cleaned after each test.  Record data.  Clean wells. 

     Iodine:
Repeat powder procedure.  Dispense two drops of iodine into each well.  Sample 
question: "Was there a change in color?"  Record findings.  Clean wells. 

     Vinegar:
Repeat powder procedure.  Dispense two to four drops of vinegar.  Sample 
question: "Did the powders fizz?"  Record findings.  Clean wells.  A fizzing 
indicates a chemical reaction. 

     Heat Test:
Make a cup out of foil.  Clip clothes pin onto cup.  Place small amount of 
powder into cup.  Place candle into holder and light.  Holding clothes pin place 
cup over flame.  Heat for up to two minutes if necessary.  Repeat procedure for 
each powder.  Sample questions: "Did any powders change?  Form new substances? 
Give off an odor?"  Record findings.  Use only dry powders to avoid splattering.  

     Upon completion of tests record findings on the board.  Ask students 
questions about their findings.  Were there any differences in the results? 
Discuss subjectivity, controls, variables, etc.  Have students give an 
operational definition of the powders at this point.  Example: "Powder two is a 
white, grainy, substance that fizzes with vinegar, turns iodine dark blue, does 
not dissolve in water and conducts electricity."  As students continue further 
testing on these powders they will form a more solid conclusion.  These Mystery 
Powders are a spring board to other labs such as testing for acids and bases, 
density, etc.  As a final activity open up mystery boxes and compare their 
conclusions to what is actually in the box.  This gives the students a feel of 
how scientists can identify and describe things they can not see. 

Performance Assessment:

     Combine non-reactive powders in equal proportions to make mystery mixtures. 
Have students rerun tests and record findings.  Compare prior results to 
determine what mystery powders constitute their mystery mixture. 

References:

Fitch, Dr. Thomas.  Mystery Powders Unit Plan.  Illinois State University.