Teacher Notes



Author: Mary Harris: Missouri Polymer Ambassador
Video Editing: James Brownlow: George County High School

Recommended for Middle Level or Upper Elementary.

· This is a three day laboratory.
· All the polymers for this lab will grow to several times their original size when placed in distilled water for twenty-four hours.  The bears will also shrink back to their original size if they are placed in saturated salt solution.
· Gummy bears work the best since they are small and compact.  Worms tend to break when they are enlarged with distilled water.
· If your students observe and record mass changes, the handling of the bears must be gentle since the Gummy animals get quite flexible and fragile after twenty-four hours in distilled water.
· I tried Walgreen brand and Black Forest brand gummy bears and worms.  Both bear brands work well.  The Walgreen brand is larger.  Other brands just disintegrate.
· Saturated salt water is made from Kosher coarse salt so that it will be clear.  Make about one liter of solution for a class.  Start with one liter of distilled water and add Kosher coarse salt.  Shake until it dissolves.  Add more salt and shake.  It will take about 360 g or 1 3/4 cup of salt to make the solution saturated.  Allow plenty of time for the salt to dissolve.  This usually takes overnight!  When some salt remains undissolved this indicates saturation.
· Saturated sugar water will also work.  This is a bit sticky!
· Have extra gummi animals available for eating at a different time!  Do not allow eating during the laboratory$
· It is also possible to see a decrease in size from the original bear placed in saturated salt water.  I found a decrease in mass of 41% in 24 hours.
· To introduce the activity and the concept of diffusion, demonstrate the diffusion of a drop of colored dye in water or open a perfume bottle in the room.  The molecules move from an area of high concentration to one of lower concentration.
· Typical Data:
 
Original mass (g) Day Two mass (g) after DW % Change Day Three Mass (g)
after Salt
% Change
Bear 1.7 8.1 376 1.4 -18

 
 
Original volume cm3 Day Two volume cm3 % Change Day Three volume cm3 % Change
Bear 2.31 16.92 632 1.76 -24

Written by Mary Harris, Missouri Polymer Ambassador, email: mharris@jburroughs.org
Movie editing by James Brownlow from George County High School, Lucedale, MS
 
 

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