Angela Patrick - Crown Academy

Somethin' Sweet

Angela Patrick                 Crown Academy
                               2128 South St. Louis
                               CHICAGO IL 60623
                               (773) 534-1680

Objectives:

Grades 3-8    (CAUTION:  THIS PROJECT REQUIRES MUCH ADULT SUPERVISION)

  Students will be able to:
A:  Synthesize a delectable delicacy from common chemicals:  create candy.
B:  Observe how molecules interact with each other in PHYSICAL CHANGES.
C:  Observe how the addition of heat can cause molecules to interact and form 
    new molecules in CHEMICAL CHANGES.  

Materials Needed:

  Per Group:
sugar            water             1 quart pot        whipping cream
measuring cups   stirring spoon    electric burner    candy thermometer
4 jars           large ceramic surface to cool        butter/margarine  
the candy        string            4 pencils

Strategy:

Student background knowledge is needed.  These lessons are to be used as part 
of a unit on matter and molecules.  Discuss and do other activities that helps 
students to understand that matter is made up of molecules.  

Molecules are the smallest particles of a substance of matter that will still 
have the same properties as the original substance.  Although a molecule is 
too small to be seen, chemists can still study how molecules interact with 
each other.  The making of candy will be a fun way to observe the changes in 
the states of matter:  from solids to liquids, liquids to gas, gas back to 
liquids, liquids back to a solid that is a different substance from that which 
was started with.

Demonstration:  ACTIVITY 1   CARAMEL CHEMISTRY

Place about 1/2 cup sugar into a deep nonstick pot.  Place the pan on the 
burner over low heat.  Continuously stir the sugar as you gradually increase 
the heat.  Have the students observe the sugar as it is being heated and 
describe what is occurring.  Eventually, the sugar will melt and break down to 
form carbon.  Keep stirring as you discuss because the sugar melts quickly and 
could start to stick and burn.  Caramel is a combination of sugar and carbon.
Remove the pan from the heat when the sugar is straw colored.  If you want to 
make delicious candy caramel, add whipping cream and butter slowly as you 
stir.  Taste the caramel.

The sugar has been converted to caramel through a chemical reaction.  If heated 
too long, the sugar turns the dark brown color of carbon and loses all of its 
sweetness - an interesting change, but not tasty.  The heat causes the sugar 
molecules to chemically change into a different substance, therefore it looks 
and tastes differently from the original white sugar.  

Student Group:  ACTIVITY 2    ROCK CANDY AND MOVIE GLASS

Put 1 cup of water into a pot on the burner.  Slowly add in 2 cups of sugar.  
Constantly stir over the heat until the sugar dissolves into the water.  
Slowly add up to another 2 cups of sugar (or as much sugar that will be 
dissolved into the water over the heat).  Remove the sugar from the heat 
before the solution reaches the boiling point.  Use the candy thermometer to 
make sure you have reached the temperature of 270 degrees.

MOVIE GLASS:

Pour the hot mixture onto the flat ceramic surface to cool.  In about an hour, 
the mixture will start to cool and harden.  This is the solution that 
hollywood movie-makers use to create the "glass" bottles and windows that the 
actors are hit with or thrown through.  The solid sugar molecules (crystals)  
dissolved into the water to become a liquid.  As the liquid cools down, the 
crystal molecules return to a solid that appears translucent.

ROCK CANDY:

Follow the directions above to heat the sugar.  Take the string and tie a 
paperclip to one end.  Tie the other end around a pencil.  Put the string into 
the jar and have it hanging towards the center from the pencil that is placed 
over the jar's opening.  Pour in the hot sugar solution.  Sit the jar in a 
cool and dark place for at least 2 days.  The students should begin to see the 
sugar begin to return back to the solid crystal form.  This time the sugar 
crystals will be larger than before but will be in the same form.  This is a 
Physical Change.

Performance Assessment:

Each child will be able to write a description of what is occurring to the 
sugar.  In this description, they must be able to state that the activity that 
involves dissolving the sugar into the water is a physical change that occurred 
when the sugar molecules became a liquid.  The liquid then turned into a gas 
as it boiled.  When the solution was poured into an item to cool, it returned 
to a solid.  

Each child must also describe the difference between the chemical change with 
the sugar over the heat, and the physical changes when dissolved into the 
water.

Conclusions:

The molecules of a substance of matter can be changed in two distinct ways.  
One is a physical change where the molecules can be returned back to the 
original form.  The second is a chemical change where the molecules react to 
form an entirely different substance.

References:
Book:  365 Science Projects
Internet:  SOAR (Searchable Online Archival Recipes)