Osmosis

Sandra E. Broomes              W. T. Sherman Elementary School
P. O. Box 20198                1000 West 52nd Street
Chicago IL 60620               Chicago IL 60609
(312) 238-7871                 (312) 535-1757

Objective:
            
To introduce 2nd grade students to the process of osmosis.
To learn how different kinds of solutions move through selectively 
   permeable membranes.
To understand the role of osmosis in the movement of molecules.
To remove the shell from a raw egg without breaking it.

Materials:

Supplies listed are for groups of 4 students to each group.

8 containers (clear plastic) for eggs
Vinegar
Water
Raw eggs
   

Plastic liter bottle (empty)
Small glass bottle with lid
Sand
Dry lima beans
Water

Beakers
Paper Towels
Labeling Tape
Distilled water
Apron

Strategies:

   The teacher will place the raw egg into the plastic container.  Do not crack 
the egg.  Cover the egg with the clear vinegar.  Then close the lid of the 
container.  Observe immediately and then periodically for the next four days.  
Each day add a new egg to a separate container following the same procedures 
listed above; using one egg each in a separate container.  Label the outside of 
each jar with exact date and time.  
   The movement of water across a differentially permeable membrane is called 
osmosis.  The molecules continue to move until equilibrium is reached (that 
is, equal concentrations of water molecules and of solute molecules on either
side of the membrane).
   The two experiments were used to show selectively permeable membranes which 
allow osmosis.  The membrane within an eggshell allows water to pass through in 
response to concentrations of the solutions on either side of the membrane.  The 
water will move toward the more hypertonic, or highly concentrated, solutions.  
To create the second experiment you mix 60% lima beans (by volume) and 40% damp 
soil.  Let the sand absorb all the water.  Place the pack mixture into a glass 
jar tightly (try to get rid of all the air spaces) all the way to the top of the 
jar.  Then seal the jar with the lid and place jar inside clear 2-liter pop 
bottle that has been cut off at the top wide enough to insert the glass jar.  
The pop bottle acts as a protection shield when the jar breaks.  The jar breaks. 

Conclusions:

Experiment One:
Bubbles start forming on the surface of the egg shell immediately and increase 
in number with time.  Each day the vinegar will cause the egg shell made of 
calcium carbonate to disappear and carbon dioxide bubbles to form.  The egg 
remains intact because of the thin see-through membrane around the outside.  The 
yolk can be seen through the membrane.  

Experiment Two:
Due to the process of osmosis - the dry lima beans are soaking up the water from 
the sand causing the beans to expand and break the jar.  This experiment shows 
how hot water poured into a glass jar with 60% dry lima beans and 40% sand will 
expand the lima beans-creating osmosis - THE JAR BREAKS.