Diffusion

Gupta, Raj                              Schurz High School
                                        794-8120
                      

Objectives:

1. To develop the concept of diffusion.

2. Demonstrate diffusion of molecules of matter in various states.             
           
Apparatus and materials needed:

Peppermint oil, potassium permanganate, evaporating dish, 250 ml. 
beaker, glasses, water, powdered drink mix, straws, raisins, pipette, spatula,
sandwich bag, marble and teaspoon.


Recommended Strategy:

1. Orally review the structure of the cell by using the sandwich bag
   filled with water and a marble to represent an analogy of the cell. The
   students know about the presence of openings in cell membranes and
   about the possibility of molecules moving through these openings.

2. To demonstrate diffusion, pour sufficient peppermint oil to cover 
   the bottom of an evaporating dish. As each student detects the odor, he 
   or she will raise his hand. Continue until all members of the class have 
   detected the odor of diffusing molecules. At the conclusion of the 
   demonstration, the air and oil molecules have spread out and mixed 
   evenly, they continue to bump and move. This spreading out is called 
   diffusion.
         
3. To observe diffusion of a solid, fill a 250 mL beaker with 
   distilled water and add several crystals of potassium permanganate. 
   Watch the results as the crystals settle to the bottom. Discuss this 
   phenomenon with the students. 

4. To observe diffusion of a liquid, place a glass of water at each 
   student's desk. Do not touch the water; keep the water still for this 
   test. Carefully drop a teaspoonful of powdered drink mix into the glass of
   water. Watch it for a few minutes without touching the glass. It will 
   go to the bottom and start diffusing.

5. To observe diffusion in raisins, place several raisins in a glass of 
   water. Let them sit overnight. Keep some raisins dry for a control. 
   Distribute to each student some soaked raisins and dry raisins. Let 
   them compare the two kinds of raisins and answer the questions on the 
   worksheet. 

Evaluation: 

Answer the following questions to show the understanding of diffusion.

1. What is diffusion?
2. Refer to the raisin experiment and explain the difference between the 
   soaked raisins and the dry raisins.
3. What is the evidence that something passed out of the raisins but
   not everything?
4. What is the difference between the bag's cell membrane and the raisin's
   cell membrane?.