Diffusion and Osmosis Theory

1. Begin with the concept of diffusion related to how particles of a substance spread out. 

[I will not dwell on traditional definition that is available from the textbook. Do make the connection between the definition and the concept/idea.]

Particles spreading out

Particles spreading out

2. Make it a concrete experience and allow the child to visualize particles movement.

Can you think of several daily examples of diffusion?

  1. When spaghetti is cooked, water particles diffuse into the spaghetti strings, making them thicker and more flexible.
  2.  Carbon dioxide bubbles in soft drinks diffuse out of your soda, leaving your soda flat.
  3.  A smelly gas i.e. flower fragrance, garbage stink, body odour, distributes itself over a room by diffusion, because gas particles moves from a region of high to low concentration.
  4.  A sugar cube in a glass of water that is not stirred will dissolve slowly and the sugar particles will distribute over the water by diffusion
  5.  A wilted carrot or celery made firm again by soaking in water. (Isn’t this known as osmosis? Osmosis is correct, osmosis is a “type”of diffusion – we will discuss that in a bit)
  6.  The smell of cookies diffuses through the house as they bake.
  7.  Perfume – perfume gas molecules diffuse into the air when put on so you can smell it.
  8.  Air freshener/deodorant – same concept as above. •
  9.  Teabag diffusion – tea leaf pigments diffuse through teabag to give the water its color and taste of tea
  10.  Cigarette smoke – it diffuses into the air and spreads throughout the room

3. Make the connection with Particulate Nature of Matter

Using item 4 – “A sugar cube in a glass of water that is not stirred will dissolve slowly and the sugar particles will distribute over the water by diffusion.”

Can diffusion occur for solids?

Sugar cube is a solid. However, when sugar dissolves in water, it forms sugar solution. It forms sugar solution. One region of the solution will be more concentrated than the rest and diffusion occur naturally.

(Dissolving is related to chemistry of solubility and can also be related to simple paper chromatography)

When will diffusion stop occurring? 

4. Expanding the concept of diffusion by introducing osmosis and active transport.


5. Finally, compare and contrast the process of diffusion, osmosis and active transport

Understanding the concept means that students can be familiar enough to compare and contrast

The next step is to Use the concepts and that is the real test if students have mastered the concepts.

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