Activities: Observing Using Sight
Suggested Grades K-6
Diffusion of a substance through a liquid
Amphibian absorption of water
The relationship between equilibrium and diffusion
20 to 30 minutes
How does diffusion occur in a liquid medium?
Diffusion is a basic concept of molecular movement that helps explain
the actions of many systems. It is particularly essential for understanding
the malformities observed in Minnesota's frogs as it is a process that
occurs through their permeable skin.
Molecules move from an area in which they are highly concentrated
to an area in which they are less concentration in a process called diffusion.
This process describes the movement of molecules through air, a liquid,
or in and out of a cell. It continues until the system reaches a state
of equilibrium in which the molecules are randomly distributed throughout
the whole system.
Static equilibrium exists when no action occurs.
Example: A Styrofoam cup full of water would be in static equilibrium
because the water level stays the same. If the cup had a hole at the
bottom water would leak out and the system would not be in equilibrium
Dynamic equilibrium exists when two opposing actions occur at the same
Example: If someone was adding to the cup above at the same rate that
it was draining out the bottom the system it would be in dynamic equilibrium.
The water level isn't changing but the actual water in the cup is changing.
Diffusion occurs when a system is not in equilibrium.
After completion of this activity students should be able to:
1. Describe how diffusion occurs within a liquid
2. Explain a situation where diffusion through a liquid might occur
in the natural world
A beaker or glass container of water
1. Tell the students that you are going to drop red ink into a beaker
of water. Ask the students to predict what will happen.
2. Drop the ink into the water. At first, the molecules of ink are bunched
together. But eventually the water molecules and the ink molecules bump
into each other and become mixed. The water turns red.
3. Have the students describe or draw the way that the ink molecules
move through the water. At first most molecules move in straight lines
away from the center of the drop. They change direction only when they
collide with each other or the water molecules. When they reach the glass
wall they begin moving back toward the center and past it toward the other
side. Diffusion stops when the molecules are evenly spread throughout
4. Explain that the system is now in equilibrium and diffusion no longer
How might diffusion help explain water pollution?
What factors might influence the rate of diffusion?
Is the system now in equilibrium?
Several factors affect the rate of diffusion. Kinetic energy is often
measured as the temperature of the system. Molecules in a higher temperature
system will diffuse more quickly because they have more energy and move
The size of the molecule is a second factor. A smaller molecule will
diffuse more rapidly because it takes more energy to get a larger molecule
Finally, any positive or negative charges on the molecule or the material
through which it is moving affects the rate of diffusion.
How could you test these different factors? Be careful to change only
one variable in each series of tests to make sure your results are scientifically
References and Resources
Julvet, Marice. 1993. The Fascinating World of Frogs and Toads.
New York: Barens Education Series.
Chinery, M. 1991. Life Story:Frog. Mahway, NJ: Troll Publications.
National Wildlife Federation. 1987. Ranger Rick's Nature Scope: Let's
Hear It for Herps. Washington, DC: National Wildlife Federation.
Click here for more information on how
this activity correlates with standards.
6 Science Application (Living Systems)
Content Standard C Life Science (organisms and environments)
Strand 1 Questioning and Analysis Skills
Strand 2.1 The Earth as a Physical System
Strand 2.2 The Living Environment
Return to Table of Contents