Determine How the Rate of Diffusion of a Material Is Affected by the Shape of the Container It's In

What You Need to Know

Diffusion is the movement of particles from one place to another. The rate of diffusion is the time it takes for particles to separate and spread evenly, forming a homogeneous mixture (a mixture that is the same throughout).

How Does Diffusion Work?

Diffusion is the spreading out of particles from a concentrated area. Diffusion occurs because the random movement of particles allows them to separate from one another. Two things that influence diffusion are the space between particles and the speed of the particles. The greater the space between particles and the greater their speed, the greater their ability to spread out from one another. The more packed the particles are in a substance, the more difficult it is for them to move, thus the more difficult it is for diffusion to occur. For example, solid substances are made of particles that are tightly packed together, so they diffuse very slowly. If you stacked a lead brick on top of a gold brick and left them undisturbed for several years, some of the gold atoms would diffuse into the lead brick and some of the lead atoms would diffuse into the gold brick, but most of the material would remain unchanged. On the other hand, the particles of liquids are less packed, move faster, and diffuse more quickly. For example, one drop of food coloring in a glass of water will noticeably diffuse throughout the water in minutes, or hours depending on the amount of water. The particles of a gas are much more distant from one another and move faster than either liquid or solid particles. It takes only a short time for gas particles to diffuse.

In fact, if the gas cannot be seen but has an odor, it is only the smell that indicates that the gas particles have spread. When a skunk sprays its musk, at first only animals and people near the skunk can smell it. In a short time, the odor can be smelled at great distances from the skunk.

What Does This Have to Do with How the Shape of a Container Affects Diffusion Rate?

Diffusion is the result of the motion of particles. Because of inertia (the property of all objects that resists a change in motion or direction), things in motion continue in the same direction unless some force stops them or changes their direction. When particles diffuse, their direction is changed when they bounce into one another, when they bounce into the particles of the substance they are diffusing through, and when they bounce into the sides of the container they are in. In a narrow container, particles diffuse faster because they bounce back and forth from the sides more often than in a wide container.

Experiment

Now, start experimenting with how the shape of a container affects the speed of diffusion.

Hints

• Find containers that are different shapes but about the same size.
• Diffusion of a colored solute in a colorless solvent is easy to see, and its movements are easy to measure.
• Use the same kind and amount of diffusing material (solute) and the same kind of solvent for each test.

FUN FACT

On Earth, gravity influences the diffusion rate of particles. In molten metals, temperature differences cause the warmer, less dense particles to rise and the colder, more dense atoms to fall. This movement of particles affects the diffusion process. In space, scientists have the opportunity to study diffusion in liquid metals without the effects of gravity. Therefore, they can determine the true diffusion rate in different liquid metals. This information could ultimately lead to better automotive, airplane, and building materials.

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