# Rate of Diffusion

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#### Updated on Nov 18, 2013

Ever notice that when you pour a darker liquid into clear water the overall color changes into a shade between both? Diffusion is the passive process of particles spreading from areas of high concentration to areas of low concentration until they become evenly distributed throughout a space. We call diffusion passive because it requires no input of energy to occur: it’s caused by Brownian motion, the seemingly random movement of particles within liquid or gas.

So what explains Brownian motion? Even though you can’t see it happening, all atoms vibrate ( and the hotter they are, the faster and harder they do so). Because vibrating atoms in fluid (a liquid or gas) are in close contact with each other, they bump each other around as they collide. Over time, it’s easy to see how two gasses or liquids can get all mixed up when put in the same container. The rate of diffusion refers to how quickly or slowly this process happens.

In this experiment, we will first be looking at how diffusion occurs in hot and cold homogenous mixtures. A homogenous mixture is one that is made up of materials that are evenly distributed throughout the mixture. Using food coloring as our solute, or material to be dissolved, we will watch and observe the rate of diffusion occurring in both hot and cold water solvent. Then, we can explore how the shape of a container affects the movement of particles.

### Problem

How is diffusion affected by hot and cold temperature, and why does the shape of the container make a difference?

### Materials

• Food coloring (red & blue)
• 2 clear glass cups of the exact same size and shape
• 2 differently shaped clear containers (narrow and wide), preferably about the same size

### Procedure: Temperature Difference

1. Fill one glass cup with hot water. Fill the second glass cup with cold water.
2. Drop 1-2 drops of red food coloring in the hot cup, and 1-2 drops of blue food coloring in the cold in the cold one.
3. Watch and wait for color to disperse entirely.

### Observations & Results

You should have noticed that the red food coloring in the hot water dispersed much more quickly than the blue food coloring in the cold water did. This is because particles vibrate faster and harder when they’re warmer—the hot water molecules struck the food coloring molecules harder and more frequently, scattering them until the cup ended up containing a homogeneous solution.

### Procedure: Differently Shaped Containers

1. Fill both containers with the same temperature of water.
2. Drop one drop of food coloring in each of container and compare their rate of diffusion.

### Observations & Results

The narrowest container will likely have demonstrated the slower rate of diffusion because fewer molecules are in contact with each other, meaning fewer collisions of the solvent with the solute.

### Conclusions

Temperature and the shape of the containers affected the rate of diffusion in both experiments. Particles move faster in warmer water, so the red coloring spread more quickly through the cup. The narrow shape of the containers used in the second experiment slowed down diffusion because of the container’s effect on Brownian motion (the mechanism behind diffusion).