Diffusion in Hot and Cold Water

By adding food coloring to hot and cold water, students can observe that molecules in hot water move faster, causing the dye to spread more quickly.

1. Fill one glass halfway with very cold tap water.
2. Fill another glass halfway with very hot tap water.
3. Predict how the food coloring will behave differently in hot and cold water.
4. At the same time, add 2–3 drops of food coloring into each glass without stirring.
5. Observe how the food coloring spreads in each glass. Compare the differences in diffusion rates.

Demonstration - Hot & Cold Diffusion - Mr Z Physical Science:

Food Coloring + Hot and Cold Water - Scott Milam:

📄 Hot and Cold: Molecules in Motion - Liberty Science Center: https://lsc.org/news-and-social/news/hot-and-cold-molecules-in-motion

• Heat or cool the food coloring itself in a water bath before adding it to water to see if its temperature affects diffusion.
• Compare results using salt water instead of plain water.
• Try the experiment with other liquids such as oil, vinegar, or juice to see if diffusion behaves differently.
• Test how stirring affects diffusion compared to letting it occur naturally.

• Adult supervision is required when handling hot water.
• Be careful not to spill water or food coloring on skin or surfaces.
• Clean up spills promptly to avoid staining.
• Pour water down the sink and wash glasses thoroughly after the experiment.

• Why does the food coloring diffuse faster in hot water than in cold water?
• How does molecular motion explain the difference between hot and cold water diffusion?
• How is diffusion important in the human body, for example in oxygen exchange in the lungs?
• Would the diffusion rate change if the water volume or container size were different?