We repeated this experiment on properties of matter from At Home Science.
We didn’t have a fancy test tube holder for our test tubes, so I fashioned them out of modeling clay.
- 3 test tubes or narrow glass containers
- Hot tap water
- Ice water
- 3 different colors of food coloring
- Supersaturated salt solution – boil a cup of water and add salt by a teaspoon at a time and stir to dissolve. Keep adding until you the salt no longer dissolves even with stirring. Let cool. You can talk about how heat allows for more dissolving of the solute (the salt), so it can “hold” more dissolved salt. *
- Add cold water to the first tube, hot water to the second tube, and the salt solution to the third tube. Label your tubes (ours had color coded lids so the blue lid was for the cold water, the red lid was for the hot water, and the yellow lid was for the salt water).
- Add a drop of food coloring at the same time to each tube and observe what happens.
You can see that the food coloring diffuses (spreads out) the fastest in hot water, the next fastest in the cold water, and doesn’t diffuse at all in the salt water.
Why does the food coloring diffuse faster in hot water than in cold water?
The molecules of the liquid move faster at higher temperatures, therefore diffusion happens at a faster rate when the liquid is heated.
Why doesn’t the food coloring diffuse in the supersaturated salt water?
Because the salt water is more dense than the liquid food coloring, therefore the food coloring just floats on top.
* You can use the leftover supersaturated salt solution to make salt crystals (you can use the same procedure as with growing sugar crystals)-
To download or print out a free working copy of this experiment, click on download or print on the image below.
Copyright 2009, by Casey and The Exploration Station.