What conditions affect the diffusion of a substance in water?
Have you ever coloured a picture with marker and noticed that two touching colours begin to bleed together? In class, do you typically sit evenly spaced or all scrunched together? Although one of these refers to chemical properties and the latter social interaction, both are examples or diffusion.
Diffusion is the mixing of substances due to the movement of their particles. This can occur with all sorts of matter, but is most commonly observed in liquids and gases. Typically, diffusion refers to the movement of molecules from high concentrations to lower concentrations. The rate of this movement depends on the energy of the molecules. Think of how delicious smells from your kitchen take longer to get into your bedroom than to your living room which is located right beside the kitchen. That is because the molecules from the food odour haven’t diffused into that space yet. In this experiment, you will experience how temperature affects the mixing of food colouring drops with water.
The food colouring mixes through the hot water faster than it mixes with the cold water. This is because in hot water, the water molecules have more energy and are moving faster than the molecules of cold water. This makes it easier for the dye to get mixed throughout the hot water. Because diffusion happens from high concentration to low concentration, the more molecules are moving, the more opportunities they have to mix together. The high energy hot water model diffusion is important because it’s how we get oxygen to all the cells in our bodies. When deoxygenated blood is in your capillaries in your lungs, the oxygen in your lungs diffuses from a higher concentration in your lungs to the lower concentration in your blood. This allows red blood cells to carry oxygen all over your body.
Be sure to clean up when you are done. Wipe up any spills that may have happened. Pour all of the water down the sink, and wash out the glasses. Put the food colouring back where you found it.
In this experiment, the food colouring that gets added is the same temperature in each of the hot and cold water tests. Do you think the temperature of the food colouring might have an effect on how it diffuses? Can you find a safe way to heat or cool the food colouring before adding it to the water? Can you predict, based on the first way of doing the experiment, what might change, if anything?
Also, think about where you see this happen in other places. For example, how might this play into why coffee and tea always start with hot water? If you find an example of where hot or cold water is used for something that might involve diffusion, see if you can try it with the opposite and observe any differences in the results.
This experiment was selected for Science at Home because it teaches NGSS Disciplinary Core Ideas, which have broad importance within or across multiple science or engineering disciplines.
Learn more about how this experiment is based in NGSS Disciplinary Core Ideas.