Colorful Sugar Water Density Tower
When density is the subject, going extra LARGE is the idea when you want a crowd to see the results easily.
This is one of those great demonstrations you could set up in the middle of a crowd and everyone would be able to see everything. If you’re looking for a simpler, more personal, or a one-on-one density activity, check out the Sugar Rainbow version. However, if your emphasis is LARGE as well as focusing on supersaturated solutions, this is the one you want to use. Yes, the two activities are very similar but this one feeds the crowd!
Fill the cups with 8 oz (237 ml) of hot tap water. Use your method of choice to color the water. You’ll want a different color for each cup, for example, blue, green, yellow, and red.
Add 2 level tablespoons (26 g or 3 sugar cubes) of granulated sugar to the first cup, 4 to the second cup, 6 to the third cup and 8 tablespoons to the fourth cup.
Be sure to label each color with the amount of added sugar. For example:
- Blue = 2 tablespoons
- Yellow = 4 tablespoons
- Red = 6 tablespoons
- Green = 8 tablespoons
Use a separate spoon to stir each cup and stir until the sugar is completely dissolved. It’s crucial that all of the sugar be dissolved in each cup. Use separate spoons so you don’t dilute one density with another.
It’s likely, however, that you’ll reach the saturation point of sugar in a cup of water by the second or third cup. You’ll stir and stir but there seems to always be some sugar remaining undissolved in the cup.
You’ll need to move to a supersaturated solution to dissolve all the sugar and this means heating the water. Place a cup in a microwave oven for 20 seconds to warm the water. Stir the warmer water. Continue warming and stirring in stages until all of the sugar is dissolved in all of the cups.
Start with the cup containing the most dissolved sugar (green water in the example). Using a pipette, dropper, or a turkey baster, add the bottom layer of colored sugar water to the jumbo test tube. Keep the sides of the test tube dry by placing the baster well down into the center of the tube before gently squeezing it.
Adding layers is challenging. The tendency is to rush and that simply mixes batches of sugar water in the test tube causing separate color layers to disappear. NOTE: If you have only one pipette or baster, be sure to rinse and dry it between each color change so one solution doesn’t mix with another.
Using a new pipette, carefully add the next density layer (red in the example) onto the surface of the first. The best technique is to keep the tip of the pipette against the wall of the test tube and a little above the surface of the rising sugar water. Slide the pipette up the wall as the level rises, too. This will take a lot of patience so squeeze slowly. Add as much of this color as you did of the first one.
At first, the colors may seem to mix a little no matter how careful you are. Then, as more of the second color fills the test tube, a separation will appear. The less dense solution is floating on top of the more dense solution.
Use a new pipette to continue with the next color the same way. Grab a fourth pipette to finish with the least dense color until you have stacked all of them on top of each other in the tube. Admire your work and look for more colors in the tube than you had at the start.
How Does It Work
Keep in mind that this activity takes a lot of patience. You won’t see the color you’re adding right away. Just keep carefully squeezing the sugar water solution into its layer and you’ll see it begin to stack up.
Density is the measurement of how much “stuff” is packed into a measured space. That’s how we get the equation for density: Density = Mass (the stuff) ÷ Volume (a measured space). Nearly every substance and material imaginable has a different density. This is especially true for the sugar solutions you made.
By increasing the amount of sugar in solution but keeping the amount of water constant, you created solutions that have increasing densities. As you add sugar to the water, more and more sugar molecules take the available space between water molecules, making the solution more dense. The cup containing eight tablespoons of sugar will be the most dense and the cup with two tablespoons will be least dense. As you can see, a solution with a lower density stacks on top of a mixture with a higher density.
How did you make a supersaturated solution? When you dissolve sugar in water, there’s a point beyond which no more sugar can dissolve. This is called a saturated solution. The available water molecules have grabbed the most sugar molecules they can. However, if you heat this solution (add energy to it), the water molecules move much faster and more sugar can be dissolved. When this solution is cooled, the sugar remains in solution and it’s called a supersaturated solution. However, it’s very unstable and the sugar will crystallize very easily with very little effort. A stray sugar crystal, a bump, or a random nucleation site can spur very rapid crystal growth.
Take It Further
What happens if you shake or mix up the finished sugar density column? What will the colors do? When you’re ready, try it. The colors will not separate again and go back to the the layers you see before you shook it. Remember, it’s all just sugar water and not at all like a water and oil density tower. The various sugar waters will mix evenly and you end up with a very dark-colored, sweet syrup.
Use different solids to dissolve in water. See what you get using baking soda, salt, flour, or cornstarch. Do a test using oil and sugar to see if you can build a density tower similar to the sugar water version. The science never quits!