If you take a regular can of coke and a diet coke soda and place each (one at a time) into a container of water one will sink and the other will float at least generally speaking. This experiment is great for a classroom because you can try a wide variety of different products. You should be careful to look at the labels of each however to see that the volume given in milliliters is the same and the overall weight is the same. The cans are a certain volume and possible could hold more or less fluid, but if the fluid amount is the same then you are comparing the known volume and the known mass in grams.
The sugar molecule is actually quite a large and heavy molecule and can fit together in the same volume of space that the artificially sweetened soda would take and this means that it has a higher density per unit volume. If it exceeds the density of 1 gram per cubic centimeter it will be heavier than water and then sink, if it has a density of less than 1 gram per cubic centimeter it will float. (Note: This does not mean the diet soda will float like a boat on the surface of the water, but it may be peeking just above the surface a small amount..
Part of the problem with doing this experiment in a classroom is that you really need a very large and tall glass or clear plastic container that is only about 1/2 inch to an inch greater in diameter than the can itself. This will prevent the can from flipping on to the side. I have found such containers in some stores that sell a great deal of kitchen glassware and other glass products. You will also be dealing with a lot of water so you may want to place the tall glass itself into a large pan or tub to catch the overflow of water. You will only need to put enough water into the glass container to completely cover the can and still leave room for you to view it either sink or float.. I used two glass containers so I could try the sugared drink and the diet drink at the same time. I actually only compared the same product against the same produce, but a large number of different products could be compared.
As you put the can into the glass container it will “displace” water equal to its volume. This means that both cans should displace the same amount of water, but because they internally contain different liquids with different densities they should then either sink or float. I did this one time with about 20 different products that had a regular and a diet version and when the lab was over we went back to the classroom and drank the experiment. We never eat or drink in the lab and we washed the cans before we drank from them just to be safe.
Note: In science classes we sometimes calculate the density of pennies. We use a group of ten old pennies and 10 newer pennies in the calculations. They changed in composition over the years. You can check on the internet when they changed the composition.
