Density Demonstration: Coke vs Diet Coke
by Liz LaRosa
updated 10.12.08
to list similarities of given objects
to brainstorm and find a solution as to why Diet Coke floats and Coke sinks
to define the term density
to see how much sugar we consume drinking one can of soda
Materials:
12 ounce coke can
12 ounce diet coke can
water
fish tank
sugar
nutra sweet
Procedure:
Pass the cans of coke around the room. Have each student take a good look at each can and ask them to make careful observations about what they see.
Ask the students to name as many similarities as they can about the 2 cans of coke. Make a list on the board.
Ask the students to list as many differences as they can about the 2 cans. Add to list
Some answers they may come up with......
Similarities 
Differences 


Place the regular coke into a small tank of water.
Place the diet coke into the water. (Look surprised and take both out. Have a student come up to verify that the cans are still sealed and have not been tampered in anyway!)
Place back into water. Ask the students to explain why one is floating.
Possible responses:
they weren't filled right at the plant
the red paint is heavier than the silver paint, or vice versa
one is flat, the carbon dioxide must have leaked out
nutra sweet is lighter than sugar
etc.....
The "Why":
Ingredients: http://www.thecocacolacompany.com/mail/goodanswer/soft_drink_nutrition.pdf
Show the students what 39 g of sugar looks like ( I found it effective to show the sugar in a small beaker while holding it next to the can so they can see how much space it would take up in the can) next to approx *188 mg (on an index card) of Nutra Sweet. Explain that ALL that sugar is in the regular Coke can, and that small amount of Aspartame in the Diet Coke can. Explain that a small amount of Aspartame is needed to make the Diet Coke sweet because it is so concentrated. Most students are surprised to actually SEE how much sugar there is!
Discuss how more "stuff" (matter) is crammed into the same amount of space, or VOLUME, and that increases the MASS. The relationship of Mass to Volume is Density. The more items (matter) you place into a defined space, the denser it becomes. For example, New York City is DENSELY populated because there are a lot of people in a small area. 20 people in an elevator is DENSER than 2 people in an elevator.
The Density of water is 1g/cm^{3}. An object will float is the density is less than 1. An object will sink if its density is greater than 1.
*Note: According to the Coca Cola company : 8 oz can has (125 mg) of aspartame . A can has 12 oz, so I approximated 188 mg for measuring purposes since my triple beam balance has a 0.1g bar. You can also say that there are 39,000 milligrams of sugar in a can of regular Coke!!!
Extension:
Weigh the Coke and Diet Coke to determine mass of each can. Using water displacement, find the volume of each can. Use the formula D=M/V and see if you can determine their densities. Is Diet Coke's density less than 1? Is regular Coke's density greater than 1?
Does this work for all Diet sodas? Try different brands, for example Pepsi, Dr. Pepper, Sprite, etc. Have the kids form predictions and test them out!