Density Demonstration: Coke vs Diet Coke

by Liz LaRosa

updated 10.12.08




  1. 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.

  2. Ask the students to name as many similarities as they can about the 2 cans of coke.  Make a list on the board.

  3. Ask the students to list as many differences as they can about the 2 cans.  Add to list

  4. Some answers they may come up with......



  1. are made by the same company

  2. have the same shape

  3. made of aluminum

  4. are sealed shut

  5. have the same amount of liquid - 12 fl oz

  6. similar weights

  7. contain water

  8. contain carbon dioxide

  9. both have caffeine

  10. etc...

  1. one is red, the other is silver

  2. one is diet, one is regular

  3. one has nutra sweet

  4. etc...

  1. Place the regular coke into a small tank of water.

  2. 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!)

  3. Place back into water.  Ask the students to explain why one is floating.

Possible responses:

The "Why":


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/cm3.  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!!!


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!