Discrepant Event Demonstration
1-cup water, 1 cup rubbing alcohol- Magic or Science?
Teacher Handout
Materials List:
 1 cup of Isopropyl Alcohol (rubbing alcohol)
 1 cup of Water
 3 measuring cups (2 8oz and 1 20oz)
Directions with safety consideration:
1. Fill one of the 8oz measuring cups with water and the other 8oz-measuring cup with
rubbing alcohol. Be careful and make sure the room is well ventilated because
rubbing alcohol has a potent smell. It is also VERY flammable.
a. Tell students not to perform this experiment at home without an adult!
2. Measure out both liquids over the sink, in case they were to spill.
3. Ask the class what they think will happen when the 2 liquids (rubbing alcohol and
water) are combined in the same container and what the volume will be. Why do
they think this? (Anticipated response: it will equal 2 cups because 1+1=2.)
4. Pour the 1-cup of water into the 20oz-measuring cup and then add the 1-cup of
rubbing alcohol.
5. Ask the class what happened? Was it the anticipated outcome/volume? Why do they
think this occurred?
6. Provide the teacher explanation below to the class.
7. Both liquids are made up of molecules, but the structure of the water molecules is
different from the rubbing alcohol molecules. The water molecules have spaces
between them that the alcohol molecules fit between. Because of this, the 2
different molecules fit together better than when they are alone, which makes them
take up less space (the smaller molecules slip between the spaces of the big
molecules). So, the two liquids mix together and make a solution with a volume that
is less than expected.
a. More in-depth response: The volume is less because of molecular bonding
(Hydrogen bonds). The OH- component of alcohol interacts with the H+ of
the water molecules. Because they attract each other they make “hydrogen
bonds.” Because of the tighter formation of the molecules, it reduces the
volume of the liquids combined.
Description of the use in an elementary classroom:
This activity meets the following Virginia SOLS: 5.4. It can be used to introduce a lesson on
matter, specifically liquids, atoms, elements, molecules, compounds, mixtures, and
solutions.
Resource Citation:
https://wow.osu.edu/experiments/States%20of%20Matter/Spaces%20Between%20Mole
cules
https://www.google.com/?gws_rd=ssl#q=rubbing+alcohol+and+water+added+together