Rubinah Atcha
227 600 160
EDUC 4537
Purpose: To demonstrate the space between molecules in liquids.
Grade: 11U and/or 12U Chemistry
Topic from Curriculum: This particular discrepant event can be applied to two topics in the
Ontario curriculum. It is a valuable introduction to grade 12 University topic Structure and
Properties. Matter is composed of molecules, but also empty space, which lends to physical and
chemical properties. This event can also be used for grade 11U Solutions and Solubility unit. The
polar nature of both liquids make them miscible and the way they hydrogen bond to each other
makes the volume decrease.
Theory: Matter consists of molecules constantly in motion and there is considerable space
between these molecules. In this discrepant event, alcohol molecules slip in between the spaces
around water molecules so that the total volume is reduced. Since both water and alcohol are
polar molecules, the slightly negative end of water (oxygen end) attracts the slightly positive
end of the alcohol molecule (hydrogen of the functional group) forming hydrogen bonds. In this
way, when alcohol dissolves in water, these molecules fit themselves in between water molecules
and the volume is reduced.
Materials: rubbing alcohol, water, graduated cylinder, food colouring (optional)
Procedure: Half fill a test tube (or graduated cylinder) with water. Then, fill test tube to rim
with rubbing alcohol. Cover mouth of test tube with your thumb and invert a few times to
encourage mixing of the liquids. The volume in the test tube should be visibly reduced. Proceed
with follow up questions below. Option: add food colouring to water.
Hints: Ask students simple addition questions (1+1=2, 5+5=10, etc.) Ask students what happens
when you take equal amounts of two liquids and add the two volumes together. Also, you can
make reference to how quickly money disappears; one moment you think you have a hundred
dollars but somehow you always have less that you think. Then perform discrepant event and let
students see how the volume of liquid decreases (liquids shrink). Ask students to hypothesize
what happened to the liquids. Did the water or alcohol evaporate? Was the water spilled when
the tube was inverted? Did the liquids shrink or contract?
Safety: Alcohol should not be ingested or heated (alcohol is flammable). Mixture is safe to
pour down the drain.
Reference: http://tiger.coe.missouri.edu/~pgermann/DiscEvent/ By: Mary Ann Shaefer