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Miscibility of Alcohol and Water (Mahya Babaie)


Mahya Babaie

Principle(s) Illustrated

  1. Structure of molecules are unique from one another. 
  2. Intermolecular forces of liquid
  3. Alcohol molecule structure 
  4. Water molecule structure 


  • 7.3.e. Students know that in solids the atoms are closely locked in position and can only vibrate; in liquids the atoms and molecules are more loosely connected and can collide with and move past one another; and in gases the atoms and molecules are free to move independently, colliding frequently.
  • 7.3.b. Students know that compounds are formed by combining two or more different elements and that compounds have properties that are different from their constituent elements.
  • 7.3.a. Students know the structure of the atom and know it is composed of protons, neutrons, and electrons.

Questioning Script

Prior knowledge & experience:

Students know the molecular structure of water. 

Students know that molecules are more loosely connected in liquid than solid. 

Root question:

Why does the volume of the water and alcohol mixture decreases?

                         Why the volume drops after mixing the 50 ml of water with the 50 ml of ethanol?

Target response:

It has to do with the molecular structure of water and alcohol. 

                        The reason why the total volume decrease is because Alcohol molecules are much smaller in size than the     
                        water molecules and as a consequence some of the ethanol molecules tend to cram in between the water 
                        molecules and hence you get a smaller volume

Common Misconceptions:

Some of the alcohol evaporates and therefore, the total volume decreases. 

Photographs and Movies

YouTube Video

The water and ethanol molecules are different sizes, with the ethanol molecules being smaller. Some of the ethanol fits in the spaces between the water molecules.

Think about two other materials: a liter of sand and a liter of rocks. If you pour the sand into the rocks, the total volume will be less than two liters, because some of the sand fills in the spaces between the rocks.