Relative Evaporation Rates

Two watch glasses are placed on an overhead projector. A drop of water and a drop of acetone are placed on separate watch glasses and observed. The drop of acetone evaporates much faster than the drop of water. 

Curriculum Notes 

This demo is probably best used when discussing intermolecular forces. One day of lead time is required for this project. 

Lead Time 
One day of lead time is required for this project.
Discussion 

Acetone evaporates much faster than water, even though its molecular mass is more than three times as much. Water is capable of hydrogen bonding, whereas acetone is not. The relatively strong hydrogen bonding between the water molecules slows the evaporation rate and increases the surface tension, as evidenced by acetone's flatter drop shape on the watch glass.Thanks to Julie Haack of the University of Oregon Chemistry Department for coming up with this demo. 

Materials 
  • overhead projector and screen
  • two small watch glasses
  • Two dropper battles, one containing water, the other containing acetone
Procedure 

The two watch glasses are placed on the overhead projector. A drop of water and a drop of acetone are placed on separate watch glasses and observed. The drop of acetone evaporates much faster than the drop of water. 

Safety Precautions 

Acetone is very flammable. Take appropriate precautions.Potential Health Effects of acetone: Inhalation - Inhalation of vapors irritates the respiratory tract. May cause coughing, dizziness, dullness, and headache. Higher concentrations can produce central nervous system depression, narcosis, and unconsciousness.Ingestion - Swallowing small amounts is not likely to produce harmful effects. Ingestion of larger amounts may produce abdominal pain, nausea and vomiting. Aspiration into lungs can produce severe lung damage and is a medical emergency. Other symptoms are expected to parallel inhalation. Skin Contact - Irritating due to defatting action on skin. Causes redness, pain, drying and cracking of the skin. Eye Contact: - Vapors are irritating to the eyes. Splashes may cause severe irritation, with stinging, tearing, redness and pain.Chronic Exposure - Prolonged or repeated skin contact may produce severe irritation or dermatitis.

© Copyright 2012 Email: Randy Sullivan, University of Oregon Chemistry Department and UO Libraries Interactive Media Group