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Lesson Overview
This activity focuses on reinforcing understanding of the concept of vapor pressure; it also demonstrates vapor pressure’s relationship to molecular structure and illustrates the importance of the phenomenon in real-world applications. The concept is brought to life through the story of how low-molecular-mass alkanes with high vapor pressures were causing apartment fires when impure kerosene was used in oil lamps in New York City in the 1870s.
Student Ability Level and Grouping
This activity is appropriate for high school chemistry students working in groups of two.
Expected Student Background and Skills
Students should already have a conceptual understanding of the phenomena of vapor pressure and gas pressure and of evaporation and condensation. They should be familiar with the units in which pressure is measured (e.g., mm Hg, atm, etc.), have a conceptual and mathematical understanding of Dalton’s law of partial pressures, and be familiar with the concept of molecular mass.
Time and Materials Required
The activity will take about 1 hour to complete. Materials and apparatus include:
Consumables
- Pentane
- Hexane
- Heptane
- Octane
- Methanol
- Ethanol
- 1-Propanol
- 1-Butanol
Non-consumables
- 25-mL Erlenmeyer flask
- 25-mL beaker
- Ring stand
- Clamp
- #5 Twist-it stopper
- Vernier temperature probe
- 20-mL syringe
- 1-L beaker
- TI-83 Plus or TI-84 Plus graphing calculator
Learning Objectives
After completing this activity, students should understand
- the concept of evaporation,
- the concept of vapor pressure, and
- how vapor pressure functions as an equilibrium phenomenon.
Students should also be able to appreciate
- the rough relationship between molecular mass and vapor pressure when dealing with compounds with similar molecular structures;
- the influence of other factors like polarity on vapor pressure; and
- the importance of vapor pressure in practical matters like fire safety.
In addition, students should be able to
- design an experimental strategy for determining the relationship between vapor pressure and molecular mass;
- determine trends in experimental data; and
- draw conclusions based on trends in experimental data.
National Science Education Standards
Science as Inquiry
- Abilities necessary to do scientific inquiry
Physical Science
- Structure of atoms
- Structure and properties of matter
- Chemical reactions
- Motions and forces
- Interactions of energy and matter
Science and Technology
- Understandings about science and technology
Science in Personal and Social Perspectives
- Natural and human-induced hazards
- Science and technology in local, national, and global challenges
History and Nature of Science
- Science as a human endeavor
- Nature of scientific knowledge
- Historical perspectives
Classroom activities are provided through the generous support of the Biogen Idec Foundation.