Flow of Gases Through a Porous Cup
Description: When a porous cup is immersed in air, no net gas flow occurs. When immersed in a gas lighter than air, a net inflow occurs. The rate of diffusion into the device depends on the molar mass of gas. When immersed in a gas heavier than air, net outflow of gas is observed.
This demonstration is also available on video and JCE Software “Chemistry Comes Alive!” CD-ROM Vol. 1
Source: Shakhashiri, B.Z. “Chemical Demonstrations: A Handbook for Teachers”
Year: 1985 Vol: 2 Page: 54
Keywords: Diffusion, Porous cup, Kinetic Molecular Theory, Molecular speeds
Rating: 
Hazard: Low
- Use of inert materials
- Breakage hazard
- Asphyxiation hazard
Effectiveness: Good
- Good connection from demo to course material
- Clear contrast between behavior of systems
- Mild effects are seen by audience
- Time to results is low
- Moderate reliability
- Results are observable with guidance
Difficulty: Medium
- Some sequential manipulations
- Precise manipulations are required
- Some intermediate steps to results
- Use of pressurized gas
Safety Precautions:
- Eye protection required
- Perform in a well ventilated area
Class: Gases, Kinetics
Division: General, Physical Chemistry
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