Diffusion of Gases in Air
Purpose: The purpose of this lab investigation is to observe the diffusion of gases (as ions) in air. The experiment will demonstrate that the size of the ions influences the distance these ions move in a period of time.
Materials and Methods: The student will require goggles, cotton, a glass tube, paper labels, forceps, tin foil, two droppers, two 50 ml beakers, concentrated hydrochloric acid, and concentrated ammonium hydroxide.
Put on the goggles and carefully insert cotton plugs at each end of a glass tube. With great care, pour about 5 ml of concentrated hydrochloric acid and concentrated ammonium hydroxide in respective beakers. This should be done in a hood. If a hood is not available, be sure to have a room exhaust system turned on because these chemicals should not be inhaled nor should they touch your skin. Now using separate droppers, apply the chemicals to the cotton plugs. Hydrochloric acid is applied to the cotton plug at one end and ammonium hydroxide is applied to the cotton at the other end. Apply small labels at each end of the tube and cover the ends with foil.
Your setup should look something like the following:
Experiment: Allow about 30 minutes for the ions to diffuse within the tube. After that time, check for a white ring close to the hydrochloric acid end. This is a precipitate called ammonium chloride and is formed when ammonium ions react with chloride ions. Label the parts of the experiment in the above diagram.
Conclusion:
The molecular weight (sum of atomic weights) of the ammonium ion is 18 while the atomic weight of the chloride ion is 35.5. Given that, why is the ring of ammonium chloride closer to the hydrochloric acid end?
What is the relationship between size and diffusion?