6.1 - The Diffusion Chamber

HandsOn Activities:

22. The Diffusing Checkers Model

23. Deriving the Motion of Molecules

24. Diffusion Chamber

25. Location of the Precipitation Point


15. The Diffusion Chamber Simulation

Ammonia gas is invisible as it moves through the air from Barry's opened bottle to Jennifer's nose. There is a simple demonstration that makes visible some consequences of this motion of ammonia. The demonstration uses what is called a diffusion chamber. This is a popular chemistry experiment in which two different gases, typically ammonia (NH3) and hydrogen chloride (HCl) diffuse from opposite ends of a closed glass tube (Figure ). Eventually the two gases meet and react, forming a disk of white dust made of the solid ammonium chloride (NH4Cl). We say that the ammonium chloride is precipitated out of the gas.


Figure 6.2: Diffusion Chamber Demonstration. The acid hydrogen chloride HCl (in water) is placed at one end, and evaporates as HCl gas. Ammonia, which is a water solution of ammonium hydroxide, is placed at the other end, and gives off ammonia gas, NH3. The two gases diffuse down the tube. Where these gases first meet, they react chemically to make a disk-shaped cloud of dust composed of (the solid) ammonium chloride NH4Cl.

Later you will be able to perform this experiment using small tubes supplied in your laboratory kit.

Q6.2: Guess where along the tube the disc will form and how long a time it will take before the disk appears. Write down your guesses.

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