======Ammonia and Hydrogen Chloride Diffusion======


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**Alternative titles:** Comparing Gas Diffusion Rates
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====Summary====                   
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====Procedure====  
  - Place a long glass tube horizontally on a retort stand and secure it with clamps.  
  - Soak a small ball of cotton wool with aqueous ammonia and insert it a few centimeters into one end of the tube, sealing with a rubber bung.  
  - Using rinsed tweezers, soak another cotton ball with concentrated hydrochloric acid and insert it into the opposite end of the tube, also sealing with a bung.  
  - Leave the tube undisturbed and observe over 15–20 minutes.  
  - Watch for the formation of a white ring of ammonium chloride where the two gases meet. Note its position relative to each end.



====Links==== 
Ammonia and hydrogen chloride diffusion experiment - Nigel Baldwin: 
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📄 Diffusion of ammonia and hydrogen chloride gas - Institute of Physics: [[https://spark.iop.org/diffusion-ammonia-and-hydrogen-chloride-gas]]\\

====Variations====
  * Try using tubes of different lengths to see how the time for ring formation changes.  
  * Instead of a tube, put ammonia and hydrochloric acid in two separate small beakers, then cover them with an inverted larger beaker.
  * Leave the experiment overnight in the fumehood.


====Safety Precautions====
  * Wear safety goggles and a lab coat.  
  * Conduct the experiment in a well-ventilated lab or outdoors, as both ammonia and HCl vapors are irritating and corrosive.  
  * Handle concentrated hydrochloric acid and concentrated ammonia carefully; avoid skin and eye contact.  
  * Dispose of cotton wool safely in a fume hood after use.  
  * Rinse tweezers after handling each cotton wool sample to avoid corrosion or cross-contamination.




====Questions to Consider====
  * Why does the white ring of ammonium chloride form closer to the hydrochloric acid end? (Because ammonia molecules, being lighter, diffuse faster than hydrogen chloride molecules.)  
  * How does this experiment provide evidence for the particle model of gases? (The movement and eventual meeting of invisible particles is inferred from the appearance of the solid ring.)  
  * Why do lighter molecules move faster at the same temperature? (Because the average kinetic energy is the same for all particles at a given temperature, so lighter particles must have higher speeds.)  
  * What is the balanced equation for the reaction observed? (NH3(g) + HCl(g) → NH4Cl(s).)