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Relative Velocities of NH₃ and HCl


  • Both HCl and Ammonium Hydroxide are corrosive and toxic. Avoid exposure.
  • Avoid breathing the ammonium chloride.

Chemicals and Solutions

  • Conc. HCl (hydrochloric acid)
  • Conc. NHOH (aqueous ammonia)


  • Special 250 ml Erlenmeyer flasks with 34/35 and special stopper with fritted glass tips (2)
  • Supporting stands & clamps
  • Meter stick


  1. Assemble stand and clamps; mount cell horizontally.
  2. Label flasks, "HCl", "NH".
  3. Fill appropriate flask with conc. reagents to point that will cover fritted tip.
  4. Quickly but gently (to minimize air disturbance in tube) insert flask tops into ends of tube at the same time. Make sure there is a tight seal or air currents will disrupt experiment.
  5. A ring of NHCl (ammonium chloride) will form where the gases meet. This may take several minutes.


The distances from the fritted glass tips to the fog will be proportional to the velocities. This experiment demonstrates Graham's Law which states that the rate of diffusion of a gas is inversely proportional to the square root of its molar mass.