Diffusion tube
Recreate the ammonia and hydrogen chloride experiment and predict where the white ring will form.
- Diffusion
- Relative molecular mass and speed
- Random particle motion
Ring position
59.4%
Speed ratio NH₃ : HCl
1.47
√(Mr HCl / Mr NH₃)
1.47
Predict
Where does the white ring of ammonium chloride form?
Experiment
- 1Run the experiment and note where the ring forms.
- 2Raise the temperature and run it again. Does the ring move, or just arrive sooner?
- 3Compare the speed ratio readout with √(36.5 / 17).
Explain
Diffusion is the net movement of particles from a region of higher concentration to one of lower concentration, caused by their random motion.
At the same temperature all gas particles have the same average kinetic energy. Since Ek = ½mv², lighter particles must be moving faster. Ammonia is lighter than hydrogen chloride, so it diffuses further in the same time and the ring forms nearer the HCl end.
Raising the temperature speeds up both gases in the same proportion, so the ring forms in the same place — just sooner.