Diffusion in a gas sim
Ammonia (Mᵣ 17) diffuses from the left, hydrogen chloride (Mᵣ 36.5) from the right.
Diffusion in a gas · covers the GCSE, IGCSE, O-Level topic
What the sim shows
Ammonia (Mᵣ 17) diffuses from the left, hydrogen chloride (Mᵣ 36.5) from the right. The damp indicator papers turn blue-purple where ammonia (an alkali) reaches them and red where hydrogen chloride (an acid) reaches them. Where the gases meet, NH₃(g) + HCl(g) → NH₄Cl(s) forms a white ring. It is nearer the HCl end: the rate of diffusion is inversely proportional to √Mᵣ, so in the same time ammonia travels √(36.5 ÷ 17) = 1.47 times as far. Warming the tube makes the ring appear sooner, but in the same place. The tube is 50 cm between the plugs; the clock runs 20 times faster than real time.
- Indicator: ammonia has arrived
- Indicator: hydrogen chloride has arrived
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