Laboratory Preparation of Ammonia (NH₃)
Heating ammonium chloride with calcium hydroxide · collected by downward displacement of air
🧪 Apparatus Required
- Hard-glass test tube (mouth tilted down)
- Bunsen burner with flame
- Retort stand and clamp
- Delivery tube
- CaO drying tower
- Inverted gas jar (mouth down)
📝 Chemical Reaction
2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3↑
Ammonium chloride reacts with calcium hydroxide on heating to give calcium chloride, water vapour and ammonia gas.
💡 Key Points
- NH₃ is lighter than air → collected by downward displacement of air (jar inverted, mouth down)
- Colourless gas with a pungent smell
- Turns moist red litmus blue
- Highly soluble in water — so it cannot be collected over water
- Test tube mouth is tilted downward so that water produced does not crack hot glass
⚠️ Safety Precautions
Work in a fume hood · NH₃ is toxic and irritant · do not inhale directly · handle hot glassware with tongs · keep the delivery tube clear of the gas jar mouth.