Practical work 3. Preparing ammonia and experiments with it
The aim of the practical work is to prepare ammonia, collect it and prove its properties. A mixture of ammonium chloride and slaked lime releases ammonia when heated: 2NH₄Cl + Ca(OH)₂ → CaCl₂ + 2NH₃↑ + 2H₂O. Ammonia is lighter than air, so it is collected in a tube held mouth down. To prove the gas there is no need to smell it: a moistened red litmus paper held near the tube mouth turns blue, and phenolphthalein dropped into an ammonia solution turns it deep crimson (NH₃ + H₂O ⇌ NH₄⁺ + OH⁻). When a tube full of ammonia is lowered mouth-down into water, the water rises inside: ammonia dissolves extremely well. A glass rod wet with concentrated HCl brought near the ammonia gives white smoke (NH₄Cl): NH₃ + HCl → NH₄Cl. With acids ammonia gives salts (NH₃ + HNO₃ → NH₄NO₃). All experiments are done by the teacher in a fume cupboard or under supervision, in goggles and gloves; nobody smells the ammonia, the mixture fills only a third of the tube, and heating is done carefully. In this lesson you prepare the plan, a table and the equations.
“Lab notebook”: draw a table for 5 experiments: preparing ammonia, collecting it, proving it with an indicator, dissolving in water, smoke with HCl vapour. For each note which indicator colour change is expected and write “why we do not smell it”. Only a table and cards; no substances are used.