Topic 1 - Gas preparation and identification

OXYGEN

• You can make oxygen by warming hydrogen peroxide on its own very gently, or at room temperature using manganese(IV) oxide to catalyse the decomposition. Oxygen can be collected over water. 

Test for oxygen

Light a splint and blow out the flame, so that it is just glowing. If this is placed in oxygen, the flame will relight.

AMMONIA

• Any ammonium salt in aqueous solution can be warmed with any alkali. Any alkali can be used because ammonia solution is a very weak base and can be displaced from its solution by a stronger one. 
• A ‘tower’ of quicklime can be used instead. Remember that ammonia is so soluble in water that it can, under no circumstances, be collected over water.

Test for ammonia

The smell is one clue, but not a legitimate test. Damp red litmus paper should be held in the gas. Ammonia will turn it blue, because it is strongly alkaline.

It also forms white fumes of ammonium chloride if a rod that has been dipped in hydrochloric acid solution…