How to prepare oxygen in the lab.
Aim: To prepare oxygen in the laboratory using hydrogen peroxide and manganese (IV) oxide.
Apparatus: Flat bottomed flask, thistle funnel, delivery tube, trough, bee hive shelf and gas jar.
Materials: 20V hydrogen peroxide and manganese (IV) oxide.
1. The apparatus was arranged as shown in the diagram.
2. Some manganese (IV) oxide was put in a flat bottomed flask.
3. Using a thistle funnel some 20V hydrogen peroxide was poured over the manganese (IV) oxide.
4. When most of the water in the gas jar was replaced by gas, the jar was lifted carefully and the oxygen was tested using a glowing splint.
A colourless gas collected in the gas jar as the water level moved down. The water in the gas jar was displaced by the gas liberated from the decomposing hydrogen peroxide. The glowing splint was rekindled by the gas collected in the gas jar.
The gas collected in the gas jar must have been oxygen. Oxygen is colourless and odourless. So its presence had to be shown using a specific test with a glowing splint. A thin, long wooden rod is lighted using a match. The flame is spent out lightly such that the tip of the rod remains glowing. The latter is then inserted in the gas jar where oxygen is present. If the glowing tip rekindles it means that oxygen. Oxygen is the ONLY gas which supports combustion.
Oxygen was collected over water because it is quite insoluble in water. This method of collection is called collection by displacement of water.
During this experiment a decomposition reaction took place:
2H2O2(l) Manganese(IV)oxide 2H2O(l) + O2(g)
The manganese (IV) oxide was used as catalyst. A catalyst is a substance which speeds up the rate of a chemical reaction but remains unchanged at the end. The fact that they remain unchanged enables them to be used over and over again. So a little of the catalyst could be used indefinitely. Manganese (IV) oxide helped to speed up the decomposition of hydrogen peroxide. The reaction would have still taken place without it.