Laboratory Preparation of Oxygen

Oxygen is prepared in lab generally in two ways either by the application of heat or no application of heat.
Using heat:
Oxygen in lab is prepared by heating the mixture of powdered potassium chlorate and manganese dioxide in the ratio 4:1 in a hard glass test tube. The oxygen gas is observed in a gas jar through the downward displacement of water. The reaction involved is given below:

2KClO3−→−−−−−MnO2200−300∘C2KCl+3O2↑

Preparation of oxygen on application of heat

Without heat:
The dry sodium peroxide is taken in a conical flask and the apparatus is fitted as shown in figure. The two necks of woulfe’s bottle is tighten up with cork so that no air enters from outside. It is connected with the delivery tube to a water trough containing water. Water is poured slowly from the thistle funnel. Here sodium peroxide reacts with water at ordinary temperature to give hydrogen gas. The hydrogen gas thus formed is collected in a gas jar through delivery tube by the downward displacement of water. The reaction takes place as below:

2Na2O2+2H2O⟶4NaOH+O2↑

Note: This reaction is very quick and hydrogen gas is collected in a gas jar within a fraction of seconds.

Preparation of oxygen without the application of heat