Oxygen is in group 6 and period 2 of the periodic table. The atomic number of oxygen is eight and the electronic configuration is 2:6. According to Lavoisier, the name oxygen means “acid producer”.

Occurrence

Oxygen exists as a diatomic molecule (O₂) in air and make up about 21% of air by volume. It also exists as ozone (O₃) in the atmosphere. Oxygen also occurs in water and sand (SiO₂).

NB: Ozone is an allotrope of Oxygen.

Laboratory Preparation of Oxygen

1. Oxygen can be prepared in the laboratory by the decomposition of hydrogen peroxide solution using manganese dioxide as catalyst.

2H2O2 (g)→2H2O+O2 (g)

The gas is collect over water. It is dry by passing it through concentrated sulphuric acid or anhydrous calcium chloride.

NB: O₂ have almost the same density as air and so cannot be collect by displacement of air. It can only be collect over water.

2. Oxygen can also be prepared by the decomposition of potassium chlorate (KCLO₃). Heat is need in this case. It is dried by passing it through concentrated sulphuric acid or anhydrous calcium chloride and collected in a gas syringe.

2KCLO3 (l)→2KCL(s)+3O2 (g)

Physical Properties

• Oxygen is an odorless, tasteless and colorless gas.
• It is neutral and only slightly soluble in water.
• The density of oxygen is approximately equal to that of air. Therefore cannot be collect by upward displacement of air or downward delivery.