OXYGEN AND ITS COMPOUND: PREPARATION OF OXYGEN

OXYGEN AND ITS COMPOUND

Oxygen, the first element in group vi of periodic table has eight electrons which are distributed in orbital as follows

            1s²                                          2s²                                          2p⁴

                                                                        P_x        P_yP_z

It forms a wide range of ionic and covalent compound and it is the only element of group VI which forms multiple bonds with itself.

LABORATORY PREPARATION OF OXYGEN

Thermal decomposition of potassium trioxochlorate(v) (KClO₃): KClO_3, when heated releases all of its oxygen in the presence of MnO₂ as catalyst.

2KClO₃         ^MnO₂             2KCl_(s) + 3O_2(g)

Decomposition of hydrogen peroxide H₂O₂: H₂O₂ decompose in the presence of a catalyst, MnO₂, to liberate oxygen without heating.            

2H₂O_2(l)         ^MnO₂             2H₂O_(l) + O_2(g) 

INDUSTRIAL PREPARATION OF OXYGEN

Oxygen is prepared on a large scale by fractional distillation of air.

• Air is freed from CO₂ using caustic soda
• Followed by removal of dust particles and water vapour
• It is the compressed to about 200atm
• Then cooled compressed air is allowed to expand through a jet
• Cooled air is allowed to cool more with incoming air
• Continuous process of compression and expansion at temperature -220⁰C result in the liquefaction of air
• Liquefied air id fractionally distilled. Light noble gas are first obtained
• Follow by Nitrogen that boils at a temperature of -196⁰C (77K)
• It will remain oxygen that boils at -183⁰C (90K)

Oxygen is then dried, compressed, stored in steel cylinder.

Properties of Oxygen

Physical properties

It is a colourless, odourless and neutral gas.

It is slightly soluble in water

It is slightly denser than air

It has a low boiling point of -183⁰C (77K)

This makes it difficult to liquefy oxygen.

Oxygen solidifies at -225⁰C (48K)

Chemical properties of Oxygen

• It is stable to heat
• It does not burn
• Its solution in water is neutral to litmus
• It supports combustion very vigorously
• Direct combination with other elements:

With metals: Oxygen reacts with metals to give basic oxides.

4Na_(s) + O_2(g)                             2Na₂O_(s)

2Ca + O_2(g)                        2CaO

When sodium and potassium are heated in a plentiful supply, higher oxides are formed instead of the basic oxide.

4Na_(s) + 2O_(g)    2Na₂O₂

4K_(s) + 2O_2(g)                    2K₂O₂

Others metals that react/burn in oxygen are:

2Mg + O_2(g)                       2MgO

3Fe_(s) + 2O_(g)    FeO.Fe₂O₃

With Non-Metals: Oxygen combines with non-metal to form acidic oxide.

S_(s) + O_2(g)                    SO₂

P_4(s) + 3O_2(g)                       P₄O_6(s)

P4_(s) + 5O_2(g)                  P₄O_10(g)

C_(s) + O_2(g)                      CO_2(g)

• Most hydrocarbons burn in oxygen to form carbon(iv)oxide and water.

CH₄ + 2O_2(g)                CO_2(g) + 2H₂O_(g)

          Test for Oxygen

Oxygen rekindles a glowing splint of wood. Nitrogen(I)oxide is the only gas that has similar chemical test with oxygen.

Uses of Oxygen

1. Oxygen from air is used for breathing
2. Oxygen is used by divers
3. It is used for resuscitating fainting patients.
4. Oxygen is a component of oxy-ethyne flame which is used, in welding and cutting metals.
5. Oxy-hydrogen flame is used for cutting metals under water.
6. Liquid oxygen and fuels are used as propellant for space rockets
7. Oxygen is used in the steel industry for the removal of carbon, sulphur and phosphorus.
8. Oxygen is used in the Linz-Donawitz process for making steel.