LABORATORY AND INDUSTRIAL PREPARATION OF OXYGEN

SECOND TERM E-LEARNING NOTES

SUBJECT: CHEMISTRY

CLASS: SS 2

SCHEME OF WORK

WEEK 3

TOPIC: OXYGEN

CONTENTS:

1. GENERAL PROPERTIES OF OXYGEN, ELECTRONIC CONFIGURATION AND BONDING CAPACITY OF OXYGEN
2. LABORATORY AND INDUSTRIAL PREPARATION OF OXYGEN
3. PHYSICAL AND CHEMICAL PROPERTIES OF OXYGEN.
4. COMPOUNDS OF OXYGEN AND USES OF OXYGEN

PERIOD 2: LABORATORY AND INDUSTRIAL PREPARATION OF OXYGEN

LABORATORY PREPARATION

There are two general and common methods for the laboratory preparation of oxygen

1. Thermal decomposition of salts containing anions rich in oxygen, e.g. Potassium trioxochlorate(v) KClO_3(s).

The equation for the reaction is given as shown below.

2KClO_3(s) KCl_(s) + 3O_2(g)

2. Decomposition of hydrogen peroxide: In this case, no heat is applied to the decomposing substance, H₂O_2, but immediately, the MnO₂ touches H₂O_2, effervescence occurs releasing the gas oxygen as seen in the equation below.

2H₂O_(l) 2H₂O_(l) + O_2(g)

Dry oxygen gas is obtained by passing it through a woulf [wash] bottle containing conc. H2SO4; the gas is then collected by downward delivery (or upward displacement of air), since pure oxygen is slightly denser than air.

INDUSTRIAL PREPARATION

Oxygen is produced, in large quantity from the following sources.

1. From liquefied air: Oxygen is obtained industrially from atmospheric air by liquefaction, followed by fractional distillation of the liquefied air.

• Atmospheric air is purified by the removal of Carbon(IV) oxide, water vapour and dust.
• The purified air is compressed at a pressure of about 200 atmospheres, heated and then cooled. It is then allowed to expand suddenly, for further cooling.
• By successive heating and cooling, the pure air becomes liquefied at about -200 [73k]. This process is called LIQUEFACTION.
• The liquefied air is then fractionated by boiling. Nitrogen, being more volatile, boils first at – 196 [77k], leaving oxygen, which is about 99.5% pure. This separation technique is called FRACTIONAL DISTILLATION.[mediator_tech]

Liquefied oxygen is usually stored in cylinders for medical and industrial use.

1. By electrolysis: Oxygen, like hydrogen is obtained during the electrolysis of dilute H₂SO_4.

EVALUATION

1. State two main processes involved in the manufacture of oxygen from air.
2. Outline industrial production of oxygen from air.