Dioxygen or oxygen preparation and properties, Group 16 P Block Elements

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements

Dioxygen (O2) :

→ Dioxygen is the most abundant element in the earth’s crust (46.5%). Karl Scheele was the first to prepare it by heating mercuric oxide in 1772. Later on Joseph Priestly also prepared it.

→ Lavosier first time named it oxypen for = acid. gennas-maker). In atmosphere, dioxygen (O2)is nearly 216 by volume and the rest is dinitrogen.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements

Preparation of  Dioxygen

Dioxygen can be prepared as shown below:

By heating the Salts Containing Oxygen :

The salts containing oxygen when heated strongly dioxygen is evolved.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 1

Laboratory Method : In laboratory, dioxygen gas can be prepared by thermal decomposition of potassium chlorate.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 2

By Heating Metallic Oxides : On heating the oxides of mercury, lead, silver, managenese etc. dioxygen is prepared.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 3

By decomposition of Peroxide : Hydrogen peroxide is decomposed easily in presence of finely divided metals or manganese dioxide

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 4

By the action of concentrated Sulphuric acid on certain oxygen compounds When concentrated sulphuric acid is reacted with some oxygen rich compounds then dioxygen gas is released

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 5

By photosynthesis : Oxygen gas can also be prepared by photosynthesis, taking place in the plants.

→ Industrial Preparation : Industrially dioxygen can be prepared by the following two methods: ) By electrolysis of water On clectrolysis of aedified water, using platinum electrodes or alkaline water using nickel electrode, dioxygen as is liberated at anode.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 6

→ By liquid air: First of all carbon dioxide and water vapours are removed from air then rest of the gases are liquified under high pressure and low temperature. This liquid air is now subjected to distillation then liquid dinitrogen (b.p. 77.2 K) distilled out first, leaving behind liquid oxygen (b.p.90 K). Now this liquid oxygen is recovered.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements

→ By electrolysis of Ba(OH)2 Pure dioxygen can be prepared by electrolysis of Ba(OH)2 Rolution using nickel electrode then oxygen gas is obtained at anode.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 7

From Sodium Peroxide Dioxygen can be prepared in laboratory by the action of water on sodium peroxide.

2Na2O2 + 2H2O → 4NaOH + O2

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements

Dioxygen can also be prepared by the action of acidified potassium permanagate on sodium peroxide.

2KMnO4 + 5Na2O2 + 8H2SO4 → K2SO4 + 2MnSO4 + 5Na2 SO4 + 5O2

Properties :

Its physical and chemical properties are as follows:

Physical Properties of Dioxygen

  • It is colourless, odourless and tasteless gas.
  • It is neutral towards litmus paper.
  • It is slightly heavier than air. It is slightly soluble in water and its solubility is about 3.08 cm2 in 100 cm3 of water at 298 K and one atmospheric pressure. But this small amount of disolved oxygen is sufficient to sustain marine and aquatic life.
    It liquiefies at 90 K and freeses at 55K.
  • There are three isotopes of oxygen. They are
    Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 8
  • It is paramagnetic in nature. Its paramagnetism is due to the presence of unpaired electrons. Its molecular orbital configuration is as follows:

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 9

Chemical Properties of Dioxygen :

Some important chemical properties are as follows:

Action of Litmus Dioxygen is neutral to litmus.
Reaction with Metals except some metals like Ag, Au, Pt, it reacts with all other metals to for respective oxides. For examples,

Active metals like Na, Ca react at room temperature to form respective oxides.

4Na + O2 → 2Na2O
2Ca + O2 → 2CaO

Sodium also reacts with dioxygen at 575 K to form sodium peruxide

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 10

Magnesium burns in diexygen to form magnesium oxide

2Mg + O2 →2Mgo

Metals like Al, Fe reacts only on heating

4Al + 3O2 → 2Al2O3
4Fe + 3O2 → 2Fe2O3

Reaction with non-metals: It do not react with noble age. Some reactions with non-metals are as follows

Reaction with hydrogen

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 11

Reaction with carbon, nitrogen and phosphorus

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 12

Reaction with sulphur

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 13

Reactions with compounds : Dioxygen oxidises a variety of compounds. Some important actions are & follows

Reaction with aminonia as : Dioxygen axidises ammonia to nitrie oxide in the presence of platinum gauze catalyst at 1100 K.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 14

With hydrogen chloride Dioxygen reacts with HCl in presence of cuprie chloride catalyst at 700 K.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 15

With sulphur dioxide: In presence of oxygen SO2 la oxidised into SO2 at 728 K in the presence of V2O5 or finely divided platinum.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 16

With carbon disulphide : Carbon disulphide on heating with dioxygen form sulphur dioxide and carbon dioxide.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 17

With carbon monooxide: Carbon monoxide when oxidised with oxygen then carbon dioxide is formed

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 18

Reaction with hydrocarbons : Saturated as well as unsaturated hydrocarbone burn in excre of air or oxygen to form carbon dioxide and water. These reactions are known as combustion reactions. These reactions are exothermic in nature

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 19

Oxidation Reaction. If hydrocarbona are oxidised in presence of catalyst, different products are formed. Here the oxidation is done in limited amount of oxygen

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 20

Uses of Dioxygen

  • It is used in artifical respiration when it is mixed with helium or carbon dioxide
  • It is used as an oxidiser in the space rockets.
  • Liquid dioxygen mixed with finely divided carbon acts like dynamite in coal mining.
  • The isotope of oxygen (0-18) is used in studying the mechanism of certain reactions.
  • It is used in the manufacture of nitric acid, sulphuric acid, ethylene oxide, phenol, SO, etc. va) It is used in the production of oxy-hydrogen or xy-acetylene flame which is used in welding.
  • It is used as an oxidising agent in several reactions.
  • It is essential for the respiration by human being Dioxygen combines with our blood and forme oxy haemoglobin. In the form of oxyhaemoglobin it is carried to various parts of our body where it take part in oxidation reactions.
  • The energy releseed during oxidation reactions is quite essential to sustain life.

Chemistry Notes

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