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.
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.
Laboratory Method : In laboratory, dioxygen gas can be prepared by thermal decomposition of potassium chlorate.
By Heating Metallic Oxides : On heating the oxides of mercury, lead, silver, managenese etc. dioxygen is prepared.
By decomposition of Peroxide : Hydrogen peroxide is decomposed easily in presence of finely divided metals or manganese dioxide
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
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.
→ 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.
→ 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.
From Sodium Peroxide Dioxygen can be prepared in laboratory by the action of water on sodium peroxide.
2Na2O2 + 2H2O → 4NaOH + O2
Dioxygen can also be prepared by the action of acidified potassium permanagate on sodium peroxide.
2KMnO4 + 5Na2O2 + 8H2SO4 → K2SO4 + 2MnSO4 + 5Na2 SO4 + 5O2
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
- It is paramagnetic in nature. Its paramagnetism is due to the presence of unpaired electrons. Its molecular orbital configuration is as follows:
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
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
Reaction with carbon, nitrogen and phosphorus
Reaction with sulphur
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.
With hydrogen chloride Dioxygen reacts with HCl in presence of cuprie chloride catalyst at 700 K.
With sulphur dioxide: In presence of oxygen SO2 la oxidised into SO2 at 728 K in the presence of V2O5 or finely divided platinum.
With carbon disulphide : Carbon disulphide on heating with dioxygen form sulphur dioxide and carbon dioxide.
With carbon monooxide: Carbon monoxide when oxidised with oxygen then carbon dioxide is formed
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
Oxidation Reaction. If hydrocarbona are oxidised in presence of catalyst, different products are formed. Here the oxidation is done in limited amount of oxygen
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.