What is Dioxygen?

Dioxygen, one of the common allotrope of elemental oxygen, and it is represented with the chemical formula O2. It is generally known as oxygen, but to avoid confusion with elemental oxygen, it is also called dioxygen, molecular oxygen, or oxygen gas. Oxygen gas reacts with almost all the elements with the exception of noble gases.The resulting compound is known as oxides. Oxygen gas is very important for combustion, all though it is not flammable on its own. It is also a life-giving gas as mammals breathe in oxygen to live, as it helps to release energy.

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Laboratory Preparation of Dioxygen

There are numerous ways of preparing dioxygen in the laboratory.

  1. Catalytic decomposition of Sodium Potassium Chlorate with Magnesium dioxide as the catalytic produces dioxygen.

2KClO3  →  2KCl + 3O2 

This reaction occurs on heating, in the presence of MnO2 at 420K.

  1. Thermal decomposition of metal oxides with relatively low electrode potential in the electrochemical series like that of Mercury and Silver oxides etc. produces Dioxygen.

2HgO (s) → 2Hg (l) + O2 (g)

2PbO2 (s) → 2PbO (s) + O2 (g)

  1. Salts rich in oxygen, like nitrates and permanganates, produce Dioxygen when decomposed thermally.

2KNO3 2KNO2+ O2

2KMnO4 → K2MnO4  + MnO2 + O2

2NaNO3  → 2NaNO2  + O2

  1. The decomposition of Hydrogen Peroxide also produces oxygen and to increase the rate of decomposition, manganese(IV) oxide is added as a catalyst. 

2H2O2(aq) → 2H2O(l) + O2(g)

Industrial Production of Oxygen

There are two primary methods used for the industrial production of O2 from the air.

  1. Fractional distillation of liquified air with N2  distilling as a vapor while O2 is left as a liquid. Here liquid air is a mixture of liquid Nitrogen and liquid Oxygen. Nitrogen is more volatile because of the lower boiling point. It boils up first, leaving behind the pure oxygen. 

  2. Another method includes passing of clean, dry air through one bed of a pair of zeolite molecular sieves, which absorbs the N2 gas, and delivers the gas which is 90%-93% oxygen. 

Properties of Dioxygen

Physical Properties

  • It’s an odorless, colorless, and tasteless gas.

  • It is heavier than air with a density of 1.429 g/L.

  • It is slightly soluble in water, which is just sufficient to support aquatic life.

  • The melting point of oxygen is around 54.36 K and the Boiling point is around 90.188 K.

  • Oxygen exists in all three forms, i.e solid, liquid, and gas depending upon the temperature and pressure. 

Chemical Properties

  • It reacts directly with almost all the metals and non-metals to give oxides of their respective elements.

4Na + O2 → 2Na2O (With Metal)

C + O2 → CO2 (With Non-metal)    

  • It is paramagnetic in nature.

  • Oxygen normally does not react with acids and bases. 

  • Oxygen is a good oxidant and hence supports combustion. 

Fuel + O2 ⟶ CO2 + H2O

Example,   CH4 + O2 ⟶ CO2 + H2O

  • Oxygen, along with moisture, is responsible for the formation of rust on the iron.

Fe  + O2 + H2O  ⟶ Fe2O3n.H2O (Hydrated Iron Oxide)

Uses of Dioxygen

  • Dioxygen is vital for the respiration process.

  • It is used in oxygen cylinders which are used in hospitals and for mountaineering.

  • It is used for welding and cutting metals in the form of oxy-acetylene.

  • Oxygen gas combines with acetylene gas and produces an oxy-acetylene flame used for cutting and welding metals.

  • It is used in rocket fuel in liquid form. 

  • It is used in the production of Nitric acid.

  • It is used for artificial respiration mixed with Carbon dioxide or methane.

  • Oxygen is used in laser cutting. 

  • Oxygen is used in combustion processes. Materials that do not normally burn in air, burn easily in oxygen, so mixing oxygen with air enhances the combustion process. 

  • Oxygen is used in water treatment processes, for purifying wastewater and treating sewage.

Fun Facts about Dioxygen

  1. 21 % of the earth’s atmosphere is made up of oxygen gas.

  2. Warm water holds less dissolved oxygen than cold water because molecules are moving faster in warm water than cold water which allows oxygen to escape from the water. 

  3. The liver consumes the highest oxygen in the human body. 

  4. The health level of the water is measured by its oxygen gas content.

  5. Pure oxygen is toxic. We can’t inhale 100 % Oxygen gas. In reality, we inhale air which is 21% oxygen. 

  6. The mass of the sun is made up of around 1% Oxygen. 

  7. Oxygen is essential for our respiratory system, whereas its allotrope ozone (O3) is highly toxic. 

FAQ (Frequently Asked Questions)

  1. Write down the Reaction of Oxygen with Carbon, Hydrogen, Nitrogen, and Ammonia? 

  1. Reaction with Nitrogen - Oxygen reacts with Nitrogen to form Nitrogen Dioxide at high temperatures. Firstly both react to form Nitric Oxide. Later on, nitric oxide further reacts with oxygen to form nitrogen dioxide. 

                                                                                            N2 + O2 ⟶ NO

NO + O2 ⟶ NO2

  1. Reaction with Hydrogen - Oxygen when heated with hydrogen forms water. 

2H2 + O2 → 2H2O

  1. Reaction with Ammonia - Oxygen reacts with ammonia to form nitric oxide and water. It is the reaction involved in Ostwald’s process for the manufacturing of Nitric acid.  


  1. Reaction with Carbon - Carbon when reacted with limited oxygen gives carbon monoxide, whereas with the excess supply of oxygen forms carbon dioxide

2C + O2 → 2CO

C + O2 → CO2

2. Does Oxygen react with Alkali Metals? 

Ans. Oxygen is highly reactive with the Alkali metals(Group I elements). Alkali metals

should be kept away from the oxygen in order to prevent getting oxidized. Metals

present in the bottom of the group are more reactive than the top. 

With Lithium-    Oxygen reacts with Lithium to form Lithium Oxide.

                                                      4Li + O2 → 2Li2O  

With Sodium -   Oxygen reacts with Sodium to form oxide and Peroxide.     

                                                       4Na + O2 → 2Na2O    

                                                       2Na + O2 → Na2O2    

With Potassium -  Oxygen reacts with Potassium to form peroxide and superoxide.   

                                                         2K + O2 → 2K2O2    

                                                          K + O2 → KO2        

With Rubidium and Caesium - Both react to produce superoxides.

                                                         Rb + O2 → RbO2