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There are certain elements which are essential to sustain life on earth like water or sunlight. Among them, Oxygen happens to be the most essential element. Without it, absolutely no form of life can exist. When two atoms of oxygen combine, they form Dioxygen, a highly reactive non-metal. It is more commonly know as the oxygen we breathe in.
Read Also: Electronic Configuration of Group 16 Elements
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Key Terms: Oxygen, Group 15 Elements, Phosphine, atoms, chemical compound, Boiling Point
What is Dioxygen?
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Dioxygen is an allotrope of oxygen that exists in the form of a gas. To reiterate, it is the most essential element in the living world. It is a P-block element that comes under the group 16 of the periodic table.
Chemical formula : O2
Two atoms of oxygen combine to form Dioxygen.
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Preparation of Dioxygen
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Oxygen can be derived from several means:
In Laboratories
Laboratory preparation of Dioxygen is carried out when potassium chloride is heated with magnesium chloride as a catalyst.
2KClO3 → 2KCl + 3O2
From Ores Reduction
2Ag2O → 4Ag + O2
2Fe3O2 → 4Fe + 3O2
Iron Oxide converts to Iron and Dioxygen
From Hydrogen peroxide
Hydrogen peroxide is very unstable in the presence of heat and sunlight.
2H2O2 → 2H2O + O2
Read More: Oxiacids of Sulphur
Commercial Preparation
The commercial preparation of dioxygen is carried out through certain measures:
From Air: Atmospheric Pressure which contains 78% of nitrogen and 21% of oxygen with other elements is collected and filtered and is passed through high pressure and low temperature
(78 K i.e. the boiling point of nitrogen) which causes liquidation of nitrogen and both nitrogen and oxygen are separated. This process is called the Distillation process.
Distillation process
Read More: Manufacturing of Sulfuric acid through contact process
Through Electrolysis of Water: This method is carried out with the help of two electrodes one is cathode and other anode is placed in the water each connected to water, when high voltage current is passed through the water H+ ions and OH- ions gets separated and attracts to the rode as cathode is negatively charged due to cation and anode is positively charged due to anion.
Electrolysis of Water
Read More: Specific Heat of water
Properties of Dioxygen
- Dioxygen does not have any odour, colour or taste.
- It is soluble in water that helps in sustenance of aquatic life.
- The boiling point of oxygen is 90.2 K and Melting Point is around 50.36 K.
- It is heavier than air with a density of 1.429 g/L.
- It is present in all three forms solid, liquid and gas according to the atmospheric temperature and pressure.
- It is the most electronegative element after fluorine.
- It reacts with all metals and non-metals.
- It is a paramagnetic element even though it has an even number of electrons.
Read More: Organometallic Compounds
Uses of Dioxygen
- It is essential for the respiration process and oxygen supplements in the medical field.
- Flames of Oxy- Acetylene and Oxy- Hydrogen are highly used in laser cutting and welding purposes.
- It is abundantly used in metallurgy processes.
- Liquid form of oxygen is used as Rocket fuel.
- It is used in melting iron to form steel.
- It is also used in the production of nitric acid.
Read More: Uses of Sulphur Dioxide
Things to Remember
- Dioxygen is an allotrope of oxygen that exists in the form of a gas.
- It is a P-block element that comes under the group 16 of the periodic table.
- The chemical formula for Dioxygen is O2
- Laboratory preparation of Dioxygen is carried out when potassium chloride is heated with magnesium chloride as a catalyst.
- The boiling point of oxygen is 90.2 K and melting point is around 50.36 K.
- It is the most electronegative element after fluorine and reacts with all metals and non metals.
- Dioxygen is essential for the respiration process and oxygen supplements in the medical field.
Sample Questions
Ques. (a) Complete the following chemical equations :
(i) Cu + HNO3 (dilute) →
(ii) P4 + NaOH + H2O →
(b) (i) Why does R3P = O exist but R3N = O does not? (R = alkyl group)
(ii) Why is dioxygen a gas but sulphur a solid?
(iii) Why are halogens coloured? (Comptt. Delhi 2015)
Ans. (a)
b) (i) Nitrogen in R3N = O cannot form pπ – dπ multiple bonds because it cannot expand its covalency beyond 4 due to absence of d-orbital, so it will not exist. But R3P = O can do so due to presence of d-orbitals and formation of pπ – dπ multiple bonds which can expand its covalency up to 5.
(ii) Because of bigger size and the strong forces of attraction holding 8 atoms, their bonds cannot be broken easily and hence sulphur exists as solid while oxygen due to high electro-negativity and tendency to form pπ – dπ multiple bonds through Vander-waals forces of attraction can be broken easily and hence exists as gas.
(iii) All halogens are coloured due to absorption of light in the visible region as a result of which their electrons get excited to higher energy levels and while returning to lower level transmit energy of corresponding colour.
Ques. (a) What happens when :
(i) HCl reacts with finely powdered iron.
(ii) Cl3 reacts with hot concentrated solution of NaOH.
(b) Give appropriate reason for each of the following :
(i) Sulphur vapour exhibits some paramagnetic character.
(ii) NH3 is more basic than PH3
(iii) Dioxygen is a gas but sulphur a solid. (Comptt. Delhi 2016)
Ans. (a) (i) It forms FeCl2 and H2 gas
(b) (i) Sulphur above 1000 K exists partially as S2 molecule which has two unpaired
electrons in its Anti Bonding orbitals.
(ii) Due to small size of N, NH3 molecule has small surface area and high electron density in comparison to PH3. Hence it can donate lone pair of electron more readily.
(iii) In dioxygen there is Pπ – Pπ multiple bonding and no cation hence it is a gas.
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