Key Reactions and Everyday Applications of Dioxygen
Dioxygen, one of the common allotropes 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, 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.
Laboratory Preparation of Dioxygen
There are numerous ways of preparing dioxygen in the laboratory.
Catalytic decomposition of Sodium Potassium Chlorate with Magnesium dioxide as the catalytic produces dioxygen.
\[ 2KClO_{3} \rightarrow 2KCl + 3O_{2} \]
This reaction occurs on heating, in the presence of MnO2 at 420K.
Thermal decomposition of metal oxides with relatively low electrode potential in the electrochemical series like that of Mercury and Silver oxides etc. produces Dioxygen.
\[2HgO (s) \rightarrow 2Hg (l) + O_{2} (g)\]
\[ 2PbO_{2} (s) \rightarrow 2PbO (s) + O_{2} (g) \]
Salts rich in oxygen, like nitrates and permanganates, produce Dioxygen when decomposed thermally.
\[ 2KNO_{3} \rightarrow 2KNO_{2} + O_{2} \]
\[ 2KMnO_{4} \rightarrow K_{2}MnO_{4} + MnO_{2} + O_{2} \]
\[2NaNO_{3} \rightarrow 2NaNO_{2} + O_{2} \]
The decomposition of Hydrogen Peroxide also produces oxygen and to increase the rate of decomposition, manganese(IV) oxide is added as a catalyst.
\[2H_{2}O_{2}(aq) \rightarrow 2H_{2}O(l) + O_{2} (g)\]
Industrial Production of Oxygen
There are two primary methods used for the industrial production of O2 from the air.
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.
Another method includes passing 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.
Physical Properties of Dioxygen
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.
\[4Na + O_{2} \rightarrow 2Na_{2}O \](With Metal)
\[C + O_{2} \rightarrow CO_{2} \](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.
\[Fuel + O_{2} \rightarrow CO_{2} + H_{2}O\]
Example, CH4 + O2 ⟶ CO2 + H2O
Oxygen, along with moisture, is responsible for the formation of rust on the iron.
\[Fe + O_{2}+ H_{2}O ⟶ Fe_{2}O_{3}n.H_{2}O \](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
21 % of the earth’s atmosphere is made up of oxygen gas.
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.
The liver consumes the highest oxygen in the human body.
The health level of the water is measured by its oxygen gas content.
Pure oxygen is toxic. We can’t inhale 100 % Oxygen gas. In reality, we inhale air which is 21% oxygen.
The mass of the sun is made up of around 1% Oxygen.
Oxygen is essential for our respiratory system, whereas its allotrope ozone (O3) is highly toxic.
Conclusion
In the above-given information, Vedantu’s expert team has described Dioxygen - Preparation, Properties, and Uses which are to be studied by the students to provide and get the best result in the examination. Candidates appearing for chemistry examination should know that Dioxygen is an important chapter that has a good weightage and question based on this topic can be of any type multiple choice question, very short answer question, short answer question or long answers question, therefore students should prepare accordingly so that they are able to write answers properly and get prepared for the examination.
To study this chapter properly students should cover everything about these like dioxygen -preparation, properties and uses. Candidates can get involved in the studies with the help of Vedantu’s experts and get a better understanding of all the topics. Candidates should also study the important questions and the sample papers to get ready for the examination. Chemistry needs learning of the formulas so students can prepare revision notes for all the formulas and study thoroughly to get a command in the formulas of Chemistry.
FAQs on Dioxygen: Preparation, Properties, and Uses Explained
1. What are the primary methods for preparing dioxygen in a laboratory setting as per the CBSE syllabus?
As per the CBSE 2025-26 syllabus, there are three primary laboratory methods for preparing dioxygen (O₂):
By heating oxygen-containing salts: Compounds like chlorates, nitrates, and permanganates decompose on heating to release dioxygen. For example, heating potassium chlorate (KClO₃) in the presence of manganese dioxide (MnO₂) as a catalyst yields O₂.2KClO₃(s) → 2KCl(s) + 3O₂(g)
By thermal decomposition of oxides: Oxides of metals that are low in the electrochemical series (like Ag, Hg, Pb) decompose upon heating. For instance, silver oxide (Ag₂O) breaks down into silver and dioxygen.2Ag₂O(s) → 4Ag(s) + O₂(g)
By decomposition of hydrogen peroxide: Hydrogen peroxide (H₂O₂) readily decomposes into water and dioxygen, a reaction catalysed by finely divided metals or manganese dioxide.2H₂O₂(aq) → 2H₂O(l) + O₂(g)
2. How is dioxygen produced on a large, industrial scale?
On an industrial scale, dioxygen is primarily produced by the fractional distillation of liquefied air. Air is first liquefied by compressing and cooling it. Then, the liquid air is allowed to warm up slowly in a fractional distillation column. Since liquid nitrogen has a lower boiling point (-196 °C) than liquid oxygen (-183 °C), nitrogen vaporises first, leaving behind almost pure liquid dioxygen. Another method involves the electrolysis of water, which produces highly pure hydrogen and oxygen, but this is more expensive and used when high-purity hydrogen is also required.
3. What are the key physical and chemical properties of dioxygen?
Dioxygen (O₂) has distinct physical and chemical properties crucial for understanding its behaviour.
Physical Properties: It is a colourless, odourless, and tasteless gas. It is sparingly soluble in water, which is essential for aquatic life. It liquefies at 90 K and freezes at 55 K. One of its most interesting properties is that it is paramagnetic, meaning it is weakly attracted to magnetic fields.
Chemical Properties: Dioxygen is highly reactive and directly reacts with nearly all metals and non-metals, except for noble gases and noble metals like gold and platinum. These reactions are often strongly exothermic and are called combustion reactions. It acts as a powerful oxidising agent.
4. What is the fundamental difference between atomic oxygen (O) and dioxygen (O₂)?
The fundamental difference lies in their structure and stability. Atomic oxygen (O) is a single, highly reactive oxygen atom with an unstable electron configuration. It is a free radical and cannot exist independently for long under normal conditions. In contrast, dioxygen (O₂) is a molecule composed of two oxygen atoms joined by a double covalent bond. This molecular form is the stable, common state of oxygen found in Earth's atmosphere and is essential for respiration.
5. Why is dioxygen (O₂) a gas at room temperature, while sulfur (S₈), in the same group, is a solid?
This difference arises from the nature of bonding and molecular size. Oxygen, being a small atom, can form strong pπ-pπ multiple bonds with another oxygen atom, resulting in a stable, discrete O₂ molecule. The forces between these small O₂ molecules (van der Waals forces) are very weak, making it a gas. Sulfur, being larger, cannot form stable pπ-pπ bonds. Instead, it forms strong single bonds with other sulfur atoms, creating a puckered, eight-membered ring structure (S₈). These large S₈ molecules have much stronger intermolecular van der Waals forces, which hold them together as a solid at room temperature.
6. How is the paramagnetic nature of dioxygen explained by Molecular Orbital Theory (MOT)?
While Valence Bond Theory fails to explain its magnetic behaviour, Molecular Orbital Theory (MOT) provides a clear explanation. When the molecular orbital diagram for O₂ is constructed, the last two electrons enter the π* (pi-antibonding) molecular orbitals. According to Hund's rule, these two electrons occupy two different π* orbitals, each with a parallel spin (unpaired). The presence of these two unpaired electrons is the reason why dioxygen is paramagnetic.
7. How does dioxygen react with metals and non-metals to form different types of oxides?
Dioxygen's reaction with other elements forms oxides, which can be classified based on their acidic or basic nature.
Reaction with Metals: It reacts with most metals to form basic oxides (e.g., 2Ca + O₂ → 2CaO). Highly reactive alkali metals can also form peroxides (e.g., 2Na + O₂ → Na₂O₂) and superoxides (e.g., K + O₂ → KO₂).
Reaction with Non-metals: It reacts with non-metals to form acidic oxides (e.g., C + O₂ → CO₂; S + O₂ → SO₂).
Amphoteric Oxides: Some elements, like aluminium, react with dioxygen to form amphoteric oxides, which exhibit both acidic and basic properties (e.g., 4Al + 3O₂ → 2Al₂O₃).
8. What are the most significant uses of dioxygen in industry and daily life?
Dioxygen is indispensable for both biological and industrial processes.
Respiration: Its primary use is in cellular respiration for all aerobic life to produce energy.
Medical Use: It is used in hospitals for patients with breathing difficulties and during anaesthesia.
Industrial Combustion: It is used in manufacturing steel (oxy-steel process) and in oxy-acetylene torches for welding and cutting metals, as it produces extremely high temperatures.
Rocket Fuel: Liquid oxygen is used as a powerful oxidizer in rocket propulsion systems.
Chemical Synthesis: It is used in the synthesis of many chemicals, including nitric acid and sulfuric acid.
