Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Oxygen
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Oxygen
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Subject: Chemistry
Class: Senior Secondary 2
Term: 1st Term
Week: 2
Theme: Chemistry And Environment
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Explain the general properties of oxygen group in the periodic table write and draw the electronic structure of oxygenand explain its bonding capacity describe the laboratory and in dustrial methods for the preparation of oxygen state the physicals and chemical properties of oxygen List the compounds of oxygen explain oxidation as addition of oxygen and give examples of such reactions state the uses of oxygen
Oxygen belongs to Group 16 of the periodic table, often called the Chalcogens.
The elements in this group are: Oxygen (O) Sulphur (S) Selenium (Se) Tellurium (Te) Polonium (Po)
General Properties of Chalcogens: Electronic Configuration: All elements in this group have six valence electrons (ns2np4). This configuration makes them tend to gain two electrons to achieve a stable octet, forming 2- ions (e.g., O2−, S2−).
Valency: Primarily display a valency of
2. Higher valencies are observed for elements below oxygen due to the availability of d-orbitals.
Non-metallic Character: Oxygen and Sulphur are distinctly non-metallic. Selenium and Tellurium show metalloid characteristics, while Polonium is a radioactive metal. Non-metallic character decreases down the group.
Electronegativity: High electronegativity, decreasing down the group. Oxygen is the second most electronegative element after Fluorine.
Physical State: Oxygen is a gas, while Sulphur and others are solids at room temperature.
Occurrence: Oxygen occurs freely as a diatomic gas (O2) and combined in water, minerals, and organic compounds. Sulphur occurs freely and in sulphides/sulphates.
Atomic Number: 8 Electronic Configuration: 1s22s22p4 or 2, 6 (K-shell: 2 electrons, L-shell: 6 electrons).
Valence Electrons: 6 Lewis Dot Structure: Represented with 6 dots around the 'O' symbol. ``` . . : O : . . ``` Bonding Capacity: Oxygen typically forms two chemical bonds to achieve a stable octet configuration.
Covalent Bonding: Most common. It shares two electrons with another atom (e.g., in H2O, CO2). In its elemental form (O2), two oxygen atoms share two pairs of electrons forming a double covalent bond (O=O).
Ionic Bonding: Can gain two electrons from highly electropositive metals (e.g., Na2O, CaO) to form the oxide ion (O2−). Oxygen can be prepared in the laboratory by the thermal decomposition of certain oxygen-containing compounds or the catalytic decomposition of hydrogen peroxide.
Method 1: Catalytic Decomposition of Hydrogen Peroxide (H2O2)
Principle: Hydrogen peroxide readily decomposes to water and oxygen, but the reaction is slow at room temperature. A catalyst like manganese(IV) oxide (MnO2) speeds up the decomposition.
Equation: 2H2O2(aq) $\xrightarrow{\text{MnO2}}$ 2H2O(l) + O2(g)
Procedure: Set up a delivery tube and gas jar/trough for downward displacement of water (or upward delivery of air). Place a small amount of manganese(IV) oxide (MnO2) into a flat-bottomed flask. Add dilute hydrogen peroxide solution drop by drop through a thistle funnel. Oxygen gas is evolved rapidly and collected.
Diagram (for teacher's reference): (Imagine a standard lab setup: flat-bottomed flask, thistle funnel, delivery tube, gas jar inverted in a trough of water).
Role of MnO2: Acts as a catalyst. It increases the rate of reaction without being consumed itself.
Method 2: Thermal Decomposition of Potassium Chlorate(V) (KClO3)
Principle: Potassium chlorate decomposes on heating to produce potassium chloride and oxygen. The reaction is slower and requires higher temperatures without a catalyst. MnO2 is often added as a catalyst to lower the decomposition temperature and increase the rate.
Equation: 2KClO3(s) $\xrightarrow{\text{MnO2 / Heat}}$ 2KCl(s) + 3O2(g)
Procedure: Mix potassium chlorate and manganese(IV) oxide thoroughly in a 3:1 ratio (by mass) in a hard glass test tube. Heat the mixture gently at first, then more strongly. Oxygen gas is evolved and collected. Safety
Note: This method requires careful heating as KClO3 is a strong oxidizer.
Method 3: Thermal Decomposition of Potassium Permanganate (KMnO4)
Principle: Potassium permanganate decomposes on heating to yield potassium manganate, manganese(IV) oxide, and oxygen.
Equation: 2KMnO4(s) $\xrightarrow{\text{Heat}}$ K2MnO4(s) + MnO2(s) + O2(g)
Procedure: Place potassium permanganate in a hard glass test tube. Heat gently. Oxygen gas is evolved and collected.
Method of Collection: Downward displacement of water: Most common method because oxygen is only sparingly soluble in water.
Upward delivery of air: Can also be used because oxygen is slightly denser than air (molecular weight of O2 = 32 g/mol, average molecular weight of air ≈ 29 g/mol). This is the most common and economical method for large-scale production of oxygen, nitrogen, and argon.
Principle: Air is a mixture of gases with different boiling points. By liquefying air and then gradually warming it, the components can be separated based on their distinct boiling points.
Nitrogen (N2): Boiling point = -196 °C Oxygen (O2): Boiling point = -183 °C Argon (Ar): Boiling point = -186 °C Steps: Purification/Filtration: Air is first filtered to remove dust particles and impurities.
Compression: The purified air is then compressed to a high pressure (around 200 atmospheres).
Cooling: The compressed air is cooled to very low temperatures (below -200°C) using a series of heat exchangers and an expansion turbine (Joule-Thomson effect). This causes the air to liquefy.
Removal of CO2 and Water Vapour: Carbon dioxide and water vapour freeze out at these low temperatures and are removed by adsorption or freezing to prevent blockage of pipes.
Fractional Distillation: The liquid air (primarily liquid nitrogen and oxygen) is fed into a tall fractional distillation column. As the liquid air slowly warms up, nitrogen (with a lower boiling point of -196°C) boils off first as a gas and is collected at the top of the column. Argon (b.p. -186°C) collects in a middle section. Oxygen (with a higher boiling point of -183°C) remains as a liquid at the bottom of the column and is collected.
Alternative Industrial Method: Electrolysis of Water Principle: When an electric current is passed through acidified water, it decomposes into hydrogen and oxygen gases.
Equation: 2H2O(l) $\xrightarrow{\text{Electrolysis}}$ 2H2(g) + O2(g)
Note: This method is more expensive due to the high electricity consumption and is typically used when high-purity hydrogen is also required.
Healthcare and Emergency Services: In Nigeria, oxygen is critical in hospitals for supporting patients with respiratory illnesses (e.g., pneumonia, asthma, tuberculosis, and previously, severe COVID-19 cases). Oxygen cylinders are vital for ambulance services, operating theatres, and intensive care units in cities like Abuja, Kano, and Enugu. Understanding the properties and production of oxygen directly relates to its life-saving applications. Industrial Development and Economic Impact: The fractional distillation of liquid air is a cornerstone for producing bulk industrial gases. In Nigeria, companies that produce oxygen, nitrogen, and argon gases serve various sectors. For example, oxygen is crucial for welding and metal fabrication workshops (e.g., foundries in Aba, Nnewi, or Lagos), steel production (Ajaokuta Steel Company), and cement manufacturing (e.g., Dangote Cement plants) for high-temperature kilns. Students can relate to local artisans using welding equipment. Environmental Management and Water Treatment: Oxygen plays a vital role in aerobic wastewater treatment plants, which are becoming more common in Nigerian cities to manage sewage and industrial effluents. By introducing oxygen, microorganisms are encouraged to break down organic pollutants more efficiently, preventing water pollution in rivers and streams, and ensuring cleaner water sources for communities, which is a significant environmental challenge in rapidly urbanizing areas. This connects to public health and sustainable development.