Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Iron
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Iron
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Subject: Chemistry
Class: Senior Secondary 3
Term: 1st Term
Week: 4
Theme: Chemistry And Industry
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state the relativeabundance of iron ore in nature state the physical and chemical properties of iron describe the processfor extraction of iron from its ore state the causes of rusting in iron suggest ways of preventing rusting of iron
Materials: Pictures of iron ore, blast furnace diagram, samples of iron objects (new and rusted), galvanized iron, stainless steel, painted iron, small iron nails, water, boiled water (cooled), salt solution, cooking oil, test tubes, test tube rack.
Teacher Activities: Introduction (10 minutes): Begin by displaying various iron objects (e.g., a cutlass, a rusted nail, a car part, a stainless steel spoon, a galvanized roofing sheet).
Engage students with questions: "What are these objects made of?" "Why do some look shiny and others reddish-brown?" "Where do we get the raw material for these?" Introduce the topic "Iron" and its relevance to everyday life and industries in Nigeria (e.g., construction, agriculture, transport). State the learning objectives for the lesson in student-friendly terms.
Relative Abundance of Iron (10 minutes): Explain that iron is very abundant in the Earth's crust. Show pictures of common iron ores, especially haematite, and mention its presence in Nigeria (e.g., Itakpe). Discuss that iron rarely occurs free due to its reactivity. Physical and Chemical Properties of Iron (20 minutes): Physical: Use the displayed iron objects to discuss properties like appearance, magnetism (demonstrate with a magnet), and density (briefly explain its heaviness). Discuss malleability and ductility, relating it to the ability to make various tools or sheets.
Chemical: Reaction with Air/Oxygen (Rusting): Introduce rusting as a key chemical property. Explain the conditions necessary (oxygen and water).
Reaction with Acids/Steam: Briefly explain these reactions, writing the balanced chemical equations on the board. Emphasize the formation of iron(II) salts with dilute acids and the passivation effect of conc. HNO
3. Extraction of Iron (30 minutes): Display a large diagram of a blast furnace. Explain the raw materials (iron ore, coke, limestone) and their roles. Guide students through the step-by-step process of iron extraction, starting from the top of the furnace. Write and explain the key chemical equations for: Combustion of coke: $C + O_2 \rightarrow CO_2$ Formation of reducing agent: $CO_2 + C \rightarrow 2CO$ Reduction of iron ore: $Fe_2O_3 \rightarrow Fe_3O_4 \rightarrow FeO \rightarrow Fe$ (emphasize the role of CO).
Slag formation: $CaCO_3 \rightarrow CaO + CO_2$, then $CaO + SiO_2 \rightarrow CaSiO_3$. Explain the collection of molten iron (pig iron) and slag.
Causes of Rusting (20 minutes): Revisit the concept of rusting introduced earlier. Conduct a simple demonstration (or set up prior to class for observation): Set up three test tubes: Nail in tap water (exposed to air). Nail in boiled water with a layer of oil (removes dissolved air, oil prevents air re-entry). Nail in tap water with a few crystals of salt (electrolyte). Have students observe and predict which nail will rust fastest/slowest. Explain the electrochemical nature of rusting and the roles of oxygen and water. Discuss factors that accelerate rusting (electrolytes, acids, impurities).
Ways of Preventing Rusting (20 minutes): Initiate a brainstorming session: "How do we protect metal objects at home or in our community from rusting?" Discuss each method in detail: Painting/Greasing/Oiling: Show examples.
Galvanizing: Show a galvanized sheet, explain sacrificial protection.
Electroplating: Show plated items, discuss tin cans.
Sacrificial Protection: Explain its application for large structures.
Alloying: Show stainless steel and explain its resistance.
Other methods: Blueing, dry storage. Emphasize the practical application of these methods in Nigerian context.
Student Activities: Question & Answer: Actively participate in discussions, answer questions posed by the teacher.
Observation: Observe the demonstration/experiment on rusting conditions and record observations.
Note-Taking: Take detailed notes on key concepts, properties, reactions, and processes.
Group Discussion: In groups, discuss the roles of each raw material in the blast furnace or brainstorm methods of rust prevention.
Drawing: Draw a simplified diagram of a blast furnace, labelling key parts and indicating material flow. Real-Life
Examples: Identify and share examples of iron objects, rusting, and rust prevention methods observed in their daily lives. The teacher should guide students through these questions, providing support and clarifications.
Question 1: Name the most important iron ore found in Nigeria and write its chemical formula.
Solution: The most important iron ore found in Nigeria is Haematite. Its chemical formula is Fe2O
3. Commentary: This assesses the student's knowledge of the primary iron ore and its chemical representation, directly linking to the Nigerian context.
Question 2: State three physical properties and two chemical properties of pure iron.
Solution: Physical Properties: Lustrous, silvery-white appearance (when pure). High melting point (1538 °C). Good conductor of heat and electricity. Ferromagnetic (strongly attracted to magnets). Malleable and ductile. (Any three of the above or other valid physical properties)
Chemical Properties: Reacts with oxygen and water to form rust (hydrated iron(III) oxide). Reacts with dilute acids (e.g., HCl) to produce iron(II) salts and hydrogen gas. Reacts with steam at high temperatures to form iron(II,III) oxide and hydrogen. Forms iron(III) halides with halogens (e.g., chlorine) when heated. Concentrated nitric acid passivates iron. (Any two of the above or other valid chemical properties)
Commentary: This question checks the understanding of both categories of properties, emphasizing the distinction.
Question 3: Describe the role of carbon monoxide (CO) in the extraction of iron in the blast furnace. Write the relevant chemical equation for its main reducing action.
Solution: Carbon monoxide (CO) acts as the primary reducing agent in the blast furnace. It removes oxygen from the iron ore, converting the iron oxides back to metallic iron. The main reducing action occurs when carbon monoxide reduces iron(II) oxide (FeO) to molten iron: $FeO(s) + CO(g) \rightarrow Fe(l) + CO_2(g)$
Commentary: This targets a crucial understanding of the chemical reactions and the function of one of the raw materials in the blast furnace.
Question 4: Explain why an iron nail would rust faster in seawater than in tap water.
Solution: An iron nail rusts faster in seawater because seawater contains dissolved salts (e.g., sodium chloride), which act as electrolytes. Electrolytes increase the electrical conductivity of the water. In the electrochemical process of rusting, increased conductivity facilitates the flow of electrons and ions, thereby accelerating the overall oxidation-reduction reactions involved in rust formation. Tap water, having fewer dissolved salts, is a poorer electrolyte, leading to slower rusting.
Commentary: This question tests the understanding of factors influencing rusting rate, connecting it to a common real-life scenario in coastal areas of Nigeria.
Question 5: Suggest two practical methods commonly used in Nigeria to prevent a newly fabricated iron gate from rusting and briefly explain how each method works.
Solution: Painting: The iron gate can be coated with a layer of paint. The paint forms a physical barrier on the surface of the iron, preventing direct contact of the iron with both oxygen from the air and moisture (water). This physical isolation stops the electrochemical process of rusting.
Galvanizing: The iron gate can be galvanized, which means it is coated with a layer of zinc. Zinc is more reactive than iron. If the zinc coating is scratched, the zinc will corrode preferentially (sacrificial protection) instead of the iron, thereby protecting the iron gate from rusting. (Other valid answers include alloying (stainless steel gates), electroplating with chromium/nickel.)
Commentary: This question applies the knowledge of rust prevention methods to a specific, common Nigerian context (iron gates), requiring both method identification and explanation. Iron is the second most abundant metal in the Earth's crust (after aluminium) and the fourth most abundant element overall. It rarely occurs as a free metal due to its reactivity, but is found extensively in the form of ores.
Common Iron Ores: Haematite (or Hematite): Fe2O3 (Iron(III) oxide). This is the most important and common ore globally, and the primary iron ore found in significant deposits in Nigeria (e.g., Itakpe in Kogi State). It has a reddish-brown colour.
Magnetite: Fe3O4 (Iron(II,III) oxide). This ore is strongly magnetic and typically black.
Limonite: Fe2O3.nH2O (Hydrated iron(III) oxide). This is essentially rust, yellowish-brown in colour.
Siderite: FeCO3 (Iron(II) carbonate). A greyish-white ore.
Iron Pyrites: FeS2 (Iron(II) disulfide). Often called "Fool's Gold" due to its metallic luster. It is generally not used for iron extraction due to the difficulty of removing sulfur and the environmental concerns of sulfur dioxide production.
I. Physical Properties: Appearance: Pure iron is a lustrous, silvery-white metal.
However, it quickly tarnishes to a greyish colour on exposure to air due to the formation of a thin oxide layer.
State at Room Temperature: Solid.
Melting Point: Relatively high at 1538 °
C. Boiling Point: Very high at 2862 °
C. Density: High, 7.87 g/cm
3. Hardness: Moderately hard. Its hardness can be varied by alloying with carbon to form steel.
Malleability and Ductility: It is both malleable (can be hammered into sheets) and ductile (can be drawn into wires), especially when hot.
Conductivity: Good conductor of heat and electricity.
Magnetism: It is a ferromagnetic material, meaning it is strongly attracted to magnets and can be easily magnetized (e.g., electromagnets). I
I. Chemical Properties: Reaction with Air/Oxygen: Rusting: In the presence of both oxygen and moisture (water), iron slowly oxidizes to form hydrated iron(III) oxide, commonly known as rust. This is an electrochemical process.
Simplified overall reaction: $4Fe(s) + 3O_2(g) + xH_2O(l) \rightarrow 2Fe_2O_3.xH_2O(s)$ (Rust, hydrated iron(III) oxide)
Combustion: When heated strongly in air or pure oxygen, iron burns with a bright spark, forming iron(II,III) oxide (magnetite). $3Fe(s) + 2O_2(g) \xrightarrow{heat} Fe_3O_4(s)$ Reaction with Water/Steam: Iron does not react with cold water but reacts with steam when heated to red-hot, forming iron(II,III) oxide and hydrogen gas. $3Fe(s) + 4H_2O(g) \xrightarrow{red-hot} Fe_3O_4(s) + 4H_2(g)$ Reaction with Acids: Dilute non-oxidizing acids (e.g., HCl, H2SO4): Iron reacts with dilute acids to produce iron(II) salts and hydrogen gas. $Fe(s) + 2HCl(aq) \rightarrow FeCl_2(aq) + H_2(g)$ (Iron(II) chloride) $Fe(s) + H_2SO_4(aq) \rightarrow FeSO_4(aq) + H_2(g)$ (Iron(II) sulfate)
Dilute Nitric Acid (HNO3): Reacts to form iron(III) nitrate, nitric oxide, and water. $Fe(s) + 4HNO_3(dilute) \rightarrow Fe(NO_3)_3(aq) + NO(g) + 2H_2O(l)$ Concentrated Sulphuric Acid (H2SO4): Hot, concentrated sulphuric acid oxidizes iron to iron(III) sulphate, producing sulfur dioxide gas. $2Fe(s) + 6H_2SO_4(conc) \rightarrow Fe_2(SO_4)_3(aq) + 3SO_2(g) + 6H_2O(l)$ Concentrated Nitric Acid (HNO3): Concentrated nitric acid renders iron passive. It forms a thin, protective, unreactive oxide layer on the surface of the iron, preventing further reaction. The iron becomes unreactive to dilute acids too. This effect can be removed by scratching the surface or treating with dilute HCl. Reaction with Halogens (e.g., Chlorine): When heated, iron reacts with halogens to form iron(III) halides. $2Fe(s) + 3Cl_2(g) \xrightarrow{heat} 2FeCl_3(s)$ (Iron(III) chloride)
Note: It typically forms iron(III) compounds due to the strong oxidizing nature of halogens.
Construction and Infrastructure Development: Iron, predominantly in the form of steel (an alloy of iron), is the backbone of Nigeria's construction industry. From multi-storey buildings in Abuja and Lagos to bridges (e.g., Third Mainland Bridge), railway tracks, and electricity transmission towers, steel provides strength and structural integrity. Understanding iron extraction and properties helps appreciate the material science behind these vital structures. Rusting prevention is crucial for the longevity of public infrastructure.
Agriculture and Domestic Tools: In many Nigerian communities, agricultural tools like hoes, cutlasses, plows, and domestic items like cooking pots (cast iron), gates, and window grilles are made from iron or steel. Knowledge of rusting helps in proper maintenance, such as oiling cutlasses after use, painting gates, or choosing stainless steel for kitchenware to extend their lifespan and reduce replacement costs for families and farmers.
Oil and Gas Industry/Transportation: Nigeria's vast oil and gas sector relies heavily on iron and steel for pipelines, offshore platforms, storage tanks, and refinery equipment. These structures are constantly exposed to corrosive environments (saltwater, humid air). Methods like sacrificial protection (cathodic protection) using zinc or magnesium anodes are vital for preventing corrosion of these critical assets, ensuring safety and economic stability. Similarly, vehicles (cars, trucks, motorcycles) are largely built with steel, and rusting prevention techniques like painting and electroplating are essential for their durability.
Local Manufacturing and Artisanship: Small-scale industries and local blacksmiths in Nigeria utilize iron to fabricate gates, security doors, window frames, furniture, and custom tools. Understanding the properties of iron and methods of working with it (e.g., heating to make it malleable) is fundamental to their craft. Knowledge of rust prevention allows them to produce higher quality, more durable products for their customers.