5.2. Using the reactivity series and displacement reactions

• Metals have electrons in the outermost shell that they want to get rid of when they react with other substances
• Reactivity of a metal refers to how easily it forms positive ions by getting rid of outer shell electrons
• The reactivity series arranges metals in order of their reactivity, with the most reactive metals forming ions most easily
• Group 1 metals are the most reactive, followed by group 2 metals, and then the transition metals which are generally the least reactive
• When metals react with acids, they form a salt and hydrogen gas
• Potassium reacts explosively with hydrochloric acid, producing potassium chloride and hydrogen
• Reactions become less violent as we go down the series, with magnesium producing bubbles and copper usually not reacting at all
• The temperature change of reactions can also indicate the reactivity of metals, with the most reactive metals producing the most heat
• In displacement reactions, more reactive metals can displace less reactive ones
• For example, magnesium can displace iron in a solution of iron sulfate to form magnesium sulfate and iron
• Less reactive metals like copper cannot displace more reactive metals like iron
• When metals react with water, they form metal hydroxides and hydrogen
• Only the most reactive metals can react with water, while metals like zinc, iron, and copper won't react at all or only slightly
• To ensure a fair test when comparing metals, it's important to use metal samples with the same mass and surface area, as well as the same type and concentration of acid
• The reactivity series is used to predict which metal will displace another from its compound
• A more reactive metal can be identified by looking at where it appears on the reactivity series.
• Metal A (more reactive) will displace Metal B (less reactive) from its salt solution.
• In a reaction between a metal and an acid, the metal loses electrons to become positively charged ions called cations.
• In a reaction between a metal and an acid, the metal that forms a more stable ion will react faster than one that forms a less stable ion.
• "Molten" refers to a substance that has been heated to the point where it melts and becomes a liquid. When a solid substance reaches its melting point, the intermolecular forces holding its particles together weaken, allowing the particles to move freely, resulting in the substance transitioning from a solid to a liquid state. For example, when ice (solid water) is heated to its melting point, it becomes molten water.
• "Ores" are naturally occurring rocks or minerals from which metals or other valuable substances can be extracted economically. Ores typically contain high concentrations of the desired material, making them valuable sources for extraction and processing. Common examples of ores include bauxite, which is the primary source of aluminum, and hematite, which is a major source of iron. Ores are usually mined from the earth's crust and processed to extract the valuable components, which may include metals, minerals, or other materials.
• Displacement reactions, such as the thermite reaction described here, are commonly used in various industries for their ability to produce specific metals or compounds through chemical reactions. In the case of the thermite reaction between aluminium and iron oxide, it is particularly useful for welding applications, as illustrated in the example of welding railway rails together.
• Welding Applications: The thermite reaction is utilized to weld railway rails together, a process known as thermit welding. Railway tracks need to be joined securely to ensure smooth and safe passage of trains. Traditional welding methods may not be feasible in all situations, especially when working in remote areas or directly on railway lines. The thermite reaction offers a solution by providing a simple and effective method for joining rails together
• Thermit Reaction: The thermite reaction involves the reduction of iron oxide (Fe2O3) by aluminium (Al) to produce iron (Fe) and aluminium oxide (Al2O3). This highly exothermic reaction generates a significant amount of heat, with temperatures reaching well above the melting point of iron. The molten iron produced serves as a welding material that fuses the rails together.
• Energy Source: To initiate the thermite reaction, an ignition source is required. In the described process, magnesium powder and barium nitrate are used in a separate exothermic reaction to provide the necessary heat to start the thermite reaction. The ignition reaction releases energy, which ignites the mixture of aluminium and iron oxide, initiating the displacement reaction.
• Advantages: The thermite welding process offers several advantages for industrial applications:

  • It does not require complex equipment, making it suitable for on-site welding.
  • The reaction produces a high temperature, allowing for the welding of large metal structures.
  • It creates a strong and durable bond between metal surfaces, ensuring structural integrity.
• The thermite reaction is a type of redox reaction that occurs when aluminium reacts with iron(III) oxide to form pure iron and aluminium oxide. The reaction is highly exothermic, meaning it releases a large amount of energy in the form of heat. This makes it ideal for use in welding applications, as the generated heat allows the molten iron to flow into the gap between the rails being joined.
• Advantages of Thermit Welding: One advantage of using the thermite reaction for rail welding is that it does not require any external power supply, making it suitable for use in remote locations without access to electricity. Additionally, the reaction produces very little smoke or fumes, reducing environmental pollution compared to traditional welding techniques.
• Displacement using carbon, particularly in the extraction of metals from their ores, is a fundamental process in metallurgy. While carbon itself is not a metal, its ability to displace certain metals from their compounds is exploited in various industrial processes. Here's how displacement using carbon works, focusing on its application in extracting metals like iron, zinc, tin, and lead from their ores:
• Principle of Displacement: Carbon, in the form of charcoal or coke (a processed form of coal), can displace certain metals from their ores when heated at high temperatures. This displacement occurs because carbon is more reactive than the metals it displaces. When carbon reacts with metal compounds present in ores, it forms metal and carbon dioxide.
• Historical Context: The use of carbon for displacing metals from their ores dates back thousands of years. Ancient civilizations, such as the Egyptians, Greeks, and Romans, discovered the process of extracting metals like iron using charcoal (a type of carbon) in primitive furnaces. This marked the beginning of metallurgical practices that laid the foundation for modern industrial processes.
• Modern Applications: Today, displacement reactions using carbon are still widely employed in industrial settings, especially in the production of metals on a large scale. Blast furnaces, commonly used in the steel industry, are prime examples of facilities where carbon is utilized to extract iron from iron ores, primarily iron oxide (Fe2O3 or Fe3O4).
• Blast Furnace Process: In a blast furnace, iron ore (iron oxide) is combined with coke (carbon) and limestone (calcium carbonate) and heated to extremely high temperatures. The carbon in coke acts as a reducing agent, reacting with the iron oxide to produce molten iron and carbon dioxide gas. The limestone serves to remove impurities from the iron ore and forms a slag, which is separated from the molten iron.
• Chemical Equation: The overall chemical equation for the displacement reaction of iron oxide with carbon in a blast furnace is:iron oxide + carbon → iron + carbon dioxideThis equation represents the reduction of iron oxide (Fe2O3 or Fe3O4) to elemental iron (Fe) by carbon, with carbon dioxide (CO2) as a byproduct.
• Zinc Extraction: Another example of displacement using carbon involves the extraction of zinc from its sulfide ore, known as sphalerite (zinc blende). Zinc sulfide (ZnS) is first roasted with air to convert it into zinc oxide (ZnO). Then, the zinc oxide is reduced by heating it with carbon in a retort, producing pure zinc metal.