Global challenges Study Guide

The method used to extract a metal from its ore depends on the metal's position in the reactivity series relative to carbon. Metals that are more reactive than carbon, such as aluminium, magnesium, and sodium, cannot be extracted by reduction with carbon because carbon is not strong enough to 'take' the oxygen from these metal oxides. Instead, these highly reactive metals are typically extracted using electrolysis, which is an energy-intensive process involving the decomposition of a molten compound using an electric current. This method is expensive due to the high energy requirements. Metals that are less reactive than carbon, such as iron, lead, tin, and zinc, can be extracted from their oxides by heating with carbon. Carbon is more reactive than these metals, so it can reduce their oxides by removing the oxygen from them. This is a common and relatively cheaper method of extraction. For example, iron is extracted from haematite (iron(III) oxide) by reduction with carbon in a blast furnace. Metals that are very unreactive, like gold and silver, often exist in their native, uncombined form and therefore require little to no chemical extraction from ores; they are simply mined and then separated physically. Understanding the reactivity series helps determine the most economically viable and chemically effective extraction process for a given metal.

Condensation polymerisation involves monomer molecules reacting to form a polymer and a small molecule byproduct, usually water. In a school laboratory, a common demonstration making nylon shows this process. One monomer, typically a diamine like hexane-1,6-diamine, is dissolved in an alkali such as sodium hydroxide solution. The other monomer, a diacyl chloride like decanedioyl dichloride, is dissolved in an immiscible organic solvent, for example, hexane. These two solutions are carefully layered one on top of the other in a beaker to form two distinct layers. The key to successful polymerisation is to avoid mixing the layers initially. At the interface where the two liquids meet, the condensation reaction occurs, forming a solid polymer film. This film can then be carefully pulled from the interface using a pair of forceps. As the polymer is removed, fresh monomer solutions are brought into contact, allowing continuous polymer formation. This creates a 'nylon rope'. The polymer is then washed with water to remove unreacted monomers and byproducts before being dried. Safety precautions include wearing eye protection due to the corrosive nature of sodium hydroxide and the irritant properties of the organic solvent and acid chloride. Good ventilation is also important due to the volatile organic solvent.