Edexcel GCSE Chemistry (1CH0) — Extracting Metals and Equilibria
If you dig up a nugget of pure gold, you can polish it and wear it immediately, but if you dig up iron ore, you just have a rusty rock. Very unreactive metals like gold, silver, and platinum are highly resistant to oxidation and are found in the Earth's crust as pure, uncombined elements called native metals.
Most other metals are found combined with other elements (usually oxygen) in rocks called ores. To get the pure metal, it must be extracted from its compound. The method chosen to extract a metal depends entirely on its position in the reactivity series relative to carbon.
Metals positioned below carbon in the reactivity series (such as zinc, iron, tin, lead, and copper) are extracted by heating their metal oxides with carbon. This works via a displacement reaction because carbon is more reactive than these metals and can strip the oxygen away from them.
This is a redox reaction. The metal oxide is reduced (loses oxygen) to form the pure metal, while the carbon acts as a reducing agent and is oxidised (gains oxygen) to form carbon dioxide.
Economically, this is the preferred method wherever possible. Carbon (often used in the form of coke) is very cheap and also acts as a fuel, burning to provide the high thermal energy needed for the extraction process.
Metals positioned above carbon in the reactivity series (such as potassium, sodium, calcium, magnesium, and aluminium) cannot be extracted by heating with carbon. Carbon is not a strong enough reducing agent to displace these highly reactive metals from their stable oxides. Instead, these metals must be extracted using electrolysis.
Electrolysis involves passing an electric current through a molten ionic compound (the electrolyte) to decompose it. The ore must be molten because ions are not free to move in a solid state, and mobile ions are required to conduct electricity.
This extraction method is extremely expensive due to the massive electricity requirements and the thermal energy needed to melt the ores. To reduce costs, aluminium oxide is dissolved in molten cryolite, which significantly lowers its melting point from over 2000°C to around 900°C. Additionally, the positive carbon electrodes (anodes) continually react with the oxygen produced to form carbon dioxide (), meaning they burn away and must be regularly replaced at an extra cost.
Because high-grade ores are running out, alternative methods are used to extract metals from low-grade ores (rocks containing very little metal). These methods are slower but more environmentally friendly.
Phytoextraction involves growing plants in soil containing metal compounds. The plants absorb the metal ions through their roots and concentrate them in their leaves. The plants are then harvested and burned to produce an ash, from which the pure metal can be extracted.
Bioleaching uses bacteria to break down metal ores. The bacteria produce an acidic solution called a leachate which contains the dissolved metal ions. The metal can then be extracted from the leachate using displacement (e.g., adding scrap iron) or electrolysis.
Because extracting metals from their ores is so energy-intensive and expensive, recycling plays a crucial role in modern industry. Recycling aluminium requires only 5–10% of the energy needed to extract it from its ore via electrolysis.
Recycling is economically beneficial because it avoids the high costs of electricity and heating. Environmentally, it conserves finite resources (ores that will eventually run out) and reduces the volume of waste sent to landfill sites.
Students often state that metals above carbon are extracted by electrolysis because it is 'a stronger method', but the correct scientific reason is that carbon is simply not reactive enough to displace them from their oxides.
In 6-mark questions explaining extraction choice, examiners expect you to explicitly link three concepts: the metal's position relative to carbon, the specific extraction method used, and the economic justification (cost of electricity vs. cheap carbon).
Always use the word 'molten' when describing the state of the ore during electrolysis; examiners will not award marks if you simply write 'liquid' or imply the solid ore can conduct electricity.
If asked why we recycle metals, always give two distinct reasons: one environmental (conserving finite resources/ores) and one economic (saving vast amounts of energy/electricity).
Oxidation
A chemical reaction involving the gain of oxygen by a substance (or the loss of electrons).
Native metals
Unreactive metals found in the Earth's crust as pure elements, not chemically combined with other elements.
Ores
Rocks containing a high enough concentration of a metal or metal compound to make it economically worthwhile to extract.
Reactivity series
A list of metals arranged in order of their reactivity, from most reactive to least reactive.
Displacement reaction
A reaction where a more reactive element takes the place of a less reactive element in a compound.
Redox reaction
A reaction in which both reduction and oxidation occur simultaneously.
Reduced
A substance that has lost oxygen (or gained electrons) during a chemical reaction.
Reducing agent
A substance that removes oxygen from another substance, causing it to be reduced, and is itself oxidised in the process.
Oxidised
A substance that has gained oxygen (or lost electrons) during a chemical reaction.
Coke
An impure, inexpensive form of carbon used in extraction as both a fuel and a reducing agent.
Electrolysis
The process of breaking down an ionic compound using a direct electric current.
Molten
A substance that has been heated to a high enough temperature to turn from a solid into a liquid.
Electrolyte
A liquid or solution containing free-moving ions that is broken down by electricity.
Cryolite
A compound used in the extraction of aluminium to lower the melting point of aluminium oxide.
Low-grade ores
Rocks that contain only a very small percentage of metal compounds.
Phytoextraction
The use of plants to absorb metal compounds from soil, which are then harvested and burned to extract the metal from the ash.
Bioleaching
The use of bacteria to break down low-grade metal ores, producing a solution of metal ions.
Leachate
The acidic solution containing dissolved metal ions produced during bioleaching.
Finite resources
Resources that are being used up faster than they can be replaced and will eventually run out.
Put your knowledge into practice — try past paper questions for Chemistry
Oxidation
A chemical reaction involving the gain of oxygen by a substance (or the loss of electrons).
Native metals
Unreactive metals found in the Earth's crust as pure elements, not chemically combined with other elements.
Ores
Rocks containing a high enough concentration of a metal or metal compound to make it economically worthwhile to extract.
Reactivity series
A list of metals arranged in order of their reactivity, from most reactive to least reactive.
Displacement reaction
A reaction where a more reactive element takes the place of a less reactive element in a compound.
Redox reaction
A reaction in which both reduction and oxidation occur simultaneously.
Reduced
A substance that has lost oxygen (or gained electrons) during a chemical reaction.
Reducing agent
A substance that removes oxygen from another substance, causing it to be reduced, and is itself oxidised in the process.
Oxidised
A substance that has gained oxygen (or lost electrons) during a chemical reaction.
Coke
An impure, inexpensive form of carbon used in extraction as both a fuel and a reducing agent.
Electrolysis
The process of breaking down an ionic compound using a direct electric current.
Molten
A substance that has been heated to a high enough temperature to turn from a solid into a liquid.
Electrolyte
A liquid or solution containing free-moving ions that is broken down by electricity.
Cryolite
A compound used in the extraction of aluminium to lower the melting point of aluminium oxide.
Low-grade ores
Rocks that contain only a very small percentage of metal compounds.
Phytoextraction
The use of plants to absorb metal compounds from soil, which are then harvested and burned to extract the metal from the ash.
Bioleaching
The use of bacteria to break down low-grade metal ores, producing a solution of metal ions.
Leachate
The acidic solution containing dissolved metal ions produced during bioleaching.
Finite resources
Resources that are being used up faster than they can be replaced and will eventually run out.
