A metal's reactivity decides whether it is found native or must be extracted
Definition
Reactivity series
A list of metals arranged in order of reactivity, with carbon and hydrogen included as useful reference points.
Definition
Ore
A rock that contains enough of a metal compound to make extracting the metal worthwhile.
- The reactivity series predicts how a metal occurs naturally and how it must be extracted.
- Very unreactive metals such as gold barely react with other elements, so they are found as the metal itself.
- Most metals are reactive enough to be found combined in compounds within rocks called ores.
- Extraction is the process of obtaining a metal from one of its compounds.
- Extracting most metals needs a chemical reaction that changes the metal compound into the metal.
Key Idea
- Unreactive metals such as gold can be found native, as the uncombined metal.
- Most metals are found as compounds and must be chemically extracted.
Carbon extracts metals that are less reactive than carbon
Definition
Compound
A substance containing atoms of two or more different elements chemically bonded together.
- Metals below carbon in the reactivity series can be extracted by heating their oxides with carbon.
- The carbon removes the oxygen from the metal oxide, leaving the metal.
- metal oxide+carbon→metal+carbon dioxide\text{metal oxide} + \text{carbon} \rightarrow \text{metal} + \text{carbon dioxide}metal oxide+carbon→metal+carbon dioxide
- Metals above carbon, such as aluminium, cannot be extracted this way and need electrolysis instead.
- For example, copper oxide with carbon: 2CuO(s)+C(s)→2Cu(s)+CO2(g)2\text{CuO}(s) + \text{C}(s) \rightarrow 2\text{Cu}(s) + \text{CO}_2(g)2CuO(s)+C(s)→2Cu(s)+CO2(g)
Note
You are not expected to recall the industrial machinery or furnace stages; the chemistry of removing oxygen is what matters.
Tracking the oxygen shows which substance is reduced and which is oxidised
- Reduction is the loss of oxygen, and oxidation is the gain of oxygen.
- Compare each reactant with its product to see which gained and which lost oxygen.
- In carbon extraction, the metal oxide is reduced because it loses oxygen to become the metal.
- The carbon is oxidised because it gains oxygen to form carbon dioxide.
- Oxidation and reduction happen together, because the oxygen is transferred from the oxide to the carbon.
Common Mistake
- Do not say carbon is reduced just because it causes the reduction; carbon itself is oxidised.
- For this topic, identify oxidation and reduction only by the gain or loss of oxygen.
Evaluating an extraction process means using the evidence you are given
Definition
Element
A substance made of atoms that all have the same number of protons.
- When you are given a process, first identify the metal compound and the substance that removes the oxygen.
- Check whether the metal is less reactive than carbon before deciding whether carbon reduction could work.
- Weigh up the evidence provided, such as energy use, temperature, cost, carbon dioxide released and the amount or purity of metal.
- A process running at a lower temperature may use less energy and cost less, if the data supports that.
- A process releasing more carbon dioxide may have a greater environmental impact.
- Support your judgement with specific figures from the information rather than inventing details.
Self review
- Why can gold be found as the uncombined metal?
- Which metals can be extracted from their oxides using carbon?
- Define reduction in terms of oxygen.
- In the reaction of copper oxide with carbon, which substance is oxidised and why?
- What kind of evidence should support an evaluation of an extraction process?
