How are metals extracted from their ores, and how does the method depend on reactivity?
Metal ores and oxidation, extracting metals by reduction with carbon, extracting reactive metals by electrolysis, the position of carbon in the reactivity series, and predicting reactions of Group 1 and Group 7 elements.
A focused answer to OCR Gateway GCSE Chemistry A topic C4.1 on extracting metals and predicting reactions, covering metal ores, extraction by reduction with carbon, electrolysis of reactive metals, the role of carbon in the reactivity series, and predicting the reactions of Group 1 and Group 7 elements.
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What this dot point is asking
OCR wants you to explain that most metals are found as ores (compounds, usually oxides), describe how metals are extracted by reduction with carbon or by electrolysis depending on their reactivity, link extraction to the position of carbon in the reactivity series, and predict the reactions of Group 1 and Group 7 elements. This applies the reactivity series and redox.
Metal ores and oxidation
Very unreactive metals such as gold are found native (as the uncombined metal) because they do not react with oxygen.
Extraction by reduction with carbon
This works only because the metal is below carbon in the reactivity series, so carbon is reactive enough to take the oxygen.
Extraction by electrolysis
So the position of carbon in the reactivity series is the dividing line: metals below carbon are reduced with carbon; metals above carbon are electrolysed.
Predicting reactions of Group 1 and Group 7
Using the trends from the periodic table:
- Group 1 (alkali metals): reactivity increases down the group, so reactions with water and oxygen get more vigorous lower down. A Group 1 metal reacts to form a ion.
- Group 7 (halogens): reactivity decreases down the group. A more reactive halogen (higher up) will displace a less reactive halogen (lower down) from a solution of its salt, for example chlorine displaces bromine from potassium bromide.
By knowing these trends you can predict products and whether a reaction occurs.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20194 marksIron is extracted by heating iron oxide with carbon, but aluminium is extracted by electrolysis. Explain why the two metals are extracted by different methods, using the reactivity series.Show worked answer →
A C4.1 structured question. Reward: a metal can be extracted by heating its oxide with carbon only if the metal is less reactive than carbon, because carbon can then displace (reduce) the metal from its oxide. Iron is less reactive than carbon, so carbon reduces iron oxide to iron. Aluminium is more reactive than carbon, so carbon cannot displace aluminium from its oxide; aluminium must instead be extracted by electrolysis of its molten oxide. Markers credit the idea that carbon can reduce metals less reactive than itself (iron), but cannot reduce metals more reactive than itself (aluminium), which must be electrolysed. A common slip is to get the carbon comparison the wrong way round.
OCR 20224 marksCopper oxide is reduced by carbon: 2CuO + C produces 2Cu + CO2. Explain, in terms of oxygen and of reduction, what happens to the copper oxide and to the carbon in this reaction.Show worked answer →
A Higher tier redox question on extraction. Reward: the copper oxide is reduced because it loses oxygen (it goes from CuO to Cu); the carbon removes the oxygen from the copper oxide, so carbon is the reducing agent. The carbon is oxidised because it gains oxygen (it goes from C to CO2). So this is a redox reaction: copper oxide is reduced (loses oxygen) and carbon is oxidised (gains oxygen). Markers credit copper oxide reduced (loses oxygen), carbon oxidised (gains oxygen), and identifying carbon as the reducing agent. A common error is to say the carbon is reduced.
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