Reactivity Series and Metal Extraction: Question 5

Syllabus 9.6

Multiple choice Core 1 mark

Four hypothetical metals, J, K, L and M, have positions in the reactivity series relative to carbon given by

$J > K > \text{carbon} > L > M$

(with J the most reactive and M the least reactive of the five).

Which statement about extracting these metals from their ores is correct?

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Step 1: Recall the rule linking reactivity to extraction method

The ease of obtaining a metal from its ore depends on its position in the reactivity series:

Metals above carbon are too reactive to be displaced by carbon, so they must be extracted using electrolysis.
Metals below carbon are less reactive than carbon, so carbon can reduce their ores by removing the oxygen. These metals can be extracted by heating with carbon.

Step 2: Apply the rule to J, K, L and M

The given order is $J > K > \text{carbon} > L > M$ , so:

J and K are above carbon $\rightarrow$ they need electrolysis.
L and M are below carbon $\rightarrow$ they can be extracted by heating with carbon.

Step 3: Check each option

A: J is above carbon, so it needs electrolysis, not carbon reduction, incorrect.
B: K is above carbon, so it needs electrolysis, not carbon reduction, incorrect.
C: L is below carbon, so heating its oxide with carbon will reduce it to the metal, correct.
D: M is below carbon, so it can be extracted more cheaply by carbon reduction; electrolysis is not the only method, incorrect.

Final answer

L can be extracted by heating its oxide with carbon, option C.

Common mistakes

Choosing an option that extracts J or K using carbon, by assuming any metal can be extracted this way regardless of its reactivity, rather than recognising that only metals BELOW carbon in the series can be reduced by heating with carbon.
Believing electrolysis is the "only" way to extract a metal below carbon (such as M), rather than recognising that metals below carbon are more easily and cheaply extracted by carbon reduction, so electrolysis is not needed at all for them.
Confusing the direction of the list, thinking the metals nearer the top (J, K) are the ones extracted using carbon reduction, rather than the metals nearer the bottom (L, M).
Assuming a metal's position relative to carbon only affects the cost of extraction, rather than which method can be used to extract it at all.