The diagram shows part of the reactivity series, most reactive at the top. A student wants a metal that will displace zinc from zinc sulfate solution but wi...
Question 1 Report
The diagram shows part of the reactivity series, most reactive at the top. A student wants a metal that will displace zinc from zinc sulfate solution but will NOT react with cold water. Which metal fits both requirements?
Answer Details
Two separate conditions must both be met, so use the series shown in the diagram twice.
To displace zinc from zinc sulfate solution, the metal must be above zinc in the list, which rules out iron and copper: they sit below zinc and so cannot push zinc ions out of solution. That leaves potassium, calcium and magnesium.
The second condition is no reaction with cold water. Potassium reacts vigorously with cold water and calcium reacts steadily with it, both giving hydrogen and a hydroxide, so they are eliminated. Magnesium reacts only extremely slowly with cold water, needing steam for a rapid reaction, so it satisfies both requirements:
\[\mathrm{Mg + ZnSO_4 \rightarrow MgSO_4 + Zn}\]
The usual mistake is choosing the most reactive metal available. More reactive is not automatically better when a second condition limits the choice.
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