Question Video: Identifying a Spectator Ion in a Simple Redox Reaction Chemistry

A redox reaction is described by the equation: Mg (s) + CuSO₄ (aq) ⟶ MgSO₄ (aq) + Cu (s). Including the state symbol, identify the spectator ion in this reaction.

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Video Transcript

A redox reaction is described by the equation Mg solid plus CuSO4 aqueous reacting to form MgSO4 aqueous plus Cu solid. Including the state symbol, identify the spectator ion in this reaction.

The reaction in this question, where solid magnesium metal is reacting with copper(II) sulfate to form magnesium sulfate and copper metal, is an example of a redox reaction that involves the transfer of electrons. But the fact that this reaction is a redox reaction isn’t important for answering this question, since all we’ve been tasked with is identifying a spectator ion. A spectator ion is an ion that does not participate in the chemical change in a reaction.

To identify these spectator ions, we’ll first have to write out the ionic form of all the chemical species involved in this reaction. We’ll notice that some of the chemical species involved in this reaction, copper sulfate and magnesium sulphate, are aqueous. When we have an ionic substance that’s aqueous, that means it’s split up into the ions that make it up. So let’s go through our chemical equation and split up everything into ions.

Our first reactant is magnesium metal. Since it’s a solid, we don’t have to do anything with it. Next is copper(II) sulfate, which would be split up into the copper two plus ion and the sulfate two minus ion. Our first product is magnesium sulfate, which would be split up into the magnesium two plus ion and the sulfate two minus ion. And our final product is solid copper. Again since this is a solid, we just leave it alone. Now that we’ve written our chemical equation with everything split up into ions that can be, which is called an ionic equation, we can identify our spectator ion. Since a spectator ion doesn’t participate in the chemical change, it will be the same on both the reactant side and the product side of our reaction.

We can see that the sulfate ion is on the reactant side and the product side. So this must be our spectator ion. So the spectator ion is sulphate or SO42−. And we shouldn’t forget the state symbol, which is aqueous.

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