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.