What are the spectator ions in Mg(s) + Zn^(2+) + 2NO_3^(-) -> Mg^(2+) + 2NO_3^(-) + Zn(s)Mg(s)+Zn2++2NO3Mg2++2NO3+Zn(s)?

1 Answer
Jun 18, 2016

The nitrate anions, "NO"_3^(-)NO3.

Explanation:

A spectator ion is an ion that is present on both sides of a chemical equation.

In other words, in order for an ion to be a spectator ion, it must exist as such as a reactant and as a product in the balanced chemical equation.

You're dealing with a single replacement reaction in which magnesium metal, "Mg"Mg, replaces the zinc cations in zinc nitrate, "Zn"("NO"_3)_2Zn(NO3)2.

The products of this reaction are zinc metal, "Zn"Zn, and aqueous magnesium nitrate*, "Mg"("NO"_3)_2Mg(NO3)2.

The problem provides you with the complete ionic equation for this reaction

"Mg"_ ((s)) + "Zn"_ ((aq))^(2+) + 2"NO"_ (3(aq))^(-) -> "Mg"_ ((aq))^(2+) + 2"NO"_ (3(aq))^(-) + "Zn"_ ((s))Mg(s)+Zn2+(aq)+2NO3(aq)Mg2+(aq)+2NO3(aq)+Zn(s)

As you can see, the reactants' side contains two ions

  • the zinc cation, "Zn"^(2+)Zn2+
  • the nitrate anion, "NO"_3^(2-)NO23

Likewise, the product's side also contains two ions

  • the magnesium cation, "Mg"^(2+)Mg2+
  • the nitrate anion, "NO"_3^(-)NO3

Because the nitrate anions are present on both sides of the equation, they are spectator ions.

This means that you can eliminate them from the complete ionic equation

"Mg"_ ((s)) + "Zn"_ ((aq))^(2+) + color(red)(cancel(color(black)(2"NO"_ (3(aq))^(-)))) -> "Mg"_ ((aq))^(2+) + color(red)(cancel(color(black)(2"NO"_ (3(aq))^(-)))) + "Zn"_ ((s))

to get the net ionic equation

"Mg"_ ((s)) + "Zn"_ ((aq))^(2+) -> "Mg"_ ((aq))^(2+) + "Zn"_ ((s))