Zinc reacts with dilute sulfuric
acid to form aqueous zinc sulfate and hydrogen gas. Sulfate ions are not included in
the net ionic equation for this reaction. What is the name of ions of this
sort that are not included in net ionic equations?
This problem is asking us to name
the ions that are not included in a net ionic equation, which in this case are
In order to solve this problem, let
us first create a balanced molecular equation. To the left of the reaction arrow
would be the reactants zinc and sulfuric acid. Zinc would have the chemical symbol
Zn with a state symbol of s since zinc is a solid d-block element. To create the formula for sulfuric
acid, we need to discuss that acids contain hydrogen ions H+. And this acid contains the sulfate
ion SO4 2−. A neutral sulfuric acid molecule
will therefore have the chemical formula of H2SO4. And we would add the state symbol
of aq, since it is diluted with water.
Now let us identify the products
which would be to the right of the reaction arrow as aqueous zinc sulfate and
hydrogen gas. To write the formula for zinc
sulfate, we need to discuss that the zinc ion is Zn2+ and the sulfate ion is SO4
2−. To create a neutral chemical
formula for zinc sulfate, one zinc ion will balance the charge of the one sulfate
ion. So the formula would be ZnSO4. Let us not forget to add the state
symbol of aq, since zinc sulfate is aqueous. Hydrogen gas is written as H2 since
it is diatomic with a state symbol of g.
Let us note that the molecular
equation is already balanced, and therefore no coefficients need to be added. Since we created a balanced
molecular equation, we can discuss the rules for transforming this equation into an
The first rule we will discuss is
that aqueous ionic compounds and aqueous acids are expressed in terms of component
ions. We show these compounds in terms of
ions since they both spontaneously ionize in water. So, for sulfuric acid the ions
would be H+ and SO4 2− keeping the state symbol of aq. Since there are two hydrogen ions,
we would place a coefficient of two in front of H+ in the ionic equation. For zinc sulfate, the ions would be
Zn2+ and SO4 2−, keeping the state symbol of aq.
The second rule we will discuss is
that we do not change the representation of solids, liquids, and gases because they
do not spontaneously dissociate into ions. Therefore, Zn solid and H2 gas
would not be changed in the ionic equation.
The third rule is to leave aqueous
covalent compounds that are not acids alone, since they do not break apart in water,
which does not apply to this equation.
For the last rule, we then simplify
what is left by removing any species that are the same on both the reactant and
product sides. The only ion that appears the same
on both sides is the sulfate ion, SO4 2−. And so this is eliminated from the
ionic equation. The sulphate ions do not
participate in this reaction and are called spectator ions. These ions, such as the sulfate
ions, have the same state symbol throughout the chemical reaction process and are
not featured in the net ionic equation.
Therefore, the name of the ions not
included in net ionic equations are spectator ions.