Notes on Net Ionic Equations
Most reactions in an aqueous medium involve ions. However, when a reaction takes place two
kinds of ions usually emerge: (1) "spectator" ions and (2) "player" ions. The names imply the
character of the ions with respect to the reaction. Player ions are directly in the reaction whereas
spectator ions fulfill the role of spectators and their primary function is keeping electrical
neutrality in the solution. Consider the precipitation reaction that occurs when aqueous solutions
of sodium chloride and silver nitrate are mixed. A white precipitate of AgCl forms. The chemical
equation for this reaction is written as:
This equation contains all ions in the solution. However, sometimes it’s necessary to only
include those ions that are players and leave out the spectators. A chemical equation that contains
only the player ions is called the net ionic equation (nie). To get the nie (1) write out all soluble
compounds as ions and (2) eliminate ions common to both reactants and products. The resulting
chemical equation is then the nie. For the equation above we have: (for step 2 move the mouse
over the reaction)
The resulting equation is the net ionic equation,
While the above reaction is particularly simple (i.e. all stoichiometric coefficients are equal to 1),
More complex nie's result from a similar procedure. For example, if iron(III) nitrate is mixed
with ammonium sulfide a yellow precipitate of iron(III) sulfide results. The nie for this reaction
is:
So to describe these reactions that occur in solution, write the equation for the
reaction in ionic form, indicating the ionic species that actually exist in solution.
Another example is describing the reaction of a solution of BaCl 2 with a solution of Na2SO4
to form the insoluble solid BaSO4 we would write
2Na1+(aq) + SO42-(aq) + Ba2+(aq) + 2Cl1-(aq) -----> 2Na1+(aq) + 2Cl1-(aq) + BaSO4(s)
In writing a total ionic equation for reactions in water:
1. We indicate all soluble ionic materials as ions, followed by (aq).
2. All substances that react with water to form ions are written as ions followed
by (aq).
3. All insoluble ionic solids are written with (s) following their formula.
4. All soluble unionized species are written with their molecular formula followed
by (aq).
5. In the above equation, we note that the sodium and chloride ions are
unchanged and are present on both sides of the equation. Since they are not
undergoing chemical reaction, they can be referred to as spectator ions. If
we subtract the spectator ions from each side of the equation, we then have a
net ionic equation. The net ionic equation for the above reaction is:
Ba2+(aq) + SO42-(aq) -----> BaSO4(s)
The net ionic equation is a statement of the chemistry that occurred, namely, aqueous
barium 2+ ion reacted with aqueous sulfate ion to form solid barium sulfate.
Net ionic equations may also be written for replacement reactions.
Replacement
1. iron filings added to copper(II) sulfate in solution
2. aluminum metal in hydrochloric acid
3. potassium metal added to cold water
4. silver added to aqueous copper(II) sulfate
5. zinc metal added to mercury(II) nitrate
6. chlorine gas bubbled through a solution of calcium bromide
Ionic
1. potassium iodide added to lead(II) nitrate
2. sodium sulfite combined with acetic acid
3. a solution of sodium chloride added to dilute sulfuric acid
4. barium nitrate added to sodium oxalate
5. sodium bicarbonate added to hydrochloric acid
Practice Writing Net Ionic Equations
Key
Replacement
1. iron filings added to copper(II) sulfate in solution
Fe(s) + Cu2+(aq) + SO4(aq)2- ----> Cu(s) + Fe2+(aq) + SO4(aq)22. aluminum metal in hydrochloric acid
Al(s) + 6H1+(aq) + 6Cl1-(aq) ----> Al3+(aq) + 6Cl1-(aq) + 3H2(g)
3. potassium metal added to cold water
K(s) + H2O(l) ----> K1+(aq) + OH1-(aq) + H2(g):
4. silver added to aqueous copper(II) sulfate
2Ag(s) + Cu2+(aq) + SO42-(aq) ----> 2Ag1+(aq) + Cu(s) + SO42-(aq)
5. zinc metal added to mercury(II) nitrate
Zn(s) + Hg2+(aq) + 2NO31-(aq) ----> Zn2+(aq) + Hg(l) + 2NO31-(aq)
6. chlorine gas bubbled through a solution of calcium bromide
Cl2(g) + Ca2+(aq) + 2Br1-(aq) ----> Ca2+(aq) + 2Cl1-(aq) + Br2(l)
Ionic
1. potassium iodide added to lead(II) nitrate
KI(aq) + Pb(NO3)2(aq) ----> KNO3 + PbI2
2. sodium sulfite combined with acetic acid
Na2SO3(aq) + HC2H3O2(aq) ---->
3. a solution of sodium chloride added to dilute sulfuric acid
NaCl(aq) + H2SO4(aq) ----> no reaction
4. barium nitrate added to sodium oxalate
Ba(NO3)2(aq) + Na2C2O4(aq) ----> BaC2O4
5. sodium bicarbonate added to hydrochloric acid
NaHCO3(aq) + HCl(aq) ---->