Download 3.4 Writing Formula, Complete and Net Ionic Equations


Objective:
write a formula equation, complete ionic equation,
and net ionic equation that represent a reaction

We must be able to represent a reaction in
three different ways:
 Formula Equation
 Total or Complete Ionic Equation
 Net Ionic Equation

A balanced chemical equation in which all the reactants
and products are given by their chemical formula.
For Example:
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)



Soluble species are indicated by placing “(aq)” after the
formula.
Precipitates are indicated by placing “(s)” after the formula.
This way of expressing the reaction is used whenever we
want to indicate the chemical formula of the reactants and
products.
Ion
Solubility
Exceptions
NO3–
soluble
none
ClO4–
soluble
none
Cl–
soluble
I–
soluble
except Ag+, Hg22+, *Pb2+
SO42-
soluble
except Ca2+, Ba2+, Sr2+,
Hg2+, Pb2+, Ag+
CO32-
insoluble
except Group IA and
NH4+
PO43-
insoluble
except Group IA and
NH4+
OH–
insoluble
except Group IA, *Ca2+,
Ba2+, Sr2+
S2-
insoluble
except Group IA, IIA
and NH4+
Na+
soluble
none
K+
soluble
none
NH4+
soluble
none
except Ag+, Hg22+, *Pb2+
Shows all the soluble ionic species broken up into their respective ions.
For Example:
Ag+(aq)+ NO3-(aq)+ Na+(aq)+ Cl-(aq) → AgCl(s)+ Na+(aq)+ NO3-(aq)


This method is not frequently used because it is cumbersome to write out.
It is used to emphasize the situation which exists before and after the
reaction.
Spectator ions:

Ions that remain unchanged during a reaction and do not participate in the
reaction.They are present on both sides of the equation.

The spectator ions in the above equation are NO3-(aq) and Na+(aq)
NEVER write a total ionic equation until you have first written a balanced
formula equation.

If you proceed directly to a total ionic equation the result may be balanced
but still may not represent the actual situation.


Shows only the reacting species (species which are actively involved
in the reaction…the one making the PPT) in the equation.
The net ionic equation is formed by omitting the spectator
ions from the total ionic equation.
For Example:
We had:
then:
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
Ag+(aq)+ NO3-(aq)+ Na+(aq)+ Cl-(aq) → AgCl(s)+ Na+(aq)+ NO3-(aq)
Canceling out spectator ions, we get:
Ag+(aq)+ Cl-(aq) → AgCl(s)


Example:
Write a formula equation, a total ionic
equation, and a net ionic equation for the
reaction which occurs when solutions of
Al(NO3)3(aq) and MgS(aq) are mixed.

1)
2)
3)
Write the formula, complete ionic, and net
ionic equation for each of the following
reactions:
Aqueous nickel (II) chloride reacts with
aqueous sodium hydroxide to give nickel (II)
hydroxide and sodium chloride.
Solid potassium metal reacts with water to
give potassium hydroxide and hydrogen gas.
Aqueous sodium hydroxide reacts with
phosphoric acid to give water and sodium
phosphate.