Before learning how to write balanced net ionic equations,
we must first learn about electrolytes.
If an aqueous solution of a compound conducts electricity,
it is called an electrolyte. The ability to conduct electricity
results from the dissociation of the compound into ions in solution.
There are two types of electrolytes:
- Strong Electrolytes - in
aqueous solution, these compounds dissociate 100% and exist as
ions in solutions. They include strong acids (HCl, HBr, HI, HNO3,
H2SO4 and HClO4), strong bases
(all the Group IA and IIA hydroxides) and all soluble salts. Below
is general solubility table. We recommend that you learn it.
- Weak Electrolytes and/or nonelectrolytes
- in aqueous solution, these compounds yield few to no ions in
solution and should be represented by the molecular formula. They
include: water, weak acids (any acid that isn't strong), weak
bases (any base that isn't strong) and nonelectrolytes.
Once you have learned the types of electrolytes, writing a balanced
equation is best explained by example.
Write the balanced net ionic equation for the reaction of aqueous
sodium hydroxide and aqueous hydrochloric acid
Step #1: Write
the balanced GENERAL EQUATION - In order to write
this equation, you must decide what the products are. This example
problem is an acid-base
reaction. The products will be a salt (NaCl) and water. After
you have written the reaction, it must be balanced.
Write the TOTAL IONIC EQUATION - Here, each reactant and
product is studied to determine whether it dissociates in solution.
If it is a strong electrolyte, it is written as ions. If it isn't
a strong electrolyte it is written as a molecule.
Because NaOH, HCl and NaCl are strong electrolytes
they are written as ions. Water is a nonelectrolyte and should
be written as a molecule.
Step #3: Write the NET
IONIC EQUATION - Each species that does not undergo a change
is called a "spectator ion". These species are removed
from the equation leaving the balanced net ionic equation
In this example, Na+ and Cl- are spectator ions. They do not
undergo change in the reaction. Therefore, they are removed.
Try a few problems on your own.
Problem #1: Write
a balanced net ionic equation for the reaction of solid sodium hydroxide
with nitric acid.
Problem #2: Write
a balanced net ionic equation for the reaction of aqueous silver
nitrate with aqueous sodium chloride
Problem #3: Write
a balanced net ionic equation for the reaction of solid barium sulfate
with sodium carbonate.