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Before learning how to write balanced net ionic equations,
we must first learn about electrolytes.
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.
Example #1: 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.
Step #2: 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.
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