Balancing Net Ionic Equations

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:

  1. 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.

  1. 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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