Chemistry lesson: Net Ionic Equations

It is important to be able to write net ionic equations in order to know which entities are directly involved in a chemical reaction. Those entities that are not involved in the reaction are referred to as spectator ions and are removed from the equation. The remaining chemical entities are those that undergo a chemical change. This tutorial illustrates how a net ionic equation is derived from a balanced non-ionic equation. The following is a typical problem grade 11 chemistry students are required to solve.

Practice:

Write the net ionic equation for the neutralization of aqueous barium hydroxide with sulphuric acid.

Step #1 – Write the balanced non-ionic equation:

$Ba(OH)_{2(aq)} + H_2SO_{4(aq)} \to BaSO_{4(aq)} + 2H_2O_{(l)}$

Step #2 – Separate all soluble species and assign valence charges.

$Ba^{+2} _{(aq)} + 2OH^{+1} _{(aq)} + 2H^{+1} _{(aq)} + SO_{4(aq)} ^{+2} \to Ba^{+2} _{(aq)} + SO_{4(aq)} ^{+2} + 2H_2O_{(l)}$

Step #3 – Identify and eliminate all spectator ions. These are the ions that have the same valence charge on the left and right hand side of the equation. Once the spectator ions have been eliminated the result is a net ionic equation:

$2OH^{+1} _{(aq)} + 2H^{+1} _{(aq)} \to 2H_2O_{(l)}$