Ionic Equations

Ionic Equations

Ionic equations and net ionic equations are usually written only for reactions that occur in solution and are an attempt to show how the ions present are reacting. While ionic equations show all of the substances present in solution, a net ionic equation shows only those that are changed during the course of the reaction.

To write ionic equations follow the steps below. Each step will be demonstrated using the reaction of magnesium metal with hydrochloric acid as an example.

1. Write the molecular equation and balance it.

Mg + 2 HCl MgCl2 + H2

2. Determine the state of each substance (gas, liquid, solid, aqueous). Use the solubility rules to determine which of the ionic compounds are soluble in water. Soluble ionics are identified with an (aq), insoluble ones with an (s). Most elements and covalent compounds (covalent compounds are formed when two or more nonmetallic elements are bonded to each other) are insoluble in water and should be shown with an (s), (l) or (g).

Mg(s) + 2 HCl(aq) MgCl2(aq) + H2(g)

3. Write the ionic equation by breaking all the soluble ionic compounds (those marked with an (aq)) into their respective ions. Each ion should be shown with its charge and an (aq) to show that it is present in solution. Use coefficients to show the number of each ion present. Rewrite the elements and covalent compounds as they appeared in the preceding step.

Mg(s) + 2 H+(aq) + 2 Cl-(aq) Mg+2(aq) + 2 Cl-(aq) + H2(g)

4. Write the net ionic equation by removing the spectator ions. Spectator ions are those ions that appear exactly the same on each side of the ionic equation.

Mg(s) + 2 H+(aq) Mg+2(aq) + H2(g)

Try writing the ionic and net ionic equations for the double displacement reaction of silver nitrate with sodium sulfate. When you are done, check your answers.