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Writing Net Ionic Equations

We will find net ionic equations extremely useful for summarizing a great deal of information with relatively little effort.

Three Types of Equations Are Used to Describe Reactions in Solution:

1. The formula (total) equation gives the overall reaction stoichiometry but not necessarily the actual forms of the reactants and products in solution.

2. The complete ionic equation represents as ions all reactants and products that are strong electrolytes.

3. The net ionic equation includes only those solution components undergoing a change. Spectator ions are not included.

When sodium chloride solution is added to silver nitrate solution, a precipitate of silver chloride is produced, and the solution contains sodium nitrate:

This type of equation can be called the total equation. (A total equation is sometimes referred to as a molecular equation because the compounds in it are written “as if they were molecules.”)

Even more informative than a total equation is an ionic equation. An ionic compound in aqueous solution may be represented as separate ions, but an ionic solid that is not dissolved in water is written as a complete compound. We can write an ionic equation for the reaction of sodium chloride with silver nitrate in aqueous solution as follows:

Because the Na⁺ and NO₃^- ions appear on both sides of this equation (unchanged by the reaction), they are called spectator ions. They may be eliminated from the equation:

This equation is an example of a net ionic equation. All the spectator ions are omitted from a net ionic equation.

While we are learning to write net ionic equations, we will use the following procedure. After we get used to working with them, we will be able to write them directly and save even more effort with their use.

1. Start with a total equation for the reaction, making sure that it is balanced.

2. Write all compounds that are both soluble and ionic in the form of their separate ions, making sure to have the correct number of ions of each type. Write all other compounds (for example, gases, other covalent compounds, and all solids) as complete compounds.

3. Eliminate the ions that are unchanged on both sides of the equation to obtain the net ionic equation.

Be careful not to misinterpret the name net ionic equation. It is not necessarily true that all the substances appearing in such an equation are ionic. Covalent compounds often occur in net ionic equations. Also, just because the formula for a complete compound is written in such an equation does not mean that the compound is not ionic; it might simply be insoluble.

Don’t be confused about what should be included in net ionic equations. It is easier to remember what should be left out: Only ions in solution that remain unchanged in solution should be left out to produce net ionic equations; all other species must be included. Thus, insoluble compounds (ionic or not), covalent compounds, elements, and ions that change in any way between reactants and products are all included.