In a complete ionic equation, the chemist recognizes compounds that ionize in solution as ions and includes them in the written equation. Spectator ions are included in this equation, unlike the net ionic equation where the scientist eliminates them as they remain in the same form on both sides of the arrow.
Ionic equations involve electrolytes that dissolve in water. They include single and double displacement reactions. They sometimes form insoluble salts that precipitate from the solution or gases that bubble out of the water. For example, most carbonates are insoluble with a few exceptions. Sodium carbonate dissolves in water but reacts with barium to form an insoluble precipitate. In double replacement reactions, all the ions from the dissolved electrolytes take part in the reaction, so there are no spectator ions. In these reactions, the net ionic equation and the complete ionic equation are the same.
The law of conservation of mass dictates that the same number of elements, in this case ions, are found on each side of the chemical equation. This law helps chemists balance chemical equations. A balanced reaction uses simple whole numbers to represent the compounds or ions involved. The chemist reduces these numbers to represent the reaction using the smallest possible whole number.