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An ionic equation is a chemical equation that represents a solution of mineral salts, dissociated into ions, in an aqueous medium . They generally represent the behavior of salts dissolved in water, and ionic species are written followed by the (aq) term in the equation to indicate that they are in aqueous solution.
Ions in aqueous solution are held in solution stably by ion-dipole interactions with water molecules. The ionic equations can also be applied for any electrolyte that dissociates in a polar solvent. In a balanced (balanced) ionic equation, the number of atoms of each element is the same on both sides of the reaction equation, just as it is in all other chemical equations. Also, the net charge must be the same on both sides of the equation.
Strong acids, strong bases, and soluble ionic compounds (usually salts) occur as dissociated ions in an aqueous solution, so they are written as ions in the ionic equation. Aqueous solutions of weak acids and bases and insoluble salts are generally described using molecular (nonionic) formulas, since only a small fraction of the compounds dissociates into ions.
ionic equation example
Ag + (aq) + NO 3 – (aq) + Na + (aq) + Cl – (aq) → AgCl(s) + Na + (aq) + NO 3 – (aq)
The above equation is the ionic equation of the following chemical reaction:
AgNO 3 (aq) + NaCl(aq) → AgCl(s) + NaNO 3 (aq)
Net ionic equations and complete ionic equations
The two most common forms of ionic equations are complete ionic equations and net ionic equations. The complete ionic equation lists all the ions that dissociate in the chemical reaction . The net ionic equation cancels the ions that appear on both sides of the reaction since they do not participate in the adjustment of the reaction . The ions that cancel are called “spectator ions”.
For example, the reaction between silver nitrate (AgNO 3 ) and sodium chloride (NaCl) in an aqueous medium is expressed in a complete ionic equation as follows (the s in parentheses indicates that the compound is in the solid state, which is a precipitate in the reaction)
Ag + (aq) + NO 3 – (aq) + Na + (aq) + Cl – (aq) → AgCl(s) + Na + (aq) + NO 3 – (aq)
It can be seen that the sodium cation Na + and the nitrate anion NO 3 – appear on both the reactant and product sides. If they cancel, the net ionic equation can be written as
Ag + (aq) + Cl – (aq) → AgCl(s)
In this example the coefficient that multiplies each compound is 1 and therefore it is omitted. But if there were coefficients other than 1 and they had a common divisor, they would have to be divided by that common divisor to express the net ionic equation with the smallest integer values of the coefficients.
Both the complete ionic equation and the net ionic equation must be balanced equations.
Fountain
Brady, James E. Chemistry: Matter and its Changes . 5th edition , John Wiley & Sons, December 2007.
