Net Ionic Equations
Unit:  Chemical Reactions/Descriptive Chemistry
Skills:
•	identify ions that dissociate
•	identify spectator ions
•	write net ionic equations
	Notes:
net ionic equation:  a chemical equation that shows only ions or pure substances that are changed in the reaction
spectator ion:  an ion that remains in solution and does not participate in a chemical reaction
If you mixed aqueous solutions of calcium chloride (CaCl2 (aq)) and sodium nitrate (NaNO3 (aq)), will a reaction happen?
CaCl2 (aq) + NaNO3 (aq)  ?
Step 1: The aqueous (aq) compounds have completely dissociated in solution, so that means they are ions:
Symbol	Meaning	
CaCl2 (aq)	Ca2+ (aq) + Cl− (aq)	
NaNO3 (aq)	Na+ (aq) + NO3− (aq)	
Ca(NO3)2 (aq)	Ca2+ (aq) + NO3− (aq)	
NaCl (aq)	Na+ (aq) + Cl− (aq)	
Step 2: The cations change places, and you get:
CaCl2 (aq) + 2NaNO3 (aq)  Ca(NO3) 2  + 2NaCl 
Step 3: if the compound is soluble, write (aq).  If insoluble, write (s).  Both of these compounds are soluble, so we write:
CaCl2 (aq) + 2NaNO3 (aq)  Ca(NO3) 2 (aq) + 2NaCl (aq)
This means that what we really have in the beaker is:
Ca2+ (aq) + 2Cl− (aq) + 2Na+ (aq) + 2NO3− (aq)  Ca2+ (aq) +  2NO3− (aq) + 2Na+ (aq) + 2Cl− (aq)
The above is called a complete ionic equation.
Notice that the right side and the left side contain exactly the same ions.  In other words, nothing has changed.  If no substances are changed—no chemical bonds are formed or broken—then no chemical reaction has occurred!
Consider the reaction of aqueous silver nitrate with aqueous sodium carbonate:
AgNO3 (aq) + Na2CO3 (aq)  Ag2CO3 (s) + NaNO3 (aq)
Notice that one of the products, silver carbonate, forms a solid (precipitate).
The complete ionic equation would look like this:
Ag+ (aq) + NO3− (aq) + Na+ (aq) + CO32− (aq)  Ag2CO3 (s) + Na+ (aq) + NO3− (aq)
If we cancel out the spectator ions (ions that are unchanged by the reaction) Na+ and NO3−:
Ag+ (aq) + NO3− (aq) + Na+ (aq) + CO32− (aq)  Ag2CO3 (s) + Na+ (aq) + NO3− (aq)
we are left with the unbalanced net ionic equation for this reaction:
Ag+ (aq) + CO32− (aq)  Ag2CO3 (s)
The balanced net ionic equation would therefore be:
2 Ag+ (aq) + CO32− (aq)  Ag2CO3 (s)
AP Exam Strategies:
•	Always write balanced net ionic equations unless you are explicitly told otherwise.
•	Reactions in question #4 (the descriptive chemistry question) on the AP exam always happen.
•	Remember that for oxidation-reduction (redox) reactions, electrons and charges must balance as well as atoms.