Precipitation Reactions
(dissolution animation)
Animation for NaCl dissolving in H2O
When you mix two aqueous ionic compounds together, there are two possible outcomes:
1) a chemical reaction occurs (a gas, water, or a precipitate forms)
2) no reaction occurs (all reactants and products are aqueous)
A reaction between two chemicals dissolved in water may be shown in three ways:
(1) Molecular Equation – The equation is written as if all the chemicals consist of
molecules.
BaCl2 (aq) + Na2SO4 (aq) à BaSO4 (s) + 2 NaCl (aq)
(2) Total Ionic Equation - The equation is written to show the dissociation (separation) of
ionic compounds into their respective ions when they dissolve in water.
Ba2+ (aq) + 2Cl- (aq) + 2Na+ (aq) + SO42- (aq) à BaSO4 (s) + 2Na+ (aq) + 2Cl- (aq)
(3) Net Ionic equation – The equation is written to show only the ions or molecules which
are actively involved in the reaction.
Ba+2 (aq) + SO4-2 (aq) à
BaSO4 (s)
Note that the sodium and chlorine ions were eliminated since they did not take part in the
reaction. Ions like this, which occur in the same form on both sides of the equation, are
called spectator ions.
*An insoluble solid formed from the mixing of two ionic solutions is known as a precipitate.
**We can use a solubility tables to predict whether or not a precipitate will form when two
solutions are mixed.
Try this: Write three types of equations (molecular, total and net ionic) for each of the
following reactions :
(1) AgNO3
+ K2CO3 
(2) Na3PO4
+ MgSO4 
(3) SnSO4 + Na2S 
(4) FeBr3
+ KOH 
(5) SnCl2
+ K3PO4 