Ionic Equations and Precipitation Reactions
The following steps illustrate an approach to predicting products of precipitation reactions and writing
ionic and net ionic equations. Consider the following scenario in which two soluble ionic compounds
are mixed together. The subsequent steps show how to predict the products (if any) for the reaction and
to write valid equations.
Ba(NO3)2(aq)
+ Na2SO4(aq)
step 1: Recognize the ions that make up the two substances. We have Ba2+, NO3 , Na+ and SO42 .
step 2: Consult the solubility rules to determine whether or not an insoluble compound would form if
the ions switched partners (i.e. if Ba2+ was combined with SO42 and Na+ was combined with NO3 ).
step 3: If an insoluble product is formed, write valid formulas for compounds that would result by
combining the different ions if they would switch partners. Then write the formulas as products in
the equation and indicate the state of matter (s for insoluble products and aq for soluble products).
Ba2+ would combine with SO42 to form BaSO4
Na+ would combine with NO3 to form NaNO3 not Na2(NO3)2
Ba(NO3)2(aq)
+ Na2SO4(aq)
BaSO4(s)
+ NaNO3(aq)
step 4: Balance the equation by applying appropriate coefficients in front of the compounds. Note that
when balancing these types of equations, it is easier to treat the polyatomic ions as a group.
Ba(NO3)2(aq)
+ Na2SO4(aq)
BaSO4(s)
+ 2NaNO3(aq)
step 5: Write the complete ionic equation by showing any soluble ionic compounds as dissociated ions
in solution.
Ba2+(aq)
+ 2NO3 (aq)
+ 2Na+(aq)
+ SO42 (aq)
BaSO4(s)
+ 2Na+(aq)
+ 2NO3 (aq)
step 6: Write the net ionic equation by eliminating any spectator ions. Note that the net ionic equation is
simply an abbreviated form of the complete ionic equations. No new chemicals should appear.
Ba2+(aq)
+ SO42 (aq)
BaSO4(s)
In order to avoid mistakes, keep the following points in mind.
1) When balancing an equation, the equation should be balanced in terms of both charge and mass. The
net charge on the left side of the equation should match the net charge on the right side of the
equation.
2) If a compound formula has more than one of either a monatomic or polyatomic ion, a subscript is
used in the formula to indicate how many of each ion are used. When the compound dissociates in
water, a coefficient is used in front of the formula to indicate the number of ions.
Ba(NO3)2 leads to 2NO3 not (NO3 )2
Na2SO4 leads to 2Na+ not Na2+
3) Avoid parentheses around polyatomic ions unless the ions are in compound formulas.
use 2NO3 not 2(NO3 )