Chemistry I
Name ______________________________________
Title: Precipitation Reactions
Purpose: To identify when a precipitation reaction will occur and to write the net ionic
reactions.
Background: A precipitation reaction is a double replacement reaction in which two
solutions containing soluble ionic compounds are combined to form a compound that is
insoluble. This insoluble ionic compound usually forms a finely divided powder or
gelatinous solid that is referred to as a precipitate. An example of a precipitation reaction
in which a solution of silver (I) nitrate is mixed with a solution of sodium chloride, to
form the precipitate silver (I) chloride and a solution of sodium nitrate is given in
Equation 1. For the soluble ionic compounds one could write the reaction in a form that
describes the ions that are present in solution, as shown in Equation 2. The ionic solid is
not broken into its component ions in this type of reaction. Note that some of the ions,
e.g. in this case the sodium and nitrate ions, appear to be unchanged as a result of the
reaction. These ions are referred to as spectator ions. Removing the spectator ions from
the ionic reaction, produces the net ionic reaction, as shown in Equation 3. For any given
precipitation reaction, the identity of the precipitate can be determined by using the
solubility rules, Table 1. The precipitate will always be insoluble in water.
AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)
(1)
Ag (aq) + NO3- (aq) + Na+ (aq) + Cl- (aq)  AgCl (s) + Na+ (aq) + NO3- (aq) (2)
Ag (aq) + Cl- (aq)  AgCl (s)
(2)
Table 1. Solubility Guidelines for ionic compounds in aqueous solution
Ions that form
soluble compounds
Group 1 ions (Na+,
K+, etc.)
Ammonium ion
(NH4+)
Nitrate (NO3-)
Exceptions
Ions that form
insoluble
compounds
Carbonate (CO32-)
Chromate (CrO42-)
Phosphate (PO43-)
Halides (Cl-, Br- and Ag+, Pb2+ or Hg22+
Sulfide (S2-)
I)
Sulfates (SO42-)
Ag+, Sr2+, Ba2+, Pb2+ Hydroxides (OH-)
and oxides (O2-)
© 2005 Van Der Sluys
Exceptions
Group 1 ions and
ammonium ion
Group 1 ions and
ammonium ion
Group 1 ions and
ammonium ion
Group 1 ions and
ammonium ion
Group 1 ions and
ammonium ion
Chemistry I
Name ______________________________________
Materials: Aqueous solution of ten different compounds having ions from Table 1,
plastic pipets, a plastic reaction tray.
Procedure: Place two or three drops of a solution in one of the reaction wells of the
plastic reaction tray. Add two or three drops of a second solution and mix the two
solutions. Record your observations concerning the formation of a precipitate in Table 2.
Repeat this process for all possible combinations of the ten solutions.
Data and Analysis: Record the formulas of the ionic compounds in the various solutions
in both the column and row headings of Table 2. Record your observations concerning
the formation of precipitates in the appropriate boxes, including colors of the solids.
Note that the diagonal entries represent combinations of the same solutions and will not
produce a reaction. Also note that one half of the table is identical to the other half, and
therefore will produce identical result. Only complete one half of the table. Identify the
formula of the precipitate and on a separate sheet of paper write net ionic reactions for
any combination that produces a precipitate.
Table 2. Observations concerning the formation of precipitates for various double
replacement reactions.
Formula
© 2005 Van Der Sluys