REACTIONS BETWEEN IONS - DOC

							                                                                                          Exp. 30, p. 1

                               REACTIONS BETWEEN IONS
                                IN AQUEOUS SOLUTIONS

Purpose:

        In this experiment you will combine solutions of different ionic substances which dissolve in
water to see if an insoluble substance will form. The insoluble substance will precipitate from the so-
lution. From the combinations of ions that you start with, you will try to deduce the formula of the in-
soluble precipitate. Once you know its formula, you will be able to write a net ionic equation for the
reaction.

Theory:

        Many ionic compounds, like NaCl or Pb(NO3)2, dissolve readily in water. When these com-
pounds dissolve the positive and negative ions separate from each other. Each ion becomes sur-
rounded by water molecules and moves independently through the solution. However, there are also
many other ionic compounds, like PbCl2, which hardly dissolve at all. If a solution of NaCl is mixed
with a solution of Pb(NO3)2, the Pb2+ ions will combine with the Cl ions to form the insoluble preci-
pitate, PbCl2. The Na+ ions and the NO3 ions will remain in solution.

       We can write an equation to show reactions such as this. A "molecular" equation would be:

                     2 NaCl(aq) + Pb(NO3)2(aq)  PbCl2(s) + 2 NaNO3(aq)

       Here the symbol "aq" means aqueous, and "s" means the formation of a solid.

       Since the solutions really contain independent ions, a more proper equation would be an ionic
equation:

        2 Na+(aq) + 2 Cl(aq) + Pb2+(aq) + 2 NO3(aq)  PbCl2(s) + 2 Na+(aq) + 2 NO3(aq)

        In this equation you can see that the Na+ ions and the NO3 ions do not really react. They are
called "spectator" ions. An equation that shows only the substances that take part in the reaction is
called a "net ionic equation". In a net ionic equation, spectator ions are not included:

                                  Pb2+(aq) + 2 Cl(aq)  PbCl2(s)

       Notice that in a net ionic equation both atoms and charges must balance.

Equipment:

       Glass plates or plastic sheets

Chemicals:

       Sets of chemical solutions:
                                                                                            Exp. 30, p. 2

       Set 1:          Set 2:         Set 3:          Set 4:          Set 5:
       Ba(NO3)2        Na2SO4         FeCl3           Co(NO3)2        BaCl2
       BaCl2           Al2(SO4)3      Co(NO3)2        MgCl2           Sr(NO3)2
       K2CO3           Sr(NO3)2       CoCl2           Na2SO4          Na2CO3
       Na2CO3          BaCl2          NaOH            NaOH            Al2(SO4)3
       NaNO3           Ba(NO3)2       KOH             Ba(OH)2         K2CO3
       SrCl2           AlCl3          NaNO3           MgSO4           AgNO3

Procedure:


 SAFETY PROCEDURE
       Compounds that contain the OH ion are bases and are hazardous to skin and eyes. Use
 them carefully. Many of the compounds are poisons. If you spill a compound on yourself, wash it
 off with lots of water. Wash your hands before you leave the lab.
       Wear your safety goggles and apron.


        On a glass plate place two drops of one of the chemical solutions from a set. Place two drops
of a second solution from the set on top of the first one. Be careful not to touch the droppers to the so-
lutions on the plate. Observe if a reaction occurs, and note the color of any precipitates. Repeat with
all possible combinations of the solutions in a set. Carry out experiments with as many sets as your
teacher directs.

       For each combination where a precipitate appears, figure out which combination of ions is re-
sponsible for the precipitate. The table of solubility rules will help you with this, and you can also
compare data from different combinations in a set to find similar precipitates.

       Write a molecular equation, an ionic equation, and a net ionic equation for each reaction that
took place.

SOLUBILITY RULES

1. Salts of the alkali metals (Li+, Na+, K+, etc.) are soluble.
2. Ammonium (NH4+) salts are soluble.
3. Salts containing nitrate (NO3), perchlorate (ClO4), and acetate (C2H3O2) are soluble.
4. All chlorides (Cl), bromides (Br), and iodides (I) are soluble EXCEPT for those of Pb2+, Hg22+,
and Ag+ which are insoluble.
5. All sulfates (SO42) are soluble EXCEPT for those of Sr2+, Ba2+, Hg22+, Hg2+, and Pb2+ which are
insoluble. The sulfate salts of Ca2+ and Ag+ are moderately soluble.
6. All hydroxides (OH) are insoluble EXCEPT for those of the alkali metals, which are soluble, and
the hydroxides of Ca2+, Ba2+ and Sr2+ which are moderately soluble.
7. All sulfites (SO32), carbonates (CO32), chromates (CrO42), and phosphates (PO43), are insoluble
EXCEPT for those of NH4+ and the alkali metals, which are soluble.
8. All sulfides (S2) are insoluble except for those of NH4+, the alkali metals, and the alkaline earths,
which are soluble.
                                                                                        Exp. 30, p. 3

                                REACTIONS BETWEEN IONS
                                 IN AQUEOUS SOLUTIONS

Name _________________________________ Date _________________ Class _______________

Record your observations in the tables which follow. Use the solubility rules and evidence from the
table to determine the formulas of the precipitates. Write a molecular equation, ionic equation, and
net ionic equation for each reaction that takes place.
        Note that it is not necessary to fill in the shaded blocks. Why?



SET 1:
                     Ba(NO3)2    BaCl2      K2CO3       Na2CO3      NaNO3       SrCl2
         Ba(NO3)2
         BaCl2
         K2CO3
         Na2CO3
         NaNO3
         SrCl2


SET 2:

                     Na2SO4      Al2(SO4)3 Sr(NO3)2     BaCl2       Ba(NO3)2    AlCl3
         Na2SO4
         Al2(SO4)3
         Sr(NO3)2
         BaCl2
         Ba(NO3)2
         AlCl3


SET 3:

                     FeCl3       Co(NO3)2 CoCl2         NaOH        KOH         NaNO3
         FeCl3
         Co(NO3)2
         CoCl2
         NaOH
         KOH
         NaNO3
                                                                         Exp. 30, p. 4

SET 4:

                     Co(NO3)2 MgCl2      Na2SO4   NaOH     Ba(OH)2   MgSO4
         Co(NO3)2
         MgCl2
         Na2SO4
         NaOH
         Ba(OH)2
         MgSO4


SET 5:

                     BaCl2    Sr(NO3)2   Na2CO3   Al2(SO4)3 K2CO3    AgNO3
         BaCl2
         Sr(NO3)2
         Na2CO3
         Al2(SO4)3
         K2CO3
         AgNO3