Experiment 24
“Solubility Rules”
Objectives:
● Observe and Record chemical changes that form precipitates.
● Derive general solubility rules from experimental data.
● Describe precipitation reactions by writing net ionic equations.
Introduction:
In the study of chemical reactions it is helpful to have an idea of which compounds can be expected to forms precipitates. A soluble compound will dissolve readily in water and, therefore, will not form a precipitate. An insoluble compound will not dissolve readily in water and, therefore, will form a precipitate.
How do we know which ionic compounds form precipitates and which do not? We can make a large number of mixings involving many different cations and anions. By observing the results and correlating them in a logical fashion, we can formulate some general solubility rules based on the formation of precipitates.
These guidelines can be used to describe the behavior of ionic compounds in solution and to determine which compounds form precipitates. For example, if a sodium ion is used as a probe and a large number of observations indicate that no precipitates containing the sodium ion are formed in aqueous solution, one conclusion might be: “All sodium salts are soluble in water. They do not form precipitates.” In fact, a large number of such observations have been made, and it is well known that all sodium salts are water-soluble and that there are no common exceptions to this rule.
Purpose:
In this lab you will carry out an experiment from whose data you can derive some general solubility guidelines or rules. You will do this by mixing a number of cation solutions and anion solutions two by two. Each anion solution will be used as a probe to determine which cations form precipitates with that anion.
Careful selection of compounds to represent cations and anions is important. For example, the solutions to represent anions are chosen to be compounds of sodium because we know that all sodium compounds are soluble in water, so any precipitate we see will be typical
+
of the anion. Sodium ion, Na
, will always be a “spectator ion” and will not take part in any chemical reaction. Keep in mind that you need not perform mixings between solutions having a common ion. For example, it should be obvious that CuSO will not react with Na
SO
4
2
4 because

both compounds contain the sulfate ion. Thus, with a little planning you can avoid any unnecessary mixings.
Procedure:
On top of the experimental page, mix two drops of each corresponding location and record observations in composition book.
Data:
Anions:
Cations:
AlCl
3
3+
(Al
)
NH
Cl
4
+
(NH
)
4
CaCl
2
2+
(Ca
)
CuSO
4
2+
(Cu
)
NaCl
+
(Na
)
FeCl
3
3+
(Fe
)
Pb(NO
)
3
2
2+
(Pb
)
MgSO
4
2
(Mg
)
KI
+
(K
)
AgNO
3
+
(Ag
)
ZnCl
2
2+
(Zn
)

Na
CO
2
3
2-
(CO
)
3

NaCl
-
(Cl
)

NaOH
-
(OH
)

NaNO
3
3-
(NO
)

Na
PO
3
4
3-
(PO
)
4

Na
SO
2
4
2-
(SO
)
4

Now it’s Your Turn:
1. Repeat the reaction between the silver nitrate, AgNO
, and sodium hydroxide, NaOH.
3
This mixture produces water, sodium nitrate, and silver oxide rather than silver hydroxide. Write and balance a chemical equation to describe this reaction. What is the distinctive color of silver oxide?
2. Repeat the reaction between calcium chloride, CaCl sodium sulfate, Na
SO
. Write
2, and 2
4
and balance a chemical equation to describe this reaction. What is distinctive about this reaction? 3. Repeat the reaction between aluminum chloride, AlCl
, and sodium hydroxide, NaOH.
3
Write and balance a chemical equation to describe this reaction. Now add several more drops of NaOH. What is distinctive about this reaction?
4. Repeat the reaction between zinc chloride, ZnCl
, and sodium hydroxide, NaOH. Write
2
and balance a chemical equation to describe this reaction. Now add several more drops of NaOH. What is distinctive about this reaction?
5. Repeat the reaction between lead (II) nitrate, Pb(NO
)
,