Introduces the concepts involved in predicting whether substances are soluble or insoluble. Precipitation (exchange) reactions are also discussed, along with ionic equations and net ionic equations. General Chemistry

1. Solubility of Substances in
Solution
By Shawn P. Shields, Ph.D.
This work is licensed by Shawn P. Shields-Maxwell under a Creative Commons
Attribution-NonCommercial-ShareAlike 4.0 International License.

2. Solubility
“Solubility” is defined as the amount of a given substance
that can be dissolved in a certain amount of solvent.
A “soluble
substance”
An “insoluble
substance”

3. Solubility
Substances fall into three main categories of
solubility:
Generally, a substance is considered “soluble” if it
dissolves into solution completely.
“Sparingly (or slightly) soluble” substances are partially
soluble. A limited amount of substance dissolves.
“Insoluble” substances do not dissolve at all (or a very
tiny amount dissolves.)

4. Salts
Salts are ionic compounds.
Recall that ionic compounds are composed of a metal and a
nonmetal.
Metals form cations, and nonmetals form anions.
“Salt” is another name for an ionic compound.
Salts can be soluble, sparingly soluble, and insoluble,
depending on the identity of the cation and anion.

5. Rules for Predicting Soluble Salts
Contains these
Ions Soluble Exceptions
Li+, Na+, K+,
Rb+, Cs+, NH4
+
Most salts (ionic compounds)
containing alkali metals (Group 1)
and ammonium are soluble.
none
NO3

Most salts containing nitrate are
soluble
Cl, Br, I
Most salts containing halogen
anions (Main Group 7) are soluble.
(Chloride, bromide, and iodide salts)
Salts containing Cu+, Ag+,
Pb2+, and Hg2
2+
SO4
2
Many salts containing sulfate are
soluble.
Salts containing Sr2+, Ba2+,
Pb2+, and Hg2
2+

6. Rules for Predicting Insoluble Salts
Contains these
Ions Insoluble Exceptions
OH and S2
Most salts containing hydroxide or sulfide
anions are insoluble.
Salts containing alkali metals
(Li+, Na+, K+, Rb+, and Cs+),
and the “heavy” alkaline
earth metals (Ca2+, Sr2+, and
Ba2+)
CO3
2, PO4
3
Most salts containing carbonate or
phosphate anions are insoluble.
Salts containing alkali metals
(Group 1) and ammonium
are soluble. (Li+, Na+, K+, Rb+,
Cs+, NH4
+)
SO4
2
Many salts containing sulfate and cations
with charges greater than or equal to 2
are insoluble, including salts containing
Sr2+, Ba2+, Pb2+, and Hg2
2+.
Salts containing alkali metals
(Group 1) and ammonium
are soluble. (Li+, Na+, K+, Rb+,
Cs+, NH4
+), and Mg2+

7. Is it Soluble? 
Example: Determine whether each salt given below is
soluble or insoluble, and rationalize your answer.
NaCl
BaSO4
NH4Cl

8. Is it Soluble? 
Example: Determine whether each salt given below is
soluble or insoluble, and rationalize your answer.
NaCl contains two ions that are generally found in
soluble compounds, Na+ and Cl. We predict the salt
is soluble.
BaSO4
NH4Cl

9. Is it Soluble? 
Example: Determine whether each salt given below is
soluble or insoluble, and rationalize your answer.
NaCl contains two ions that are generally found in
soluble compounds, Na+ and Cl. We predict the salt
is soluble.
BaSO4 contains sulfate, which can be either. Barium
sulfate is composed of the Ba2+ and SO4
2 ions. Salts
containing cations with 2+ charges tend to be
insoluble, so we predict this salt to be insoluble.
NH4Cl

10. Is it Soluble? 
Example: Determine whether each salt given below
is soluble or insoluble, and rationalize your answer.
NaCl contains two ions that are generally found in soluble
compounds, Na+ and Cl. We predict the salt is soluble.
BaSO4 contains sulfate, which can be either. Barium sulfate is
composed of the Ba2+ and SO4
2 ions. Salts containing cations
with 2+ charges tend to be insoluble, so we predict this salt to
be insoluble.
NH4Cl also contains two ions that are generally found in
soluble compounds, NH4
+ and Cl. We predict the salt is
soluble.

11. Precipitation Reactions
Precipitation reactions happen when
Two soluble salts are mixed
An exchange reaction occurs
And one of the salts formed is insoluble

12. Precipitation Reactions
form a solid through an exchange reaction. The ions that do
not form an insoluble solid remain dissolved in solution.
An “insoluble
substance” is formed
Soluble salts dissolve into ions
and react to form precipitate
2 soluble salts
are mixed.

13. Example Precipitation Reaction
When a solution of potassium chloride and silver nitrate are
mixed, silver chloride solid is formed.
𝐊𝐂𝐥 𝐚𝐪 + 𝐀𝐠𝐍𝐎 𝟑 𝐚𝐪 → 𝐊𝐍𝐎 𝟑 𝐚𝐪 + 𝐀𝐠𝐂𝐥 (𝐬)
So what is going on here?
Remember that the two solutions are ions dissolved in solution.
Written as a chemical equation showing all of the ions, we have
𝐊+ 𝐚𝐪 + 𝐂𝐥− 𝐚𝐪 + 𝐀𝐠+ 𝐚𝐪 + 𝐍𝐎 𝟑
−
𝐚𝐪 → 𝐊+ 𝐚𝐪 + 𝐍𝐎 𝟑
−
(𝐚𝐪) + 𝐀𝐠𝐂𝐥 (𝐬)

14. Example Precipitation Reaction
The reaction is an “exchange reaction”,
since the two salts “exchange” partners.
𝐊𝐂𝐥 𝐚𝐪 + 𝐀𝐠𝐍𝐎 𝟑 𝐚𝐪 → 𝐊𝐍𝐎 𝟑 𝐚𝐪 + 𝐀𝐠𝐂𝐥 (𝐬)
After mixing two solutions of soluble salts, exchange
the ions, then check to see if one of the products is
insoluble.
If so, a precipitate will form.

15. Spectator Ions
Notice that certain aqueous (aq) ions show up on both
sides of the equation.
These are called spectator ions.
We can cancel these out to give the “net ionic equation.”
𝐊+
𝐚𝐪 + 𝐂𝐥−
𝐚𝐪 + 𝐀𝐠+
𝐚𝐪 + 𝐍𝐎 𝟑
−
𝐚𝐪 → 𝐊+
𝐚𝐪 + 𝐍𝐎 𝟑
−
(𝐚𝐪) + 𝐀𝐠𝐂𝐥 (𝐬)
𝐂𝐥−
𝐚𝐪 + 𝐀𝐠+
𝐚𝐪 → 𝐀𝐠𝐂𝐥 (𝐬)

16. Mini Quiz
Determine whether the following reaction is a
precipitation reaction. If so, write the net ionic
equation for the reaction. Identify the spectator
ions.
Mix CaBr2 (aq) and Na2CO3(aq)

17. Mini Quiz Solution
Determine whether the following reaction is a precipitation
reaction. If so, write the net ionic equation for the reaction.
Identify the spectator ions.
Mix CaBr2 (aq) and Na2CO3(aq)
First, let’s remind ourselves that we have mixed two
soluble salts using the solubility table.
Salts containing Br are soluble, so CaBr2 is soluble.
Salts containing carbonate (CO3
2) and an alkali metal
cation (Na+) are soluble.

18. Mini Quiz Solution
Determine whether the following reaction is a precipitation reaction. If so, write
the net ionic equation for the reaction. Identify the spectator ions.
Mix CaBr2 (aq) and Na2CO3(aq)
Now, exchange the ions and check to see if an insoluble
salt is formed.
𝐂𝐚𝐁𝐫𝟐 𝐚𝐪 + 𝐍𝐚 𝟐 𝐂𝐎 𝟑 𝐚𝐪 → 𝐂𝐚𝐂𝐎 𝟑 ? ? + 𝟐 𝐍𝐚𝐁𝐫 (? ? )
Is either insoluble? (Check your table!)

19. Mini Quiz Solution
Determine whether the following reaction is a precipitation reaction. If so, write
the net ionic equation for the reaction. Identify the spectator ions.
Mix CaBr2 (aq) and Na2CO3(aq)
Now, exchange the ions and check to see if an insoluble
salt is formed.
𝐂𝐚𝐁𝐫𝟐 𝐚𝐪 + 𝐍𝐚 𝟐 𝐂𝐎 𝟑 𝐚𝐪 → 𝐂𝐚𝐂𝐎 𝟑 𝐬 + 𝟐 𝐍𝐚𝐁𝐫 (𝐚𝐪)
Is either insoluble? (Check your table!)
YES, CaCO3 is insoluble. 

20. Mini Quiz Solution
Determine whether the following reaction is a precipitation
reaction. If so, write the net ionic equation for the reaction.
Identify the spectator ions.
Mix CaBr2 (aq) and Na2CO3(aq)
Now, write out the ionic equation and cancel the
spectators.
𝐂𝐚 𝟐+
𝐚𝐪 + 𝟐 𝐁𝐫−
𝐚𝐪 + 𝟐 𝐍𝐚+
𝐚𝐪 + 𝐂𝐎 𝟑
𝟐−
𝐚𝐪 → 𝟐 𝐍𝐚+
𝐚𝐪 + 𝟐 𝐁𝐫−
(𝐚𝐪) + 𝐂𝐚𝐂𝐎 𝟑(𝐬)

21. Mini Quiz Solution
Determine whether the following reaction is a precipitation reaction. If so, write
the net ionic equation for the reaction. Identify the spectator ions.
Mix CaBr2 (aq) and Na2CO3(aq)
Now, write out the ionic equation and cancel the
spectators.
The net ionic equation is
The spectator ions are Na+ and Br.
𝐂𝐎 𝟑
𝟐−
𝐚𝐪 + 𝐂𝐚 𝟐+
𝐚𝐪 → 𝐂𝐚𝐂𝐎 𝟑 (𝐬)

22. What You Should Be Able to Do
Identify soluble and insoluble compounds using
the solubility rules provided.
Predict whether there will be a precipitate when
two solutions of soluble salts are mixed.
Identify the precipitate formed and the
spectator ions when the two solutions are
mixed (if applicable).
Write the net ionic equation for a
precipitation reaction.