Chemistry
Name:
§08.02B
Date:
Precipitation Reactions (and Solubility)
Task
Your tasks in this activity are to predict some double replacement reactions and observe them in
the lab.
Background
Chemistry is based on chemical reactions. General indications that a reaction has occurred are
the production of (1) a gas, (2) energy (e.g., heat), (3) water, and/or (4) a precipitate. A precipitate
is an insoluble product of a chemical reaction that separates from the solution. Examples in
daily life are rain and snow. In the lab, because we use water, precipitates are solids.
The most common type of chemical reaction in which a precipitate is formed is a double
replacement reaction. In this type of reaction, two ionic compounds rearrange to form two new
substances. The schematic for a double replacement reaction is:
AB + CD  AD + CB
Where A and C are cations and B and D are anions.
Double replacement reactions begin with the dissolution of each ionic compound into its
separate ions. For example:
Pb(NO3)2  Pb2+(aq) + 2NO3–(aq)
and
KI

K+(aq)
+
I–(aq)
If the resulting ions do not combine, there is no reaction and the ions remain floating in
solution. However, if a precipitate is formed, those ions are removed from solution until no
more precipitate can be formed. In the above example,
Pb(NO3)2(aq) + 2KI(aq)  PbI2(s) + 2KNO3(aq)
(ionic equation)
Solubility Rules for Some Common Ionic Compounds
Soluble Compounds
Insoluble Exceptions
Li+, Na+, K+, etc.
alkali metals
NH4+
ammonium
(none)
nitrates
halides
NO3–
F–, Cl–, Br–, I–
SO42–
sulfates
Insoluble Compounds
silver (Ag+), lead (Pb2+)
silver, strontium, calcium, lead
Soluble Exceptions
carbonates
CO32–
alkali metals, etc.
phosphates
PO43–
alkali metals, etc.
hydroxides
OH–
barium (Ba2+), alkali metals, etc.
Document1 saved:2/9/2016 10:47:00 PM
Ag+, Sr2+, Ca2+, Pb2+
Chemistry
Activity – Insoluble Products of a Double Replacement Reaction
p. 2
Model
1. Write the word equation for the reactant side:
lead(II) nitrate + potassium iodide 
2. Predict the products by switching anions.
lead(II) nitrate + potassium iodide  lead(II) iodide + potassium nitrate
3. Determine if any of the products is insoluble in an aqueous solution.
(N.B. Look at the anions: You can see that the solubility table generalizes from the anions.)
a. halides are generally soluble except silver (Ag+) and lead(II) (Pb2+)
 lead(II) iodide is a precipitate ()
b. potassium nitrate: all nitrates are soluble and stay as the ions
 potassium nitrate (aq)
4. Because a precipitate was formed, the reaction does happen. If no precipitate is formed, there’s no
reaction and you can simply write ‘NR’.
5. If the reaction occurs, write the formulas for all of the chemicals and balance the equation.
1Pb(NO3)2 + 2KI  1Pb(NO3)2 + 2KI
6. Add the state symbols to the balanced chemical equation.
1Pb(NO3)2(aq) + 2KI(aq)  1PbI2() + 2KNO3(aq)
Problems 1 – Predicting Substance Solubility
A. Predict if each of the following substances is soluble (aq). If it is soluble, write the
dissociation equation. Provide an explanation for each of your answers.
1. sodium nitrate
NaNO3(s)  Na+(aq) + NO3–(aq)
(all compounds containing either alkali metals or nitrates are soluble)
2. potassium hydroxide
3. ammonium hydroxide
4. sodium fluoride
5. strontium hydroxide
6. iron(II) bromide
7. calcium phosphate
8. silver(I) nitrate
9. ammonium phosphate
10. magnesium chloride
Problems 2 – Predicting if a precipitate will form in a reaction.
B. For each pair of reactants, predict if a precipitate will form. If no reaction occurs, write ‘NR’.
If a precipitate is formed, write the balanced chemical equation with the state symbols.
11. sodium hydroxide(aq) + potassium carbonate(aq) 
12. sodium hydroxide(aq) + iron(III) chloride(aq) 
13. magnesium chloride(aq) + silver(I) nitrate (aq) 
14. barium chloride(aq) + sodium hydroxide (aq) 
15. sodium sulfate(aq) + calcium nitrate(aq) 
Chemistry
Activity – Insoluble Products of a Double Replacement Reaction
p. 3
KEY:
Problems 1 – Predicting Substance Solubility
A. Predict if each of the following substances is soluble (aq). If it is soluble, write the
dissociation equation. Provide an explanation for each of your answers.
NaNO3(s)  Na+(aq) + NO3–(aq)
(all compounds containing either alkali metals or nitrates are soluble)
1. sodium nitrate
K+ is always soluble
2. potassium hydroxide
NH4+ is always soluble
3. ammonium hydroxide
Na+ is always soluble
4. sodium fluoride
insoluble (OH– + alkaline earth)
5. strontium hydroxide
Br– soluble (not Pb or Ag)
6. iron(II) bromide
7.
8.
9.
10.
insoluble (PO43-)
nitrate is always soluble
ammonia is always soluble
soluble (Cl only insoluble with Ag & Pb)
calcium phosphate
silver(I) nitrate
ammonium phosphate
magnesium chloride
Problems 2 – Predicting if a precipitate will form in a reaction.
B. For each pair of reactants, predict if a precipitate will form. If no reaction occurs, write ‘NR’.
If a precipitate is formed, write the balanced chemical equation with the state symbols.
11. sodium hydroxide(aq) + potassium carbonate(aq) 
sodium carbonate(aq) + potassium hydroxide(aq)
both products contain alkali metals, so no precipitate, gas, or water is formed
sodium hydroxide(aq) + potassium carbonate(aq)  no reaction
12. sodium hydroxide(aq) + iron(III) chloride(aq) 
sodium chloride(aq) + iron(III) hydroxide()
hydroxides are generally insoluble; iron is not an exception
3NaOH(aq) + 1FeCl3(aq)  3NaCl(aq) + 1Fe(OH)3()
13. magnesium chloride(aq) + silver(I) nitrate (aq) 
magnesium nitrate(aq) + silver chloride()
nitrate is insoluble; halides are generally soluble but silver (and lead) is an exception
1MgCl2(aq) + 2AgNO3(aq)  1Mg(NO3)2(aq) + 2AgCl()
14. barium chloride(aq) + sodium hydroxide (aq) 
barium hydroxide(aq) + sodium chloride(aq)
hydroxides are generally insoluble but barium is an exception; sodium is an alkali metal
barium chloride(aq) + sodium hydroxide (aq)  no reaction
15. sodium sulfate(aq) + calcium nitrate(aq) 
sodium nitrate(aq) + calcium sulfate (aq)
hydroxides are generally insoluble but barium is an exception;
sulfates are generally soluble but calcium is an exception
2Na2SO4(aq) + 1Ca(NO3)2(aq)  2NaNO3(aq) + 1CaSO4()