3.4 Double Displacement
Reactions
Double Displacement Reactions
• Double Displacement Reactions occur when a
metal replaces a metal in a compound and a nonmetal
replaces a nonmetal in a compound
• Compound + compound  product + product
• AB + CD  AD + CB
Double Displacement Reactions
• Think about it like “foil”ing in algebra, first and last ions
go together + inside ions go together
• Example:
AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq)
• Another example:
K2SO4(aq) + Ba(NO3)2(aq) 2 KNO3(aq) + BaSO4(s)
Solubility of D.D. Products
 A property of a substance that describes it’s




ability to dissolve in another substance at a
given temperature and pressure
The solute is the substance that is dissolved
The solvent is the medium in which the solute
dissolves
If the product of a reaction is very soluble and
will stay in solution it may be given the
subscript (aq)
A product that is insoluble is given the
subscript (s) or (g) depending on it’s state
when produced

A solid, undissolved product is a precipitate
Solubility Predictions
 Use Table 1 p. 173 to predict whether an ionic
compound, formed as the product of a chemical
redaction in solution, is likely to form a precipitate
(not soluble) or form a solution (soluble)
 If both possible products are highly soluble, write
“no reaction”
Practice
•
1.
2.
3.
4.
5.
6.
Predict the products. Balance the equation
HCl(aq) + AgNO3(aq)  HNO3(aq) + AgCl(s)
3CaCl
2(aq) + 2Na3PO4(aq)  Ca3(PO4)2(s) + 6NaCl(aq)
Pb(NO3)2(aq) + BaCl2(aq)  PbCl2(s) + Ba(NO3)2(aq)
FeCl3(aq) + 3 NaOH(aq)  FeOH3(s) + 3NaCl(aq)
H2SO4(aq) +2NaOH(aq)  H2O(l) + Na2SO4(aq)
2KOH(aq) + CuSO4(aq)  Cu(OH)2(s) + K2SO4(aq)
Types of Double Displacement Reactions
 Precipitate Reactions – one of the two products is an
insoluble product


The other product may remain in solution
AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)
 Reactions Producing a Gas – One of the products is a
gas which is released


Na2S(aq) + 2HCl(aq) → 2NaCl(aq) + H2S(g)
See table 2 p. 176 for more examples of gases
 Neutralization Reaction – reaction between an acid
and base where water and a salt (ionic compound)
are produced

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
Mixed Practice
•
1.
2.
3.
4.
State the type, predict the products, and balance
the following reactions:
BaCl2 + H2SO4  2HCl + BaSO4
D.D
S.D
Zn + CuSO4  ZnSO4 + Cu
2 Cs + 3 Br2  2CsBr3
Synthesis
Decomposition
FeCO3  Fe + CO
3
Homework
 Read pp. 172 – 177
 Answer p.177 # 4 – 6