2. Double Displacement Reactions

3. Double Displacement Reaction
A reaction in which aqueous ionic compounds rearrange cations (A & B) and anions (X & Y), resulting in the formation of new compounds Y X + B  A Y + X B A

4. Types of Double Displacement Reactions
A reaction that forms a solid
A reaction that forms a gas
A reaction that forms water (neutralization)

5. Determining the Products of a Double Displacement Reaction
First determine the ions that make up the reactants.
For example, consider the reaction between lithium chloride and lead(II) nitrate:
LiCl(aq) + Pb(NO3)2(aq) 

6. LiCl(aq) + Pb(NO3)2(aq)  Lithium ions, Li+ Chloride ions, Cl-
The reactants are composed of four ions:
LiCl(aq) + Pb(NO3)2(aq) 
Lithium ions, Li+
Chloride ions, Cl-
Lead(II) ions, Pb2+
Nitrate ions, NO3-

7. 2LiCl(aq) + Pb(NO3)2(aq)  2LiNO3(aq) + PbCl2(s)
To determine the products of the reaction, simply change the pairs of ions.
2LiCl(aq) + Pb(NO3)2(aq)  2LiNO3(aq) + PbCl2(s)
Lithium chloride +lead(II) nitrate
lithium nitrate + lead(II) chloride

8. MgCl2(aq) + Ca(OH)2(aq)  Mg(OH)2(s) + CaCl2(aq)
Specific Example:
MgCl2(aq) + Ca(OH)2(aq)  Mg(OH)2(s) + CaCl2(aq)
What “sign” suggests a chemical
reaction has occurred?
If there is no precipitate formed,
there is NO reaction.
How can we predict precipitate formation?

9. When will a double displacement reaction occur?
When a precipitate is produced from the reaction of 2 aqueous reactants.
To determine which products are precipitates (insoluble in water), you must check your solubility chart
When a pure liquid is formed – typically water.
When a gas is produced (often CO2, H2, and O2)
In summary any reaction where the two products are not aqueous!

10. SOLUBILITY
A solution is a homogenous mixture of a solute and a solvent
Every solute has its own solubility in a given solvent
Solubility is described as the maximum quantity of a solute that will dissolve in a solvent at a given temperature and pressure e.g. adding NaCl to water
If a product in a reaction is insoluble a precipitate will form
We use a SOLUBILITY TABLE to determine whether a precipitate will form (Nelsons Chemistry 11 p Table 1)

12. What ions can be used to precipitate the following…
Ag+
Nitrate
C2H3O2-
Ba2+
OH-
Phosphate

13. A Reaction That Forms a Solid
Precipitate Reactions CaCl2(aq) + Na2CO3(aq)  (dissolved) (dissolved) CaCO3(s) + 2 NaCl(aq) (solid precipitate) (dissolved) A precipitate is an insoluble solid that is formed by a chemical reaction between two soluble compounds

14. A Reaction That Forms a Gas
Formation of Carbon Dioxide acetic acid + sodium hydrogen carbonate  sodium acetate + carbonic acid CH3COOH(aq) + NaHCO3(s)  NaCH3COO(aq) + H2CO3(aq) NOT the overall reaction because there is NO carbon dioxide!!!

15. Carbonic acid DECOMPOSES into liquid water and carbon dioxide
H2CO3(aq)  H2O(l) + CO2(g)
OVERALL Reaction
acetic acid + sodium hydrogen carbonate 
sodium acetate + water + carbon dioxide
CH3COOH(aq) + NaHCO3(s) 
NaCH3COO(aq) + H2O(l) + CO2(g)

16. NH4Cl(aq) + NaOH(aq)  NaCl(aq) + NH4OH(aq)
Formation of Ammonia
ammonium chloride + sodium hydroxide 
sodium chloride + ammonium hydroxide
NH4Cl(aq) + NaOH(aq)  NaCl(aq) + NH4OH(aq)
NOT the overall reaction because NO ammonia!

17. Ammonium hydroxide DECOMPOSES to form water and ammonia
ammonium hydroxide  water + ammonia
NH4OH(aq)  H2O(l) + NH3(g)
OVERALL Reaction
ammonium chloride + sodium hydroxide 
sodium chloride + water + ammonia
NH4Cl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) + NH3(g)

18. A Reaction That Forms Water (Neutralization Reactions)
Acid reacts with a Base
Products are neither acidic or basic
magnesium hydroxide + hydrochloric acid 
magnesium chloride + water
Mg(OH)2(s) + 2HCl(aq)  MgCl2(aq) + 2H2O(l)

19. then the products include
Summary flowchart to help predict the products of a double displacement reaction
If one reactant… +
the other reactant… 
then the products include
is an aqueous salt
a precipitate
is an acid
has carbonate ions
water and
carbon dioxide
has ammonium ions
has hydroxide ions
water and ammonia
water

20. Assigned Questions
p. 138 # 1, 2, 3
p. 141 – 143 # 4, 5, 7, 9, 10, 11, 12