Double Replacement Reactions
How do we know if these happen?
Double Replacement Reaction
2 KI(aq) + Pb(NO3)2(aq)  2 KNO3(aq) + PbI2(s)
Double Replacement Reactions
• Two types of Double Replacement Reactions:
1. Formation of an insoluble precipitate
•
NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)
2. Formation of a gas
•
•
Acid + salt → gas + another salt
H2SO4(aq) + Na2S(aq) → H2S(g) + Na2SO4(aq)
Solubility Rules
• All sodium, potassium, and ammonium salts are
soluble
• All acetate, nitrate, and chlorate salts are soluble
• All halide salts (F, Cl, Br, I) are soluble
– Except lead (II), silver, and mercury (I)
• All sulfates are soluble
– Except calcium, barium, lead (II), and silver
• All carbonates, phosphates, and sulfides are
INSOLUBLE
– Except sodium, potassium, ammonium
Ionic Equations
• Since ionic compounds (salts) exist as ions in
solution, a precipitation reaction can be
shown as ions:
– NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)
– Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq) → Na+(aq) + NO3-(aq) +AgCl(s)
• This is the ionic equation for the reaction
– Be careful with coefficients and subscripts from
balanced formula equations
Net Ionic Equations
• Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq) → Na+(aq) + NO3-(aq) +AgCl(s)
• Na+ and NO3- ions are on both side, so they can be
cancelled:
– Cl-(aq) + Ag+(aq) → AgCl(s)
• Na+ and NO3- are spectator ions
• They are soluble on both sides of the ionic equation
• The net ionic equation shows the reaction without
the spectator ions
– The net ionic equation shows which ions react and
how the reaction occurs
For the following sets of reactants…
• Predict if a reaction will occur, based on
solubility rules
• Write a balanced formula equation, if the
reaction occurs
• Write a balanced ionic equation, if the
reaction occurs
• Write a balanced net ionic equation, if the
reaction occurs
Double Replacement Reactions
1.
2.
3.
4.
5.
6.
7.
Potassium chromate + silver nitrate
Sodium hydroxide + iron (III) chloride
Sodium nitrate + calcium chloride
Lead (II) acetate + potassium sulfate
Silver nitrate + magnesium sulfate
Potassium hydroxide + nitric acid
Sodium acetate + potassium carbonate