Precipitation
Reactions
Precipitation Reactions
Precipitation reactions are reactions in which a
solid forms when we mix two solutions.
1) reactions between aqueous solutions of ionic compounds
2) produce an ionic compound that is insoluble in water
3) The insoluble product is called a precipitate.
Precipitation Reactions
2 NaI(aq) + Pb(NO3)2(aq) ➜ PbI2(s) + 2 NaNO3(aq)
What does it mean when a substance is soluble?
Solubility Rules
Compounds Containing the
Following Ions Are Mostly Soluble
Li+, Na+, K+, NH4+
NO -, C H O -, ClO 3
2
3
2
4
Exceptions
None
None
Cl- , Br- , ISO 2-
Ca2+, Sr2+, Ba2+,Pb2+
Compounds Containing the
Following Ions Are Mostly Insoluble
Exceptions
4
Ag+, Hg22+, Cu+, Pb2+
OHS2-
Group I cations, Ca2+, Sr2+, Ba2+, NH4+
CO32-, PO43-
Group I cations, NH4+
Group I cations, Ca2+, Sr2+, Ba2+
2 NaI(aq) + Pb(NO3)2(aq)
➜ PbI2(s) + 2 NaNO3(aq)
No Precipitate Formation = No Reaction
KI(aq) + NaCl(aq) ➜ KCl(aq) + NaI(aq)
all ions still present, therefore, no reaction
KI(aq)
KCl(aq) + NaI(aq)
NaCl(aq)
Process for Predicting the Products of
a Precipitation Reaction
1.
Determine which ions are present in each aqueous reactant.
2.
Determine formulas of possible products.
3.
Determine solubility of each potential product in water.
4.
If neither product will precipitate, write no reaction after the
arrow.
5.
If any of the possible products are insoluble, write their formulas as
the products of the reaction using (s) after the formula to indicate
solid. Write any soluble products with (aq) after the formula to
indicate aqueous.
6.
Balance the equation.
Remember to only change coefficients, not subscripts
Practice – Predict the products and balance the equation:
K2CO3(aq) + NiCl2(aq) ➜
K2CO3(aq) + NiCl2(aq) ➜
KCl (?) + NiCO3(?)
K2CO3(aq) + NiCl2(aq) ➜ 2 KCl (?) + NiCO3(?)
K2CO3(aq) + NiCl2(aq) ➜ 2 KCl (aq) + NiCO3(s)
Practice – Predict the products and balance the equation:
KCl(aq) + AgNO3(aq) ➜
KCl(aq) + AgNO3(aq) ➜ KNO3(?) + AgCl(?)
KCl(aq) + AgNO3(aq) ➜ KNO3(aq) + AgCl(s)
Practice – Predict the products and balance the equation:
Na2S(aq) + CaCl2(aq) ➜
Na2S(aq) + CaCl2(aq) ➜ NaCl(?) + CaS(?)
Na2S(aq) + CaCl2(aq) ➜ 2 NaCl(?) + CaS(?)
Na2S(aq) + CaCl2(aq) ➜ 2 NaCl(aq) + CaS(aq)
No Reaction !!!!!
Practice – Predict the products and balance the equation:
(NH4)2SO4(aq) + Pb(C2H3O2)2(aq) ➜
(NH4)2SO4(aq) + Pb(C2H3O2)2(aq) ➜ NH4C2H3O2(?) + PbSO4(?)
(NH4)2SO4(aq) + Pb(C2H3O2)2(aq) ➜ 2 NH4C2H3O2(?) + PbSO4(?)
(NH4)2SO4(aq) + Pb(C2H3O2)2(aq) ➜ 2 NH4C2H3O2(aq) + PbSO4(s)
Ionic Equations
Equations that describe the chemicals put into the water and
the product molecules are called molecular equations.
2 KOH(aq) + Mg(NO3)2(aq) ➜ 2 KNO3(aq) + Mg(OH)2(s)
Equations that describe the material’s structure when
dissolved are called complete ionic equations.
Aqueous strong electrolytes are written as ions.
Insoluble substances, weak electrolytes, and nonelectrolytes are
written as molecules.
Ionic Equations
Equations that describe the chemicals put into the water and
the product molecules are called molecular equations.
2 KOH(aq) + Mg(NO3)2(aq) ➜ 2 KNO3(aq) + Mg(OH)2(s)
Equations that describe the material’s structure when
dissolved are called complete ionic equations.
Aqueous strong electrolytes soluble ionic compounds
strong acids and bases
Nonelectrolytes
insoluble ionic compounds
weak acids and bases
new molecular compounds
2K+(aq) + 2OH−(aq) + Mg2+(aq) + 2NO3−(aq) ➜ 2K+(aq) + 2NO3−(aq) + Mg(OH)2(s)
Ionic Equations
Equations that describe the chemicals put into the water and
the product molecules are called molecular equations.
2 KOH(aq) + Mg(NO3)2(aq) ➜ 2 KNO3(aq) + Mg(OH)2(s)
2K+(aq) + 2OH−(aq) + Mg2+(aq) + 2NO3−(aq) ➜ 2K+(aq) + 2NO3−(aq) + Mg(OH)2(s)
Ionic Equations
Ions that are both reactants and products are called spectator ions.
2 K+(aq) + 2 OH−(aq) + Mg2+(aq) + 2 NO3−(aq) ➜ 2 K+(aq) + 2 NO3−(aq) + Mg(OH)2(s)
An ionic equation in which the spectator ions are removed is called a
net ionic equation.
2 OH−(aq) + Mg2+(aq) ➜ Mg(OH)2(s)
Write the ionic and net ionic equation
K2SO4(aq) + 2 AgNO3(aq) ➜ 2 KNO3(aq) + Ag2SO4(s)
2K+ (aq) + SO42-(aq) + 2Ag+ (aq) + 2NO3-(aq) ➜ 2K+ (aq) + 2NO3-(aq) + Ag2SO4(s)
2
Ag+(aq)
+ SO4
2−(aq)
➜ Ag2SO4(s)
Acids and Bases
Acids and Bases in Solution
Acids “ionize” in water to form H+ ions.
(More precisely, the H+ from the acid molecule is
donated to a water molecule to form hydronium
ion, H3O+)
Bases “dissociate” in water to form OH- ions.
(Bases, such as NH3, that do not contain OH- ions,
produce OH- by pulling H+ off water molecules.)
acid + base ➜ salt + water
Molecular Models of Selected Acids
Acid-Base Reactions
Also called neutralization reactions because the
acid and base neutralize each other’s properties
2 HNO3(aq) + Ca(OH)2(aq) ➜ Ca(NO3)2(aq) + 2 H2O(l)
Note that the cation from the base combines with the
anion from the acid to make the water soluble salt.
The net ionic equation for an acid-base reaction is
2 H+(aq) + 2 OH-(aq) ➜ 2 H2O(l)
acid + base ➜ a salt + water
Common Acids
Name
Formula
Uses
Strength
Perchloric
HClO4
explosives, catalysts
Strong
Nitric
HNO3
explosives, fertilizers, dyes, glues
Strong
Sulfuric
H2SO4
Strong
Hydrochloric
HCl
Phosphoric
H3PO4
explosives, fertilizers, dyes, glue,
batteries
metal cleaning, food prep, ore
refining, stomach acid
fertilizers, plastics, food
preservation
Chloric
HClO3
explosives
Moderate
Acetic
HC2H3O2
plastics, food preservation,
vinegar
Weak
Hydrofluoric
HF
metal cleaning, glass etching
Weak
Carbonic
H2CO3
soda water, blood buffer
Weak
Hypochlorous
HClO
sanitizer
Weak
Boric
H3BO3
eye wash
Weak
Strong
Moderate
Common Bases
Name
Formula
Common Name
Uses
Strength
Sodium
Hydroxide
NaOH
Lye, Caustic Soda
soap, plastic production,
petroleum refining
Strong
Potassium
Hydroxide
KOH
Caustic Potash
soap, cotton processing,
electroplating
Strong
Calcium
Hydroxide
Ca(OH)2
Slaked Lime
cement
Strong
Sodium
Bicarbonate
NaHCO3
Baking Soda
food preparation, antacids
Weak
Magnesium
Hydroxide
Mg(OH)2
Milk of Magnesia
antacids
Weak
Ammonium
Hydroxide
NH4OH
Ammonia Water
fertilizers, detergents,
explosives
Weak
HCl(aq) + NaOH(aq) ➜ NaCl(aq) + H2O(l)
HCl(aq)
NaOH(aq)
NaCl(aq) +
H2O(l)
Write the molecular, ionic, and net-ionic
equation for the acid-base reactions .
HNO3(aq) + Ca(OH)2(aq) ➜
HNO3(aq) + Ca(OH)2(aq) ➜ Ca(NO3)2(aq) + H2O(l)
2HNO3(aq) + Ca(OH)2(aq) ➜ Ca(NO3)2(aq) + 2H2O(l)
2H+ (aq) + 2NO3-(aq) + Ca2+ (aq) + 2OH-(aq) ➜ Ca2+ (aq) + 2NO3-(aq) + 2H2O(l)
2H+(aq) + 2OH-(aq) ➜ 2H2O(l)
HCl(aq) + Ba(OH)2(aq) ➜
2HCl(aq) + Ba(OH)2(aq) ➜ BaCl2(aq) + 2H2O(l)
2H+(aq) + 2OH-(aq) ➜ 2H2O(l)
Write the molecular, ionic, and net-ionic
equation for the acid-base reactions .
H2SO4(aq) + Sr(OH)2(aq) ➜
H2SO4(aq) + Sr(OH)2(aq) ➜ SrSO4(s) + 2 H2O(l)
2H+ (aq) + SO42-(aq) + Sr2+ (aq) + 2OH-(aq) ➜ SrSO4 (s) + 2H2O(l)
2H+(aq) + SO42-(aq) + Sr2+ (aq) + 2OH-(aq) ➜ SrSO4 (s) + 2H2O(l)
Gas-Evolving
Reactions
Gas-Evolving Reactions
Some reactions form a gas directly from the ion exchange:
K2S(aq) + H2SO4(aq) ➜ K2SO4(aq) + H2S(g)
Other reactions form a gas by the decomposition of one
of the ion exchange products into a gas and water.
K2SO3(aq) + H2SO4(aq) ➜ K2SO4(aq) + H2SO3(aq)
H2SO3 ➜ H2O(l) + SO2(g)
Gas-Evolving Reactions
NaHCO3(aq) + HCl(aq) ➜ NaCl(aq) + CO2(g) + H2O(l)
NaHCO3(aq)
NaCl(aq) + CO2(g)
+ H2O(l)
HCl(aq)
A reaction which forms a gas by the decomposition of
one of the ion exchange products into a gas and water.
NaHCO3(aq) + HCl(aq) ➜ NaCl(aq) + H2CO3(aq)
H2CO3 ➜ H2O(l) + CO2(g)
“carbonic
acid”
Practice – Write the ionic and net ionic equation for
Na2CO3(aq) + 2 HCl(aq) ➜ 2 NaCl(aq) + CO2(g) + H2O(l)
2Na+ (aq) + CO32-(aq) + 2H+ (aq) + 2Cl-(aq) ➜ 2Na+ (aq) + 2Cl-(aq) + CO2(g) + H2O(l)
CO3
2−(aq)
+ 2 H+(aq) ➜ CO2(g) + H2O(l)
Compounds that Undergo
Gas-Evolving Reactions
Reactant
Reactant
Exchange
Product
Gas
Formed
Metal sulfide
Metal hydrogensulfide
Acid
H2S
H2S
K2S (g) + HCl (aq)→
H2S (g) + KCl (aq)
Metal carbonate
Metal hydrogencarbonate
Acid
H2CO3
CO2
K2CO3 (aq) + HCl (aq) → CO2
(g) + H2O (l) + KCl (aq)
Metal sulfite
Metal hydrogensulfite
Acid
H2SO3
SO2
K2SO3 (aq) + HCl (aq) →
SO2 (g) + H2O (l) + KCl (aq)
Ammonium salt
Base
NH4OH
NH3
KOH (aq) + NH4Cl (aq) →
NH3 (g) + H2O (l) + KCl (aq)
Example
Practice – Predict the products and
balance the equations
Na2CO3(aq) + 2 HNO3(aq) ➜
2 NaNO3(aq) + H2O (l) + CO2(g)
2 HCl(aq) + Na2SO3(aq) ➜
2 NaCl (aq) + H2O (l) + SO2 (g)
H2SO4(aq) + CaS(aq) ➜
CaSO4(aq) + H2S(g)
Redox Reactions
Oxidation/Reduction Basic Definitions
eX
Y
X loses electrons
Y gains electron
X is oxidized
Y is reduced
X is the reducing
agent
Y is the oxidizing
agent
X increases its
oxidation number
Y decreases its
oxidation number
Oxidation and Reduction at the Atomic Level
Redox Reactions
Oxidation/reduction reactions involve transferring
electrons from one atom to another.
Also known as redox reactions
Many involve the reaction of a substance with O2(g).
4 Fe(s) + 3 O2(g) ➜ 2 Fe2O3(s)
“ Fe0 +
O0
Fe+3
+
O-2 ”
Combustion as Redox
2 H2(g) + O2(g) ➜ 2 H2O(g)
“ H0 +
O0
H+1
+
O-2 ”
Redox without Combustion
2 Na(s) + Cl2(g) ➜ 2 NaCl(s)
“ Cl0 +
Na0
Cl-1
+
Na+1 ”
Reactions of Metals with Nonmetals
Consider the following reactions:
4 Na(s) + O2(g) → 2 Na2O(s)
2 Na(s) + Cl2(g) → 2 NaCl(s)
The reactions involve a metal reacting with a nonmetal.
In addition, both reactions involve the conversion of free
elements into ions.
Na2O = 2 Na+ + O2NaCl = Na+ + Cl-
Oxidation–Reduction
Oxidation and reduction must
occur simultaneously.
2 Na(s) + Cl2(g) → 2 Na+Cl–(s)
Na is oxidized
Cl is reduced
Na is the reducing agent
Cl2 is the oxidizing agent
Another Spontaneous Redox Reaction
governed by the
“activity series”
Zn0 +
CuSO4
Zn0 + Cu2+
Cu0
+
ZnSO4
Zn2+ + Cu0
Zn0 + Cu2+
Zn2+ + Cu0
electrons
Zn2+ NO3-
NO3-
Cu2+
A Voltaic Cell