Download Classes of Chemical Reactions

Classes of Chemical Reactions
Reactions in aqueous media
• Precipitation reactions
• Acid-Base reactions
• Oxidation-Reduction reactions
• Reversible reactions
Classes of Chemical Reactions
Water (H2O), a unique solvent
most abundant liquid
medium for biochemical reactions
solvent of high polarity
O
H
H
+
Classes of Chemical Reactions
The solubility of ionic compounds: dissociation
Cl-
Na+
Cl-
Cl-
NaCl
Na
Na+
+
ClNa+
O
H
H
+
Classes of Chemical Reactions
O
H
H
+
Classes of Chemical Reactions
electrolytes: a substance that conducts an electric current
when dissolved in water
Acids are donors of H+ (this is a definition)
or
HBr ! H3O+ + Br¯
HBr ! H+ + Br¯
O
H
H
+
Equations for Aqueous Ionic
Reactions
molecular equation:
2AgNO3 + Na2CrO4 ! Ag2CrO4(s) + 2NaNO3
total ionic equation:
2Ag+ + 2NO3¯ + 2Na+ + CrO42¯ ! Ag2CrO4(s) + 2Na+ + 2NO3¯
net ionic equation:
2Ag+ + CrO42¯ ! Ag2CrO4(s)
Classes of Chemical Reactions
Precipitation Reactions
Driving Force for Precipitation Reactions:
INSOLUBILITY
Some ions combine to form insoluble products
2Al3+ + 3CO32¯ ! Al2(CO3)3 (s)
No reaction in this case:
KCl + NaBr:
K+ + Cl- + Na+ + Br- ! same ions
no precipitate
Classes of Chemical Reactions
Precipitation Reactions
Table 4.1. Solubility Principles
SOLUBLE
INSOLUBLE
1. all common compounds of Group 1A
ions and NH 4+ are soluble
1. all common metal hydroxides are
insoluble, except alkali and alkaline earth
2. all common NO3 -, CH3CO2-, and ClO4are soluble
2. all common CO32- and PO43- are insoluble,
except alkali and NH4+
3. all halides, except Ag+, Pb2+, Cu+, and
Hg22+ are soluble
3. all common sulfides (S2-) are insoluble,
except alkali
4. all common SO42- are soluble, except
Ca2+, Sr2+, Ba2+, and Pb2+
Classes of Chemical Reactions
Acid-Base Reactions
Acid - a substance that is a donor of H+:
HX ! H+ + X¯
Base - a substance that is a donor of OH¯:
MOH ! M+ + OH¯
Classes of Chemical Reactions
Acid-Base Reactions
STRONG ACIDS
WEAK ACIDS
Hydrochloric acid, HCl
Hydrofluoric acid, HF
Hydrobromic acid, HBr
Phosphoric acid, H3PO4
Hydroiodic acid, HI
Acetic acid, CH3CO2H
Nitric acid, HNO3
Carbonic acid, H2CO3
Sulfuric acid, H2SO4
Perchloric acid, HClO4
Classes of Chemical Reactions
Acid-Base Reactions
STRONG BASES
Sodium Hydroxide, NaOH
Potassium Hydroxide, KOH
WEAK BASES
Ammonia, NH3
NH3 + H2O ! NH4+ + OH¯
Calcium Hydroxide, Ca(OH)2
Strontium Hydroxide, Sr(OH)2
Barium Hydroxide, Ba(OH)2
Cesium Hydroxide, CsOH
Classes of Chemical Reactions
Acid-Base Reactions
Driving Force for Acid-Base Reactions:
FORMATION OF WATER
Ba2+ + 2OH¯ + 2H+ + 2Cl¯ ! Ba2+ + 2Cl¯ + 2H2O
Classes of Chemical Reactions
Acid-Base Reactions
Driving Force for Acid-Base Reactions:
FORMATION OF WATER
Ba2+ + 2OH¯ + 2H+ + 2Cl¯ ! Ba2+ + 2Cl¯ + 2H2O
Ba(OH)2 + 2HCl ! BaCl2 + 2H2O
Classes of Chemical Reactions
Acid-Base Reactions
Driving Force for Acid-Base Reactions:
FORMATION OF WATER
Ba2+ + 2OH¯ + 2H+ + 2Cl¯ ! Ba2+ + 2Cl¯ + 2H2O
Ba(OH)2 + 2HCl ! BaCl2 + 2H2O
OH¯ + H+ ! H2O
neutralization reaction
Classes of Chemical Reactions
Acid-Base Reactions
Acid-Base Titrations:
one solution of known concentration is used
to determine the concentration of another solution
HCl + NaOH ! NaCl + H2O
Classes of Chemical Reactions
Acid-Base Reactions
Acid-Base Titrations:
one solution of known concentration is used
to determine the concentration of another solution
HCl + NaOH ! NaCl + H2O
Acid-Base Titrations
Practice Problem
50.00 mL of an HCl solution of unknown concentration
required 33.32 ml of 0.1524 M standard NaOH solution to
reach the endpoint. What is the concentration of the HCl
solution?
Acid-Base Titrations
Practice Problem
50.00 mL of an HCl solution of unknown concentration
required 33.32 ml of 0.1524 M standard NaOH solution to
reach the endpoint. What is the concentration of the HCl
solution?
HCl + NaOH ! NaCl + H2O
Acid-Base Titrations
Practice Problem
50.00 mL of an HCl solution of unknown concentration
required 33.32 ml of 0.1524 M standard NaOH solution to
reach the endpoint. What is the concentration of the HCl
solution?
HCl + NaOH ! NaCl + H2O
n(HCl) = n(NaOH) = 0.03332 L " 0.1524 mol/L = 0.005078 mol
Acid-Base Titrations
Practice Problem
50.00 mL of an HCl solution of unknown concentration
required 33.32 ml of 0.1524 M standard NaOH solution to
reach the endpoint. What is the concentration of the HCl
solution?
HCl + NaOH ! NaCl + H2O
n(HCl) = n(NaOH) = 0.03332 L " 0.1524 mol/L = 0.005078 mol
0.005078 mol
0.05000L
= 0.1016 mol/L
Oxidation-Reduction
Red + Ox ! Products
e–
electrons
reducing agent: loses electrons
oxidizing agent: gains electrons
Oxidation-Reduction
Red + Ox ! Products
e–
electrons
reducing agent: loses electrons
oxidizing agent: gains electrons
2Mg + O2 ! 2MgO
Mg2+ O2–
Oxidation-Reduction
Red + Ox ! Products
e–
electrons
reducing agent: loses electrons
oxidizing agent: gains electrons
2Mg + O2 ! 2MgO
4 electrons
Mg2+ O2–
Oxidation-Reduction
Red + Ox ! Products
e–
electrons
reducing agent: gets oxidized
oxidizing agent: gets reduced
2Mg + O2 ! 2MgO
4 electrons
Mg2+ O2–
Oxidation-Reduction
#$
Cl
Cl
+
#+
H H
non-polar covalent bond:
electrons distributed evenly
H
Cl
polar covalent bond:
electrons distributed
unevenly
OXIDATION STATE: A MODEL, compounds treated as if
electrons were transferred completely, not actually shared.
+1
-1
H
Cl
Oxidation-Reduction
redox reactions are characterized
by change in oxidation state
H2 + Cl2 ! 2HCl
+1
-1
H
Cl
Oxidation-Reduction
redox reactions are characterized
by change in oxidation state
H2 + Cl2 ! 2HCl
reducing agent: loses electrons
oxidizing agent: gains electrons
+1
-1
H
Cl
Oxidation Number (State): General
• For an atom in its elemental form equals 0 (H2, N2)
• For monoatomic ion equals the ion charge (Ag+, S2-)
• The sum of O.N. for the atoms in a compound is zero (HCl)
• The sum of O.N. for the atoms in a polyatomic ion equals
the ion charge
ClO–
+1 -2
Oxidation Number (State): General
Rules for assigning an oxidation number
1. For Group 1A
+1 in all compounds
2. For Group 2A
+2 in all compounds
3. For hydrogen
+1 in combination with nonmetals
-1 in combination with metal
and B
4. For fluorine
-1 in all compounds
5. For oxygen
-2 in all compounds except F
and peroxides
6. For Group 7A (halogens)
-1 except with O and halogens
lower in the group
Oxidants and Reducing Agents
AgNO3 + NaCl ! AgCl(s) + NaNO3
Oxidants and Reducing Agents
-2
+1
+1 -1
+1 -1
+1
-2
AgNO3 + NaCl ! AgCl(s) + NaNO3
+5
+5
Oxidants and Reducing Agents
-2
+1
+1 -1
+1 -1
+1
-2
AgNO3 + NaCl ! AgCl(s) + NaNO3
+5
NOT a redox reaction
+5
Oxidants and Reducing Agents
-2
+1
+1 -1
+1 -1
+1
-2
AgNO3 + NaCl ! AgCl(s) + NaNO3
+5
+5
NOT a redox reaction
2Al + 3H2SO4 ! Al2(SO4)3 + 3H2
Oxidants and Reducing Agents
-2
+1
+1 -1
+1 -1
+1
-2
AgNO3 + NaCl ! AgCl(s) + NaNO3
+5
+5
NOT a redox reaction
0
+1
-2
+3
-2
0
2Al + 3H2SO4 ! Al2(SO4)3 + 3H2
+6
+6
Oxidants and Reducing Agents
-2
+1
+1 -1
+1 -1
+1
-2
AgNO3 + NaCl ! AgCl(s) + NaNO3
+5
+5
NOT a redox reaction
0
+1
-2
+3
-2
0
2Al + 3H2SO4 ! Al2(SO4)3 + 3H2
+6
+6
a redox reaction
Balancing Redox Reactions
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
Balancing Redox Reactions
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
Step 1. Assign oxidation numbers
Balancing Redox Reactions
+1
+1
+1
+1
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
Step 1. Assign oxidation numbers
Balancing Redox Reactions
+1
-2
+1
+1
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
Step 1. Assign oxidation numbers
Balancing Redox Reactions
+1
-2
+1
+1
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
-1
-1
Step 1. Assign oxidation numbers
-1
0
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Step 3. Determine the number of electrons: (a) gained by
the oxidant
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Step 3. Determine the number of electrons: (a) gained by
the oxidant (3)
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Step 3. Determine the number of electrons: (a) gained by
the oxidant (3), and (b) lost by the reducing agent
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Step 3. Determine the number of electrons: (a) gained by
the oxidant (3), and (b) lost by the reducing agent (1)
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Step 3. Determine the number of electrons: (a) gained by
the oxidant (3), and (b) lost by the reducing agent (1)
Step 4. (the key step) Assign coefficients to match the
number of electrons lost and gained.
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Step 3. Determine the number of electrons: (a) gained by
the oxidant (3), and (b) lost by the reducing agent (1)
Step 4. (the key step) Assign coefficients to match the
number of electrons lost and gained.
K2Cr2O7 + 6HI ! KI + CrI3 + 3I2 + H2O
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Step 3. Determine the number of electrons: (a) gained by
the oxidant (3), and (b) lost by the reducing agent (1)
Step 4. (the key step) Assign coefficients to match the
number of electrons lost and gained.
Step 5. Complete balancing by inspection (by guessing)
K2Cr2O7 + 6HI ! KI + CrI3 + 3I2 + H2O
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Step 3. Determine the number of electrons: (a) gained by
the oxidant (3), and (b) lost by the reducing agent (1)
Step 4. (the key step) Assign coefficients to match the
number of electrons lost and gained.
Step 5. Complete balancing by inspection (by guessing)
K2Cr2O7 + 6HI ! 2KI + 2CrI3 + 3I2 + 7H2O
Balancing Redox Reactions
+1
-2
+1
+1
+3
+1 -2
K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O
+6
-1
-1
-1
0
Step 1. Assign oxidation numbers
Step 2. Find and the oxidant and reducing agent
Step 3. Determine the number of electrons: (a) gained by
the oxidant (3), and (b) lost by the reducing agent (1)
Step 4. (the key step) Assign coefficients to match the
number of electrons lost and gained.
Step 5. Complete balancing by inspection (by guessing)
K2Cr2O7 + 14HI ! 2KI + 2CrI3 + 3I2 + 7H2O
READ SECTION 4.6:
The activity series of the metals
READ (!) SECTION 4.6:
The activity series of the metals
Reversible Reactions
CaCO3 ! CaO + CO2
CaO + CO2 ! CaCO3
CaCO3
CaO + CO2
equilibrium system
Practice Problem
(4.70) Identify the oxidizing agent and the reducing agent in
each of the following:
8H+ + 6Cl¯ + Sn + 4NO3¯ ! SnCl62¯ + 2NO2 + 4H2O
Practice Problem
(4.70) Identify the oxidizing agent and the reducing agent in
each of the following:
8H+ + 6Cl¯ + Sn + 4NO3¯ ! SnCl62¯ + 2NO2 + 4H2O
2MnO4¯ + 10Cl¯ + 16H+ ! 5Cl2 + 2Mn2+ + 8H2O
Practice Problem
(4.75) Use the oxidation number method to balance the
following equations by placing coefficients. Identifiy the
reducing and oxidizing agents:
(b) I2 + Na2S2O3 ! Na2S4O6 + NaI
Practice Problem
(4.83) Balance the following redox reaction and classify it as
a combination, decomposition, or displacement reaction:
(a) Ca + H2O ! Ca(OH)2 + H2
(b) NaNO3 ! NaNO2 + O2
(c) C2H2 + H2 ! C2H6