Chapter 4: Types of Chemical
Reactions
Goals:
• To be able to predict chemical reactivity.
• To know how to synthesize specific
compounds.
Types of Reactions
•
•
•
•
•
Acid-Base: proton-transfer
Oxidation-Reduction: electron-transfer
Precipitation: formation of insoluble salts
Gas Forming
Organic:
– Substitution
– Addition
– Elimination
Reactions in Aqueous Solution
Unless mentioned, all reactions studied this
and next week occur in aqueous solution.
Electrolytes
Strong Electrolytes: solute breaks apart to give ions in solution.
NaCl  Na+ + Cl-
Weak Electrolytes: solute partially breaks apart to give ions.
CH3CO2H  CH3CO2- + H+
Nonelectrolytes: no ions formed.
CH3CH2OH
happens less than 5%
Brønsted-Lowery Acid-Base
Definitions
• An acid is a substance that donates a proton (H+)
to a base
• A base is a substance that accepts a proton (H+)
from an acid
Brønsted-Lowery Definitions
• acid: donates a proton (H+) to a base
• base: accepts a proton (H+) from an acid
• Acid-base reactions can be reversible:
reactants  products or
products  reactants
Brønsted-Lowery Definitions
• An acid is a substance that donates a proton (H+)
to a base
• A base is a substance that accepts a proton (H+)
from an acid
• Acid-base reactions can be reversible:
reactants  products or
products  reactants
Important Acids and Bases
Strong Acids:
Strong Bases:
HCl
hydrochloric
HBr
hydrobromic
HI
hydroiodic
HNO3
nitric
H2SO4
sulfuric
HClO4
perchloric
Weak Acid:
CH3CO2H
LiOH
lithium hydroxide
NaOH
sodium hydroxide
KOH
Ca(OH)2
calcium hydroxide
Ba(OH)2
barium hydroxide
Weak Base:
NH3
acetic
Any other acids are WEAK
potassium hydroxide
ammonia
STRONG acids in water: 100% of acid molecules form
ions:
HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)
H3O+ is
hydronium ion
WEAK acids in water, ~5% or less of acid molecules
form ions (acetic, H3PO4, H2CO3)
Polyprotic Acids
multiple acidic H atoms
H2SO4  H+ + HSO4HSO4-  H+ + SO42-
Not all H’s are acidic:
CH3CO2H
If H3PO4 reacts as an acid, which
of the following can it not make?
•
•
•
•
1. H4PO4+
2. H2PO43. HPO424. PO43-
2-
If C2O4 reacts in an acid-base
reaction, which of the following
can it not make?
• 1. H2C2O4
• 2. HC2O4• 3. 2 CO2
Acid-Base Reactions
Strong Acid + Strong Base
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
acid
base
“salt”
water
Acid-Base Reactions
Diprotic Acids or Bases
H2SO4(aq) + NaOH(aq) 
H2SO4(aq) + Ba(OH)2(aq) 
HCl(aq) + Ba(OH)2(aq) 
Acid-Base Reactions
Strong Acid + Weak Base
HCl(aq) + NH3(aq)  NH4Cl(aq)
Acid-Base Reactions
Weak Acid + Strong Base
HCN(aq) + NaOH(aq)  NaCN(aq) + H2O(l)
acid
base
“salt”
water
Net Ionic Equations
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
What really happens:
H+(aq) + OH-(aq)  H2O(l)
Sodium ion and chloride ion are “spectator ions”
Reactions involving weak bases
HCl(aq) + NH3(aq)  NH4+(aq) + Cl-(aq)
Net-Ionic Equation:
NH3(aq) + H+(aq)  NH4+(aq)
CH3CO2H(aq) + NaOH(aq) 
• 1. CH3CO2H2+(aq) + NaO(aq)
• 2. CH3CO2-(aq) + H2O(l) + Na+(aq)
• 3. CH4(g) + CO2(g) + H2O(l)
HCN(aq) + NH3(aq) 
• 1. NH4+(aq) + CN-(aq)
• 2. H2CN+(aq) + NH2-(aq)
• 3. C2N2(s) + 3 H2(g)
Solution Concentration: Molarity
• Molarity = moles solute per liter of solution
• 0.30 mol NH3 dissolved in 0.500 L
Concentration =
• Written like: [NH3] = 0.60 M
pH Scale
• In pure water, a few molecules
ionize to form H3O+ and OH–
H2O + H2O  OH– + H3O+
• In acidic and basic solutions,
these concentrations are not
equal
acidic: [H3O+] > [OH–]
basic: [OH–] > [H3O+]
neutral: [H3O+] = [OH–]
pH Scale
• Measure how much H3O+ is in a
solution using pH
• pH < 7.0 = acidic
• pH > 7.0 = basic
• pH = 7.0 = neutral
• Measure of H3O+ and OH–
concentration (moles per liter) in a
solution
• As acidity increases, pH decreases
pH Scale
• The pH scale is logarithmic:
100
10
1
0.1
0.01
• pH
102
101
100
10–1
10–2
log(102) = 2
log(101) = 1
log(100) = 0
log(10–1) = –1
log(10–2) = –2
= –log [H3O+]
• pH if [H3O+] = 10–5? 10–9?
Acidic or basic?
• pH if [H3O+] = 0.000057 M?
+
O]
Finding [H3
[H3O+] = 10-pH
What is [H3O+] if pH = 8.9?
from pH
pH: Quantitative Measure of
Acidity
• Acidity is related to concentration of H+
(or H3O+)
• pH = -log[H3O+]