Chapter 16:
Equilibrium in AcidBase Systems
16.2a: Bronsted-Lowry Acid-Base
Concept
Definition of Acid and Base

Bronsted-Lowry
independently created by two scientists around the
same time (1923)
 looked at how acid/base acted in reactions instead
of their properties in aqueous solutions
 theoretical definitions based upon proton transfer
during a reaction

Proton transfer concept
Acid: molecule or ion that is a proton (H+) donor
 HCl + H2O  H3O+ + Cl
Base: molecule or ion that is a proton (H+)
acceptor
 NH3 + H2O  NH4+ + OH
Bronsted-Lowry concept



B-L acid a proton donor; B-L base a proton
acceptor
B-L neutralization is a competition for
protons from the SA to the SB
B-L rxtn. eqtn. is an eqtn. that shows this
transfer of protons from one entity to
another
Acids or Bases?

C5H5N






acid (weak)
base (weak)
HC2H3O2


base (strong)
CH3NH2


acid (strong)
KOH

base (weak)
H2CO3


acid (weak)
NH3
H2SO4

base (strong)
HF


base (weak)
Mg(OH)2


acid (weak)
HI

acid (strong)
Acid – Base Reactions

Identify the acids and bases of the
following reactions
C6H5NH2 + H2O  C6H5NH3+ + OHB
A
 HNO3 + H2O  H3O+ + NO3A
B
 HCH3COO + H2O  H3O+ + CH3COOA
B

Acid-Base Reactions

Amphoteric Substances
proper term used in B-L reactions
 a substance that can react as either acid or
base depending on what they are mixed with
 example: water, HSO4

Amphiprotic
incorrect term to use with B-L rxtns.
 refers to an entity (ion or molecule)

Amphoteric Water
Water as a base (proton acceptor)
Water as an acid (proton donor)
Conjugate Acid-Base Pairs
Conjugate acids and bases are always created
by a B-L reaction (as products)

Conjugate base
 an acid that has lost a H+
 missing a hydrogen
 ex: H2PO4-, OH-, Cl-

Conjugate acid
 a base that has gained a H+
 has an extra hydrogen
 NH4+, C6H5NH3+, H3O+
A pair of substances with formulas that differ only by
a proton is called a conjugate acid-base pair
Identify the parts of these
reactions




C6H5NH2 + H2O  C6H5NH3+ + OHbase
acid
CA
CB
HNO3 + H2O  H3O+ + NO3acid
base CA
CB
HCH3COO + H2O  H3O+ + CH3COOacid
base CA
CB
NH3 + H2O  NH4+ + OHbase acid
CA
CB
Homework



Textbook p724 #1-6
Textbook p726 #7
LSM 16.2A summary 1