Objectives◦Define Brønsted-Lowry acids and bases.◦Differentiate between Brønsted-Lowry and Arrhenius acids and bases.◦Identify conjugate acid-base pairs.◦Identify the proton transfer in Brønsted-Lowry acid-base reactions.
Chapter 15.1Acids and Bases
Arrhenius Acids and Bases
Arrhenius acid: any substance that
produces H3O+ when dissolved in water.
Arrhenius base: any substance that
produces OH- when dissolved in water.
Arrhenius acids and bases are limited to
aqueous solutions.
Brönsted-Lowry Acids and Bases
Brönsted-Lowry acid: proton (H+) donor
Brönsted-Lowry base: proton (H+)
acceptor
Brönsted-Lowry acid-base reactions
involve the transfer of a proton (H+) from
an acid to a base.
Brönsted-Lowry acids and bases are not
limited to aqueous solutions.
Conjugate Acid-Base Pairs
Conjugate acid-base pairs: molecules or
ions that differ by a single proton (H+).
The acid contains the proton (H+) that is
transferred to a molecule or ion.
The conjugate base is the molecule or ion
remaining after the loss of the proton (H+).
Conjugate Acid-Base Pairs
HF(aq) + H2O(l) ⇌ F-(aq) + H3O+(aq)
H+ is transferred from HF to H2O
acid conjugate base
base conjugate acid
Conjugate Acid-Base Pairs
Acid Base
HF F-
H2SO4 HSO4-
HSO4- SO4
2-
NH4+ NH3
H3O+ H2O
H2O OH-
H2O and HSO4- are amphoteric, acting as
both an acid and a base.
Brönsted-Lowry Acid-Base Reactions
acid + base ⇌ conj. base + conj. acid
HF + NH3 ⇌ F- + NH4+
HNO2 + H2O ⇌ NO2- + H3O
+
H2O + NH2- ⇌ OH- + NH3
In Class Example
Identify the acid-base conjugate pairs.
HCN(aq) + H2O(l) ⇌ H3O+(aq) + CN- (aq)
CH3NH2(aq) + H2O(l) ⇌ CH3NH3+(aq) + OH-(aq)
Objectives◦Relate hydrogen ion concentration to hydroxide ion concentration in aqueous solutions.◦Define pH and use it to express concentrations.◦Convert between concentrations of hydrogen ion and hydroxide ion, pH, and pOH. September 15th, 2016
Chapter 15.2Autoinoization of Water
Autoionization of Water
H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)
H2O and H3O+ are a base-conjugate acid
pair.
H2O and OH- are an acid-conjugate base
pair.
Autoionization of Water
H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)
Kw = [H3O+][OH-]
Kw is temperature dependent and is equal
to 1.0 x 10-14 at 25 oC.
Autoionization of Water
H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)
In pure water, [H3O+] = [OH-]
Kw = [H3O+][OH-] = 1.0 x 10-14
[H3O+] = [OH-] = 1.0 x 10-7M
Calculating [H3O+] and [OH-] in non-pure water
Kw = 1.0x10-14 = [H3O+][OH-]
Adding an acid or a base to water changes
the concentration of both H3O+ and OH-
simultaneously.
Calculate the [OH-] in a solution with a
[H3O+] of 3.6 10-3 M.
pH Scale
pH stands for the negative log of the
hydronium ion concentration, -log10[H3O+]
• Calculate the pH of a solution that has a
0.0034 M [H3O+].
pH = -log(0.0034) = 2.47
pH units are always given to TWO decimal places.
pH and pOH Realtionship
[H3O+][OH-] = Kw = 1.0 10-14
pH + pOH = pKw = 14.0014
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
pH pOH
Acidic
Basic
Acidic Neutral Basic
pH <7 = 7 >7
pOH >7 = 7 <7
Objectives◦Define strong acids and bases.◦List the species that are strong acids and bases.◦Calculate the concentrations of species, the pH, and the pOH of solutions of strong acids and bases.
September 15th, 2016
Chapter 15.3Strong Acids and Bases
Strong Acids
HA(aq) + H2O (l) 100%
H3O+(aq) + A-(aq)
Strong acids ionize completely (100%) in
solution.
Strong Acids
There are six strong acids:
HCl hydrochloric acid
HBr hydrobromic acid
HI hydroiodic acid
HNO3 nitric acid
HClO4 perchloric acid
H2SO4 sulfuric acid
Strong Bases
Strong bases quantitatively produce
hydroxide ions in water.
Common strong bases include the group
IA and soluble IIA oxides and hydroxides.
NaOH(s) Na+(aq) + OH-(aq)
Li2O(s) + H2O(l) 2Li+(aq) + 2OH-(aq)