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 15.1 Acids and Bases
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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.
Student Example
Calculate the pH of an aqueous solution
that has [OH-] = 7.7x10-7
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
In Class Example
What is the pH of a 0.050 M HCl solution?
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)
Student Example
Calculate the pH of a 0.035 M barium
hydroxide, Ba(OH)2, solution.
Student Example
Calculate the concentration of a HCl
solution having a pH of 3.75.
Calculate the concentration of a KOH
solution having a pH of 11.60.
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