Chemistry 100
Chapter 14
Acids and Bases
Acids and Bases
Acids: sour
Bases: bitter or salty
Acids and Bases
Arrhenius definition:
(If H2O is involved.)
Acid: produces H3O+
CH3COOH(aq) + H2O(l)
CH3COO-(aq) + H3O+(aq)
H3O+ (Hydronium ion): H+(aq) + H2O(l)
H3O+(aq)
Base: produces OHNaOH(s)
H2O
NH3(aq) + H2O(l)
Na+(aq) + OH-(aq)
NH4+(aq) + OH-(aq)
Acids and Bases
Bronsted and Lowry definition:
(If H2O is not involved.)
Acid: donates H+ (proton)
Base: accepts H+ (proton)
HCl
acid
+
Cl-
H 2O
base
+
H3 O +
Conjugate Conjugate
base
acid
Conjugate acid-base pair
Conjugate acid-base pair
Acids and Bases
HCl
+
H 2O
+
H3 O +
Proton (H+) is transferred.
: :
+
H O H + :Cl: H
:
: :
:
H O: + H Cl :
H
Cl-
Acids and Bases
CH3COOH + NH3
acid
base
CH3COO- + NH4+
Conjugate
base
Conjugate
acid
Conjugate acid-base pair
Conjugate acid-base pair
C6H5OH + H2O
acid
base
C 6 H 5 O- +
Conjugate
base
H 3 O+
Conjugate
acid
Conjugate acid-base pair
Conjugate acid-base pair
Acids and Bases
Weak acid and base: is partially ionized in aqueous solution.
produces less H+ and OH-
CH3COOH(aq) + H2O(l)
NH3(aq) + H2O(l)
CH3COO-(aq) + H3O+(aq)
NH4+(aq) + OH-(aq)
Strong acid and base: is completely ionized in aqueous solution.
produces more H+ and OH-
HCl(aq) + H2O(l)
NaOH(aq) + H2O(l)
Cl-(aq) + H3O+(aq)
Na+(aq) + OH-(aq)
Electrolytes
bulb
Electrolyte: conducts an electric current.
Na+
Clelectrolyte
+
-
Ionization (Dissociation)
NaCl → Na+ + Cl-
strong electrolytes: molecules dissociate completely into ions (NaCl).
weak electrolytes: molecules dissociate partially into ions (CH3COOH).
nonelectrolytes: molecules do not dissociate into ions (DI water).
Acids and Bases
Strong acid/base  Strong electrolyte
Weak acid/base  Weak electrolyte
HCl(aq) + H2O(l)
Cl-(aq) + H3O+(aq)
Acids and Bases
Acid
Strong HI
Acid s HCl
H2 SO4
HNO3
H3 O+
HSO4
H3 PO4
CH3 COOH
H2 CO3
H2 S
H2 PO4 NH4 +
HCN
C6 H5 OH
HCO3 2HPO4
Weak H2 O
A cids C2 H5 OH
N ame of acid
Hydroiodic acid
Hydrochloric acid
Su lfu ric acid
N itric acid
Hydron iu m ion
Hydrogen su lfate ion
Ph os phoric acid
Acetic acid
Carb on ic acid
Hydrogen su lfid e
D ihydrogen p hosph ate
Ammon ium ion
Hydrocyanic acid
Ph enol
Conjugate
Base
I
Cl
HSO4
NO3
H2 O
2SO4
H2 PO4
CH3 COO
HCO3
HS
HPO4 2 NH3
CNC6 H5 O-
CO3 2 Bicarbonate ion
3Hydrogen ph os phate ion PO4
OH
Water
C2 H5 O
Eth anol
N ame of ion
Iod ide
Weak
Chloride
Bases
Hydrogen su lfate
N itrate
Water
Su lfate
D ihydrogen p hosph ate
Acetate
Bicarbonate
Hydrogen su lfid e
Hydrogen ph os phate
Ammon ia
Cyan ide
Ph enoxide
Carb on ate
Ph os phate
Hydroxide
Eth oxide
A strong acid contains a weak conjugate base.
S trong
Bas es
Acids and Bases
Monoprotic acids
Diprotic acids
Triprotic acids
HCl
H2SO4
H3PO4
Amphiprotic: it can act as either an acid or a base.
HCl(aq) + H2O(l)
Cl-(aq) + H3O+(aq)
base
NaOH(aq) + H2O(l)
acid
Na+(aq) + OH-(aq)
Acids and Bases
Oxyacids: acidic H is attached to an oxygen atom.
H2SO4
H3PO4
HNO3
Organic acids: contain carboxyl group (-COOH).
They are usually weak.
CH3COOH
Naming binary acids
Hydro
+
Anion : -ide ion
-ic acid
HF
F-: flouride ion
Hydroflouric acid
HCl
Cl-: chloride ion
Hydrochloric acid
H2S
S2-: sulfuride ion
Hydrosulfuric acid
Naming ternary acids
Anion:
-ite ion
-ous acid
-ate ion
-ic acid
HNO2
NO2-: Nitrite ion
Nitrous acid
HNO3
NO3-: Nitrate ion
Nitric acid
H2CO3
CO32-: carbonate ion
carbonic acid
H2SO3
SO32-: sulfurite ion
sulfurous acid
Ionization constant
HA + H2O
Equilibrium constant
Acid ionization constant
K=
A- + H3O+
[A-] [H3O+]
not for strong acids
[HA] [H2O]
Ka = K [H2O] =
[A-] [H3O+]
[HA]
- Log Ka = pKa
Ka ↑ or pKa ↓
Stronger acid
Ka < 1
Ionization of water
H2O + H2O
OH- + H3O+
KW = [H3O+] [OH-] = (1×10-7) (1×10-7)
[H3O+] [OH-] = 1×10-14
pH + pOH = 14
[H+] and [OH-]
[H+] = [OH-]
Neutral solution
[H+] > [OH-]
Acidic solution
[H+] < [OH-]
Basic solution
pH and pOH
pH = - log [H3O+] or -log [H+]
pOH = - log [OH-]
pH scale:
0
7
14
Acid
Neutral
Base
[H3O+] ↑
[H3O+] ↓ and [OH-] ↑
pH meter and pH indicators
Nature & pH indicators
Bigleaf Hydrangea
In basic soil (alkaline)
In acidic soil
pH of strong acids
HCl(aq) + H2O(l)
Cl-(aq) + H3O+(aq)
0.10 M HCl  pH = ?
0.10 M HCl  0.10 M H+ and 0.10 M Cl-
[H+] = 0.10 M
pH = -log [H+]
pH = -log (0.10) = 1.00
Acid Reactions
1. Reaction with metals (strong acids): a salt and H2 are produced.
Mg(s) + 2HCl(aq)
MgCl2(aq) + H2(g)
2. Reaction with metal hydroxides: a salt and water are produced.
KOH(aq) + 2HCl(aq)
KCl(aq) + H2O(l)
Acid Reactions
3. Neutralization: reaction between an acid and a base.
A salt and water are produced.
KOH(aq) + 2HCl(aq)
KCl(aq) + H2O(l)
2NaOH(aq) + H2SO4(aq)
Na2SO4(aq) + 2H2O(l)
Strong acid reacts with strong base
to produce the weaker acid and weaker base.
(This is the direction of a reaction)
Titration (Neutralization reaction)
B
MB: known
MA: unknown
VB: known
VA: known
Equivalence point:
A
Equal amount of acid (H+) and base (OH-) (pH = 7).
H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l)
Acid
Base
Titration (Neutralization reaction)
Practice:
H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l)
How much 0.430 M NaOH solution in liters do we need to completely neutralize
0.205 L of 0.150 M H2SO4 solution?
0.205 L H2SO4 solution ×
0.150 mol H2SO4
1L H2SO4 solution
×
2 mol NaOH
1 mol H2SO4
×
1 L Solution NaOH
=
0.430 mol NaOH
0.143L NaOH solution
Buffers
Acid or Base
pH stays constant.
Buffer
A buffer resists changes in pH when limited
amounts of acid or base are added.
Buffers
Our blood is a buffer solution.
Acid
pH of blood ≈ 7.4
Acid
Base
Shock
Absorber
Buffer Composition
Weak Acid + its Conjugate base (in equilibrium)
salt of the weak acid
CH3COOH + CH3COO-Na+
CH3COOH / CH3COO-
Buffers
pH of blood = between 7.35 and 7.45
Carbonate buffer
H2CO3 / HCO3-
Phosphate buffer
H2PO4- / HPO42-
Proteins buffer
How do buffers work?
Carbonate buffer
If we eat an acidic food:
If we eat a basic food:
H2CO3 / HCO3-
HCO3- + H3O+ → H2CO3 + H2O
H2CO3 + OH- → HCO3- + H2O
pH of Buffers
HA(aq)
Weak acid
A-(aq) + H+(aq)
Conjugate base
[A-]
pH = pKa + log
[HA]
Henderson-Hasselbalch equation
[HA]: concentration of the weak acid
[A-]: concentration of its conjugate base
pKa of the weak acid