Download Session 11 - Columbia University

Acids, Bases, and Salts
Preparation for College Chemistry
Columbia University
Department of Chemistry
Chapter Outline
Acids and Bases Definitions
The p- function. pH, pKa
Neutralization reactions and salts
Titration curves
Acid Rain
Acids and Bases Definitions
Theory
Arrhenius
1884
Brönsted-Lowry
1923
Lewis
1930’s
Acid
Base
H-containing, releases
H + in water
OH-containing,
releases OH - in water
Proton (H +) donor
Proton (H +) acceptor
Electron-pair acceptor
Electron-pair donor
Acid-Base Conjugate Pair
acid1 (aq)
base1(aq) + H +(aq)
base2(aq) + H +(aq)
acid1 (aq) + base2(aq)
HC2H3O2 (aq) + H2O
acid2
base1 aq) + acid2 aq)
H3O+(aq) + C2H3O2 -(aq)
Acidity Constant, Ka
HC2H3O2 (aq) + H2O
weak base
weak acid
Keq =
strong acid
strong acid
strong base
[H3O +] [C2H3O2 -]
[H2O] [HC2H3O2]
Keq [H2O] = Ka =
HCl (aq) + H2O
H3O+(aq) + C2H3O2 -(aq)
[H3O +] [C2H3O2 -]
[HC2H3O2]
H3O+(aq) + Cl -(aq)
weak base
Basicity Constant, Kb
NH4+(aq) + OH -(aq)
NH4OH (aq) + H2O
weak base
weak acid
Keq =
strong acid
strong base
[NH4 +] [OH -]
[H2O] [NH4OH]
Keq [H2O] = Kb =
[NH4 +] [OH -]
[NH4OH]
NaOH (aq) + H2O
Na +(aq) + OH -(aq)
strong base
weak acid
Ka and Kb values
Ka
1.8x 10 -4
HCNO
2.0x 10 -4
HF
6.5x 10 -4
HNO2
4.5x 10 -4
HC2H3O2
HC6H5O2
HCN
Strength
HCHO2
Base
Mg(OH)2
NH3
N2H2
Al(OH)3
1.3x 10 -10
NH2OH
PH3
1.0x 10 -1
5.6x 10 -4
Be(OH)2
1.8x 10 -5
4.0x 10 -10
Kb
5.6x 10 -5
1.1x 10 -6
Strength
Acid
1.9x 10 -8
1.x 10 -8
1.x 10 -28
p-function = -log fx
H2O + H2O
H3O+(aq) + OH -(aq)
Kw = [H3O +] [OH -] = 1x 10 -14
logKw = log [H3O +] + log[OH -] = - 14
x -1
-logKw = -log[H3O +] - log[OH -] = 14
pKw = p[H3O +] + p[OH -] = 14
pH + pOH = 14
pH Scale
[H+] (mol/L)
pH
[H+] (mol/L)
pH
7
13
1x 10 -6
6
12
1x 10 -5
5
1x 10 -11
11
1x 10 -4
4
1x 10 -10
10
1x 10 -3
1x 10 -9
9
1x 10 -2
1x 10 -8
8
1x 10 -1
1x 10 -13
1x 10 -12
Acidity
1x 10 -7 Neutral
Basicity
14
1x 10 -14
3
2
1
Hydrolysis
salt (aq) + H2O (l)
base (aq) + acid (aq)
Base
Acid
Salt pH
Strong
Strong
Neutral
Strong
Weak
Basic
Weak
Strong
Acidic
Weak
Weak
Depends on Ka and Kb
Neutralization Reactions
NaOH (aq) + HCl (aq)
NaCl (aq) + H2O (l)
Writing the ionic equation and eliminating SPECTATOR IONS:
Na+(aq) + OH-(aq) + H+ + Cl-(aq)
Na+(aq) + Cl-(aq) + H2O (l)
Net ionic equation:
OH-(aq) + H+
HC2H3O2 (aq) + NaOH (aq)
H2O (l)
Na C2H3O2 (aq) + H2O(l)
Net ionic equation:
HC2H3O2 (aq) + OH-(aq)
C2H3O2-(aq) + H2O (l)
Buffer Solutions
Resist changes in pH when small amounts of diluted acids and
bases are added.
Weak acid mixed with its conjugate base
Two types:
Weak base mixed with its conjugate acid
HC2H3O2 (aq) + H2O
NaC2H3O2 (aq)
H3O+(aq) + C2H3O2 -(aq)
Na+(aq) + C2H3O2 -(aq)
Henderson-Hasselbalch Equation
H3O+(aq) + A -(aq)
HA (aq) + H2O
Ka =
[H3O +] [A -]
[HA]
Applying p function:
-logKa= - log[H3O
+]
- log
or
pH =
pKa + log
AHA
AHA
Replaceable Hydrogens
Monoprotic Acids: HCl, HC2H3O2 , HNO3 , HC9H19O2
Diprotic Acids:
H2SO4 , H2C2O2 , H2C2O2
Polyprotic Acids: H3PO4
The Carboxylic Functional Group
C
OH
O
Titration curves
Strong Acid - Strong Base
Strong Base - Strong Acid
Strong Acid - Weak Base
Strong Base - Weak Acid