Chemistry 102(01) Fall 2010
Instructor: Dr. Upali Siriwardane
e-mail: upali@latech.edu
Office: CTH 311 Phone 257-4941
Office Hours: M,W 8:00-9:00 & 11:00-12:00 am;
Tu,Th,F 8:00 - 10:00 am.
Test Dates: September 23, October 21, and November 16;
Comprehensive Final Exam: November 18, 2010
Exam: 10:0-10:15 am, CTH 328.
September 23, 2010 (Test 1): Chapter 13
October 21, 2010 (Test 2): Chapters 14 & 15
November 16, 2010 (Test 3): Chapters 16, 17 & 18
Comprehensive Final Exam: November 18, 2010 :Chapters 13,
14, 15, 16, 17 and 18
CHEM 102, Fall 2010, LA TECH
16-1
Chapter 16. Acids and Bases
16.1
16.2
16.3
16.4
16.5
16.6
16.7
16.8
16.9
16.10
The Brønsted-Lowry Concept of Acids and Bases
Types of acids/bases:Organic Acids and Amines
The Autoionization of Water
The pH Scale
Ionization Constants of Acids and Bases
Problem Solving Using Ka and Kb
Molecular Structure and Acid Strength
Acid-Base Reactions of Salts
Practical Acid-Base Chemistry
Lewis Acid and Bases
CHEM 102, Fall 2010, LA TECH
16-2
Types of Reactions
a) Precipitation Reactions.
Reactions of ionic compounds or
salts
b) Acid/base Reactions.
Reactions of acids and bases
c) Redox Reactions.
reactions of oxidizing & reducing
agents
CHEM 102, Fall 2010, LA TECH
16-3
What are Acids &Bases?
Definition?
a) Arrhenius
b) Bronsted-Lowry
c) Lewis
CHEM 102, Fall 2010, LA TECH
16-4
Arrhenius Definitions
Arrhenius, Svante August (1859-1927), Swedish chemist,
1903 Nobel Prize in chemistry
• Acid
•
•
Anything that produces hydrogen ions in a water
solution.
HCl (aq)
Base
solution.
+
H ( aq) + Cl ( aq)
Anything that producs hydroxide ions in a water
+
NaOH (aq)
Na ( aq) + OH ( aq)
Arrhenius definitions are limited proton acids and
hydroxide bases to aqueous solutions.
CHEM 102, Fall 2010, LA TECH
16-5
Brønsted-Lowry definitions
Expands the Arrhenius definitions to include many bases
other than hydroxides and gas phase reactions
Acid
Proton donor
Base
Proton acceptor
This definition explains how substances like ammonia can
act as bases.
Eg. HCl(g) + NH3(g) ------> NH4Cl(s)
HCl (acid), NH3 (base).
NH3(g) + H2O(l)
CHEM 102, Fall 2010, LA TECH
NH4+ + OH16-6
Lewis Definition
G.N. Lewis was successful in including acid and bases
without proton or hydroxyl ions.
Lewis Acid: A substance that accepts an electron pair.
Lewis base: A substance that donates an electron pair.
E.g.
BF3(g) + :NH3(g)
F3B:NH3(s)
the base donates a pair of electrons to the acid forming a
coordinate covalent bond common to coordination
compounds. Lewis acids/bases will be discussed later in
detail
CHEM 102, Fall 2010, LA TECH
16-7
Dissociation
Strong Acids:
HCl(aq) + H2O(l)
H3+O(aq) + Cl-(aq)
H2SO4(aq) + H2O(l)
H3+O(aq) + HSO4-(aq)
Dissociation Equilibrium Weak Acid/base:
H2O(l) + H2O(l)
H3+O(aq) + OH-(aq)
This dissociation is called autoionization of water.
HC2H3O2(aq) + H2O(l)
H3+O(aq) + C2H3O2-(aq)
NH3 (aq) + H2O(l)
NH4+ + OH-(aq)
Equilibrium constants: Ka, Kb and Kw
CHEM 102, Fall 2010, LA TECH
16-8
Brønsted-Lowry Definitions
Conjugate acid-base pairs.
Acids and bases that are related by loss or gain of H+
as H3O+ and H2O.
Examples.
Acid
Base
CHEM 102, Fall 2010, LA TECH
H3O +
H2O
HC2H3O2
C2H3O2-
NH4 +
NH3
H2SO4
HSO4-
HSO4-
SO42-
16-9
Bronsted acid/conjugate base and
base/conjugate acid pairs in
acid/base equilibria
HCl(aq) + H2O(l)
H3+O(aq) + Cl-(aq)
HCl(aq): acid
H2O(l):
base
H3+O(aq):
conjugate acid
Cl-(aq):
conjugate base
H2O/ H3+O:
base/conjugate acid pair
HCl/Cl-:
acid/conjugate base pair
CHEM 102, Fall 2010, LA TECH
16-10
Select acid, base,
acid/conjugate base pair,
base/conjugate acid pair
H2SO4(aq) + H2O(l)
H 3+O(aq) + HSO4-(aq)
acid
base
conjugate acid
conjugate base
base/conjugate acid pair
acid/conjugate base pair
CHEM 102, Fall 2010, LA TECH
16-11
Types of Acids and Bases
Binary acids: HCl, HBr, HI, H2S
More than two elements: HCN
Oxyacid: HNO3, H2SO4, H3PO4
Polyprotic acids: H2SO4, H3PO4
Organic acids: R-COOH, R= CH3-, CH3CH2Acidic oxides: SO3, NO2, CO2,
Basic oxides: Na2O, CaO
Amine: NH3. R-NH2, R= CH3-, CH3CH2- : primary
R2-NH : secondary, R3-N: tertiary
Lewis acids & bases: BF3 and NH3
CHEM 102, Fall 2010, LA TECH
16-12
Strong Acid vs. Weak Acids
Strong acid
completely ionized
Hydrioidic
HI
Hydrobromic HBr
Perchloric
HClO4
Hyrdrochloric HCl
Chloric
HClO3
Sulfuric
H2SO4
Nitric
HNO3
Ka ~ 1011
Ka ~ 109
Ka ~ 107
Ka ~ 107
Ka ~ 103
Ka ~ 102
Ka ~ 20
pKa = -11
pKa = -9
pKa = -7
pKa = -7
pKa = -3
pKa = -2
pKa = -1.3
Weak acid
partially ionized
Hydrofluoric acid HF
Formic acid HCOOH
Acetic acid CH3COOH
Nitrous acid HNO2
Acetyl Salicylic acid C9H8O4
Hydrocyanic acid HCN
CHEM 102, Fall 2010, LA TECH
Ka = 6.6x10-4
Ka = 1.77x10-4
Ka = 1.76x10-5
Ka = 4.6x10-4
Ka = 3x10-4
Ka = 6.17x10-10
pKa = 3.18
pKa = 3.75
pKa = 4.75
pKa = 3.34
pKa = 3.52
pKa = 9.21
16-13
Strong Base vs. Weak Base
Strong Base
completely ionized
Lithium hydroxide
Sodium hydroxide
Potassium hydroxide
Rubidium hydroxide
Cesium hydroxide
Boarder-line Bases
Magnesium hydroxide
Calcium hydroxide
Strotium hydroxide
Barium hydroxide
Weak Base
partially ionized
Ammonia
Ethyl amine
CHEM 102, Fall 2010, LA TECH
LiOH
NaOH
KOH
RbOH
CsOH
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2
NH3
CH3CH2NH2
Kb~ 102-103
Kb~ 0.01 to0.1
Kb=1.79x10-5
Kb=5.6x10-4
pKb = 4.74
pKb = 3.25
16-14
Acid and Base Strength
• Strong acids
Ionize completely in water.
HCl, HBr, HI, HClO3,
HNO3, HClO4, H2SO4.
• Weak acids
Partially ionize in water.
Most acids are weak.
• Strong bases
• Weak bases
CHEM 102, Fall 2010, LA TECH
Ionize completely in water.
Strong bases are metal
hydroxides - NaOH, KOH
Partially ionize in water.
16-15
Common Acids and Bases
Acids
nitric
hydrochloric
sulfuric
acetic
Bases
ammonia
sodium hydroxide
*undiluted.
CHEM 102, Fall 2010, LA TECH
Formula Molarity*
HNO3
16
HCl
12
H2SO4
18
HC2H3O2
18
NH3(aq)
NaOH
15
solid
16-16
Autoionization of Water
Autoionization When water molecules react with one another to
form ions.
+
H2O(l) + H2O(l)
H3O-7(aq) + OH-7(aq)
(10 M) (10 M)
Acids and bases alter the dissociation equilibrium of water based on
Le Chaterlier’s principle
Kw
+
= [ H3O ] [ OH ]
-14
o
= 1.0 x 10
at 25 C
Note: [H2O] is constant and is included in Kw.
CHEM 102, Fall 2010, LA TECH
ion product
of water
16-17
pH and other “p” scales
Substance
pH
need to measure and use acids
1We
M HCl
0.0 and bases over a very
largejuices
concentration range. 1.0 - 3.0
Gastric
pH andjuice
pOH are systems to keep2.2
track
Lemon
- 2.4of these very large
ranges.
Classic
Coke
2.5
+
pH
= -log[H3O5.0
]
Coffee
= -log[OH ]7.0
PurepOH
Water
Blood
7.35 - 7.45
pH + pOH = 14
Milk of Magnesia
10.5
Household ammonia
12.0
1M NaOH
14.0
CHEM 102, Fall 2010, LA TECH
16-18
pH scale
A logarithmic
scale used to keep track of the large changes in
+
[H ].
0
7
-14
10
M
Very
acidic
10
-7
M 10-14 M
Neutral
14
Very
Basic
When you add an acid to, the pH gets smaller.
When you add a base to, the pH gets larger.
CHEM 102, Fall 2010, LA TECH
16-19
pH of some common materials
Substance
1 M HCl
Gastric juices
Lemon juice
Classic Coke
Coffee
Pure Water
Blood
Milk of Magnesia
Household ammonia
1M NaOH
CHEM 102, Fall 2010, LA TECH
pH
0.0
1.0 - 3.0
2.2 - 2.4
2.5
5.0
7.0
7.35 - 7.45
10.5
12.0
14.0
16-20
pH of
Aqueous
Solutions
CHEM 102, Fall 2010, LA TECH
16-21
What is pH?
Kw = [H3+O][OH-] = 1 x 10-14
[H3+O][OH-] = 10-7 x 10-7
Extreme cases:
Basic medium
[H3+O][OH-] = 10-14 x 100
Acidic medium
[H3+O][OH-] = 100 x 10-14
pH value is -log[H+]
spans only 0-14 in water.
CHEM 102, Fall 2010, LA TECH
16-22
pH, pKw and pOH
The relation of pH, Kw and pOH
Kw = [H+][OH-]
log Kw = log [H+] + log [OH-]
-log Kw= -log [H+] -log [OH-] ;
previous equation multiplied by -1
pKw = pH + pOH; pKw = 14
since Kw =1 x 10-14
14 = pH + pOH
pH = 14 - pOH
pOH = 14 - pH
CHEM 102, Fall 2010, LA TECH
16-23
pH and pOH calculations of acid
and base
solutions
a) Strong
acids/bases
dissociation is complete for strong
such as HNO3 or base NaOH
acid
[H+] is calculated from molarity (M) of the solution
b) weak acids/bases
needs Ka , Kb or percent(%)dissociation
CHEM 102, Fall 2010, LA TECH
16-24
pH of Strong Acid/bases
Substance
pH
1 M HCl
0.0
-(aq)
HNO
(aq)
+
H
O(l)
H
+O(aq)
+
NO
3
2
3
3
Gastric juices
1.0 - 3.0
Lemon juicethe moles of H+ ions
2.2 - 2.4
Therefore,
in the solution
Classic
equal Coke
to moles of HNO3 at2.5the beginning.
Coffee
5.0
+] = 0.2 mole/L
[HNO
]
=
[H
Pure
Water
7.0
3
Blood
7.35 - 7.45
pH
=
-log
[H+]
Milk of Magnesia
10.5
Household ammonia
= -log(0.2) 12.0
1M NaOH
14.0
pH
CHEM 102, Fall 2010, LA TECH
is
= 0.699
16-25
pH of 0.5 M H2SO4 Solution
H2SO4(aq) + H2O(l)
H3+O(aq) + HSO4-(aq)
HSO4-(aq) + H2O(l)
H3+O(aq) + SO42-(aq)
[H3+O][HSO4-]
H2SO4 ; Ka1 = ------------------[H2SO4]
[H3+O][SO42-]
H2SO4 ; Ka2 = ------------------- ; Ka2 ignored
[HSO4-]
CHEM 102, Fall 2010, LA TECH
16-26
pH of 0.5 M H2SO4 Solution
H2SO4(aq) + H2O(l)
+
H3 O(aq) + HSO4 (aq)
+
the moles of H ions in the solution is equal to moles of H2SO4 at the
beginning.
+
[H2SO4] = [H ] = 0.5 mole/L
+
pH = -log [H ]
pH = -log(0.5)
pH = 0.30
CHEM 102, Fall 2010, LA TECH
16-27
1.5 -2x 10-2 M NaOH.
1.5 x 10 M NaOH.
NaOH is also a strong base dissociates completely
in water.
[NaOH] = [HO- ] = 1.5 x 10-2 mole/L
pOH = -log[HO-]= -log(1.5 x 10-2)
pOH = 1.82
As defined and derived previously:
pKw= pH + pOH; pKw= 14
pH = pKw + pOH
pH = 14 - pOH
pH = 14 - 1.82 ; pH = 12.18
CHEM 102, Fall 2010, LA TECH
16-28
Mixtures of Strong and Weak
Acids
the presence of the strong acid retards the
dissociation of the weak acid
CHEM 102, Fall 2010, LA TECH
16-29
Measuring pH
Arnold Beckman
inventor of the pH
meter
father of electronic
instrumentation
CHEM 102, Fall 2010, LA TECH
16-30
Equilibrium, Constant, Ka & Kb
Ka: Acid dissociation constant for a equilibrium reaction.
Kb: Base dissociation constant for a equilibrium reaction.
Acid: HA + H2O
H3+O + ABase: BOH + H2O
[H3+O][ A-]
Ka = --------------- ;
[HA]
CHEM 102, Fall 2010, LA TECH
B+ + OH[B+ ][OH-]
Kb = ----------------[BOH]
16-31
Acid Dissociation Constant
HCl(aq) + H2O(l)
H3+O(aq) + Cl-(aq)
Ka=
[H3+O][Cl-]
----------------[HCl]
Ka=
[H+][Cl-]
----------------[HCl]
CHEM 102, Fall 2010, LA TECH
16-32
Base Dissociation Constant
NH3 + H2O
K =
CHEM 102, Fall 2010, LA TECH
NH4+ + OH-
+
[NH4 ][OH ]
[NH3]
16-33
Hydrated Metal Ions as Acids
[Fe(H2O)6]3+ (aq) + H2O ( )
[Fe(H2O)5(OH)]2+ (aq) + H3O+ (aq)
[Fe(H2 O) 5 (OH)2 ][H3 O ]
3
Ka 

6.3
10
Fe(H2 O) 3
6
CHEM 102, Fall 2010, LA TECH
16-34
Ionization
Constants
for Acids
CHEM 102, Fall 2010, LA TECH
16-35
Comparing Kw and Ka & Kb
Any compound with a Ka value greater than Kw of
water will be a an acid in water.
Any compound with a Kb value greater than Kw of
water will be a base in water.
CHEM 102, Fall 2010, LA TECH
16-36
WEAKER/STRONGER Acids and
Bases & Ka and Kb values
A larger value of Ka or Kb indicates an equilibrium
favoring product side.
Acidity and basicity increase with increasing Ka or
Kb.
pKa = - log Ka and pKb = - log Kb
Acidity and basicity decrease with increasing pKa
or pKb.
CHEM 102, Fall 2010, LA TECH
16-37
Which is weaker?
a. HNO2
b. HOCl2
c. HOCl
d. HCN
;
;
;
;
Ka= 4.0 x 10-4.
Ka= 1.2 x 10-2.
Ka= 3.5 x 10-8.
Ka= 4.9 x 10-10.
CHEM 102, Fall 2010, LA TECH
16-38
What is Ka1 and Ka2?
H2SO4(aq) + H2O(l)
H3+O(aq) + HSO4-(aq)
HSO4-(aq) + H2O(l)
H3+O(aq) + SO42-(aq)
CHEM 102, Fall 2010, LA TECH
16-39
Ka Examples
H2SO4(aq) + H2O(l)
H3+O(aq) + HSO4-(aq)
HSO4-(aq) + H2O(l)
H3+O(aq) + SO42-(aq)
[H3+O][HSO4-]
H2SO4 ; Ka1 = ------------------[H2SO4]
[H3+O][SO42-]
H2SO4 ; Ka2 = ------------------[HSO4-]
CHEM 102, Fall 2010, LA TECH
16-40
Ka Examples
HC2H3O2(aq) + H2O(l)
H3+O(aq) + C2H3O2-(aq)
[H+][C2H3O2-]
-----------------[H C2H3O2]
H C2H3O2; Ka=
NH4+ + OH-(aq)
[NH4+][OH-]
-------------[ NH3]
NH3 (aq) + H2O(l)
NH3; Kb=
CHEM 102, Fall 2010, LA TECH
16-41
How do you calculate pH of
weak acids/bases
From % dissociation
From Ka or Kb
What is % dissociation
Amount dissociated
% Dissoc. = ------------------------- x 100
Initial amount
CHEM 102, Fall 2010, LA TECH
16-42
How do you calculate % dissociation
from Ka or Kb
1.00 M solution of HCN; Ka = 4.9 x 10-10
What is the % dissociation for the acid?
CHEM 102, Fall 2010, LA TECH
16-43
1.00 M solution of HCN; Ka = 4.9 x 10-10
1.00 M solution of HCN; Ka = 4.9 x 10-10
First write the dissociation equilibrium equation:
HCN(aq) + H 2O(l) <===> H 3+O(aq) + CN-(aq)
[HCN] [H+ ] [CN- ]
Ini. Con.
1.00 M
0.0 M 0.00 M
Cha. Con
-x
x
x
Eq. Con. 1.0 - x
x
x
[H 3+O ][CN-]
x2
Ka = ----------= ---------------[HCN]
1.0 - x
CHEM 102, Fall 2010, LA TECH
16-44
1.00 M solution of HCN; Ka = 4.9 x 10-10
1.0 - x ~ 1.00 since x is small
x2
Ka = -----------; Ka = 4.9 x 10-10 = x2
1.0
x =
4.9 x 10-10 = 2.21 x 10 -5
Amount disso.
2.21 x 10 -5
----------------- x 100 =- ------------- x 100
Ini. amount
1.00
% Diss.
CHEM 102, Fall 2010, LA TECH
=2.21 x 10 -5 x 100 =
0.00221 %
16-45
% Dissociation gives x (amount
dissociated) need for pH calculation
Amount dissociated
% Dissoc. = ------------------------- x 100
Initial amount/con.
x
% Dissoc. = --------------------------- x 100
concentration
CHEM 102, Fall 2010, LA TECH
16-46
Calculate the pH of a weak acid from
% dissociation
1 M HF, 2.7% dissociated
Notice the conversion of % dissociation to a
fraction (x): 2.7/100=0.027) x=0.027
CHEM 102, Fall 2010, LA TECH
16-47
Calculate the pH of a weak acid from %
dissociation
+
-
HF(aq) + H 2O(l) <===> H 3 O(aq) + F (aq)
[H+][F-]
Ka = ----------[HF]
[HF]
[H+ ]
[F- ]
Ini. Con. 1.00 M
0.0 M
0.00 M
Chg. Con -x
x
x
Eq.Con.
1.0-0.027 0.027
0.027
pH = -log [H+]
pH = -log(0.027)
pH = 1.57
CHEM 102, Fall 2010, LA TECH
16-48
Weak acid Equilibria
Example
Determine the pH of a 0.10 M benzoic acid
solution at 25 oC if Ka = 6.28 x 10-5
HBz(aq) + H2O(l)
H3O+(aq) + Bz-(aq)
The first step is to write the equilibrium
expression
+
[H3O ][Bz ]
Ka =
[HBz]
CHEM 102, Fall 2010, LA TECH
16-49
Weak acid Equilibria
HBz
H3O+
0.00
Bz-
Initial conc., M
0.10
0.00
Change, DM
-x
x
x
Eq. Conc., M
0.10 - x
x
x
[H3O+] = [Bz-] = x
We’ll assume that [Bz-] is negligible compared to
[HBz]. The contribution of H3O+ from water is
also negligible.
CHEM 102, Fall 2010, LA TECH
16-50
Weak Acid Equilibria
Solve the equilibrium equation in terms of x
Ka = 6.28 x
x
=
10-5
=
2
x
0.10
(6.28 x 10-5 )(0.10)
H3O+ = 0.0025 M
pH = 2.60
CHEM 102, Fall 2010, LA TECH
16-51
pH from Ka or Kb
1.00 M solution of HCN; Ka = 4.9 x 10-10
First write the dissociation equilibrium
equation:
HCN(aq) + H 2O(l)
H 3+O(aq) + CN-(aq)
[HCN]
[H+ ] [CN- ]
Ini. Con.
1.00 M
0.0 M 0.00 M
Chg. Con
-x
x
x
Eq. Con. 1.0 - x
x
x
CHEM 102, Fall 2010, LA TECH
16-52
Weak Acid Equilibria
[H 3+O ][CN-]
x2
Ka = --------------=
---------------[HCN]
1.0 - x
1.0 - x ~ 1.00 since x is small
x2
Ka = -----------; Ka = 4.9 x 10-10 = x2
1.0
x = 4.9 x 10-10
= 2.21 x 10 -5
pH = -log [H+]
pH = -log(2.21 x 10-5)
pH = 4.65
CHEM 102, Fall 2010, LA TECH
16-53
The Conjugate Partners of Strong Acids
and Bases
The conjugate acid/base of a strong base/acid has
no net effect on the pH of a solution
The conjugate base of a weak acid hydrolyze in
water and basic or
pH of a solution > 7.00 E.g. Na+C2H3O2- sodium
acetate
The conjugate acid of a weak base hydrolyze in
water and acidic or
pH of a solution < 7.00 E.g NH4Cl
CHEM 102, Fall 2010, LA TECH
16-54
Hydrolysis
Reaction of a basic anion or acidic cation with water is an ordinary
Brønsted-Lowry acid-base reaction.
CH3COO (aq) + H2O(l)
CH3COOH(aq) + OH (aq)
+
+
NH4 (aq) + H2O(l)
NH3 (aq) + H3O (aq)
This type of reaction is given a special name.
Hydrolysis
The reaction
- of an anion with water to produce the conjugate acid
and OH .
The reaction
+ of a cation with water to produce the conjugate base
and H3O .
CHEM 102, Fall 2010, LA TECH
16-55
Acid-Base Properties of Typical
Ions
CHEM 102, Fall 2010, LA TECH
16-56
What salt solutions would be acidic,
basic and neutral?
1) strong acid + strong base = neutral
2) weak acid + strong base = basic
3) strong acid + weak base = acidic
4) weak acid + weak base = neutral,
basic or an acidic solution
depending on the relative strengths
of the acid and the base.
CHEM 102, Fall 2010, LA TECH
16-57
What pH? Neutral, basic or acidic?
• a)NaCl
•
neutral
• b) NaC2H3O2
•
basic
• c) NaHSO4
•
acidic
• d) NH4Cl
•
acidic
CHEM 102, Fall 2010, LA TECH
16-58
How do you calculate pH of a salt
solution?
Find out the pH, acidic or basic?
If acidic it should be a salt of weak base
If basic it should be a salt of weak acid
if acidic calculate Ka from Ka= Kw/Kb
if basic calculate Kb from Kb= Kw/Ka
Do a calculation similar to pH of a weak acid or
base
CHEM 102, Fall 2010, LA TECH
16-59
What is the pH of 0.5 M NH4Cl salt
solution?
(NH 3; Kb = 1.8 x 10-5)
Find out the pH, acidic
if acidic calculate Ka from Ka= Kw/Kb
Ka= Kw/Kb = 1 x 10-14 /1.8 x 10-5)
Ka= 5.56. X 10-10
Do a calculation similar to pH of a weak acid
CHEM 102, Fall 2010, LA TECH
16-60
Continued
NH4+ + H2O
H 3+O + NH3
[NH4+] [H3+O ] [NH3 ]
Ini. Con. 0.5 M 0.0 M
0.00 M
Change
-x
x
x
Eq. Con. 0.5 - x
x
x
[H 3+O ] [NH3 ]
Ka(NH4+) = -------------------=
[NH 4+]
x2
---------------- ;
appro.:0.5 - x . 0.5
(0.5 - x)
CHEM 102, Fall 2010, LA TECH
16-61
Continued
x2
Ka(NH4+) = ----------- = 5.56 x 10 -10
0. 5
x2 = 5.56 x 10 -10 x 0.5 = 2.78 x 10 -10
x= 2.78 x 10 -10 = 1.66 x 10-5
[H+ ] = x = 1.66 x 10-5 M
pH = -log [H+ ] = - log 1.66 x 10-5
pH = 4.77
pH of 0.5 M NH4Cl solution is 4.77
(acidic)
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Types of Acids and Bases
Binary acids
Oxyacid
Organic acids
Acidic oxides
Basic oxides
Amine
Polyprotic acids
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Influence of Molecular Structure
on Acid Strength
Binary Hydrides
• hydrogen & one other element
Bond Strengths
• weaker the bond, the stronger the acid
Stability of Anion
• higher the electronegativity, stronger the acid
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Binary Acids
Compounds containing acidic protons bonded
to a more electronegative atom.
e.g. HF, HCl, HBr, HI, H2S
The acidity of the haloacid
(HX; X = Cl, Br, I, F)
Series increase in the following order:
HF < HCl < HBr < HI
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Oxyacids
Compounds containing acidic - OH groups in the
molecule.
Acidity of H2SO4 is greater than H2SO3 because of
the extra O (oxygens)
The order of acidity of oxyacids from the a
halogen (Cl, Br, or I) shows a similar trend.
HClO4 > HClO3 > HClO2 > HClO
perchloric chloric chlorus hyphochlorus
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Influence of Molecular Structure
on Acid Strength
Oxyacids
• hydrogen, oxygen, & one other element
H-O-E
• higher the electronegativity on E, stronger the acid as
this weakens the bond between the O and H
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Oxo Acid
<
<
CHEM 102, Fall 2010, LA TECH
<
<
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Acidic Oxides
These are usually oxides of non-metallic
elements such as P, S and N.
E.g. NO2, SO2, SO3, CO2
They produce oxyacids when dissolved
in water
SO3 + H2O ---> H2SO4
CO2 + H2O ---> H2CO3
NO2 + H2O ---> HNO3
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Basic Oxides
Oxides
oxides
of
metallic
elements such as Na, K, Ca.
They produce hydroxyl bases
when dissolved in water.
e.g.
CaO + H2O ---> Ca(OH)2
Na2O + H2O ---> 2 NaOH
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Protic Acids
Monoprotic Acids: The form protic
refers to acidity due to protons.
Monoprotic acids have only one
acidic proton. e.g. HCl.
Polyprotic Acids: They have more
than one acidic proton.
e.g.
H2SO4 - diprotic acid
H3PO4 - triprotic acid.
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Polyprotic Acids
acids where more than one hydrogen per molecule
is released
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Polyprotic Acids
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Organic or Carboxylic Acids
H
H
H
H
O
C
C
C
C
H
H
H
O
nonacidic hydrogens
H
acidic hydrogen
butanoic acid
O
H
C
3
electron-attracting
oxygen atom
C
O
H
C
OH
acetic acid
CHEM 102, Fall 2010, LA TECH
acidic hydrogen
3
O
C
H
C
O
3
-
-
C
OH
acetate ion
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Organic or Carboxylic Acids
FCH2CO2H (strongest acid) > ClCH2CO2H > BrCH2CO2H
(weakest acid).
Acid
Ka
pKa
HCOOH (formic acid) 1.78 X 10-43
0.75
CH3COOH (acetic acid) 1.74 X 10-54
0.76
CH3CH2COOH (propanoic acid)1.38 x 10-5 4.86
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Amines
Class of organic bases derived from
ammonia NH3 by replacing hydrogen
by organic groups. They are defined
as bases similar to NH3 by BronstedLowery or Lewis acid/base
definitions.
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Amines
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Acid-Base Chemistry
of Some Antacids
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Acid-Base in the Kitchen
vinegar - acetic acid
lemon juice (citrus juice) - citric acid
baking soda - NaHCO3
milk - lactic acid
baking powder - H2PO4- & HCO3-
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Household Cleaners
A Typical Synthetic Detergent Molecule
H
C
H 2CH2C
H 2CH2C
H 2C
H 2C
H 2C
H 2CH2C
H 2CH2C
H 2
3CH2C
SO3-Na+
Water-soluble part
(hydrophilic)
Oil-soluble part
(hydrophobic)
A nonionic detergent
H
C
H
3(C
H
(C
O
2)4CO
hydrocarbon
chain
(hydrophobic)
CHEM 102, Fall 2010, LA TECH
(
2)2O
CH2C
H
) 2C
H 2C
H 2O
H
2O
alcohol group
(hydrophilic)
ester
link
(hydrophilic)
ether
link
ether
link
(hydrophilic)
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Dishwashing Detergent
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Lewis Definition
G.N. Lewis was successful in including acid and bases
without proton or hydroxyl ions.
Lewis Acid: A substance that accepts an electron pair.
Lewis base: A substance that donates an electron pair.
E.g. BF3(g) + :NH3(g)
F3B:NH3(s)
the base donates a pair of electrons to the acid forming a
coordinate covalent bond common to coordination
compounds. Lewis acids/bases will be discussed later in
detail
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Lewis Acids and Bases Reactions
H+ + NH3  NH4
acid base
Cu+2 + 4 NH3  [Cu(NH3)4+2]
acid
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base
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What acid base concepts
(Arrhenius/Bronsted/Lewis) would
best describe the following reactions:
a) HCl(aq) + NaOH(aq) ---> NaCl(aq) + H2O(l)
b)HCl(g) + NH3(g) --->
NH4Cl(s)
c)BF3(g) + NH3(g) --->
F3B:NH3(s)
d)Zn(OH)2(s) + 2OH-(aq) ---> [Zn(OH)4]2- (aq)
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