Chemistry 281(01) Winter 2014
CTH 277 10:00-11:15 am
Instructor: Dr. Upali Siriwardane
E-mail: upali@latech.edu
Office: 311 Carson Taylor Hall ; Phone: 318-257-4941;
Office Hours: MTW 8:00 am - 10:00 am;
TR 8:30 - 9:30 am & 1:00-2:00 pm.
January 16, 2014 Test 1 (Chapters 1&,2),
February 6, 2014 Test 2 (Chapters 3 &4)
February 25, 2014, Test 3 (Chapters 4 & 5),
Comprehensive Final Make Up Exam: February 27, 2012 9:3010:45 AM, CTH 311.
What are Acids &Bases?
Definition?
a) Arrhenius
b) Bronsted-Lowry
c) Lewis
CHEM 281 Winter 2014
2
Arrhenius definitions
Acid Anything that produces hydrogen
ions in a water solution.
HCl (aq)
H+ + Cl-
BaseAnything that produces hydroxide
ions in a water solution.
NaOH (aq)
Na+ + OH-
Arrhenius definitions are limited to aqueous
solutions.
Acid base reactions:
HCl(aq) + NaOH(aq)
CHEM 281 Winter 2014
NaCl(aq) + H2O(l)
3
Brønsted-Lowry definitions
Expands the Arrhenius definitions
Acid
Proton donor
Base
Proton acceptor
This definition explains how substances like
ammonia can act as bases.
NH3(g) + H2O(l)
NH4+ + OH-
Eg. HCl(g) + NH3(g) ------> NH4Cl(s)
HCl (acid), NH3 (base).
CHEM 281 Winter 2014
Chapter 4-4
Proton in water
CHEM 281 Winter 2014
Chapter 4-5
Dissociation Equilibrium
HCl(aq) + H2O(l)
H2SO4(aq) + H2O(l)
H3+O(aq) + Cl-(aq)
H3+O(aq) + HSO4-(aq)
H2O(l) + H2O(l)
H3+O(aq) + OH-(aq)
This dissociation is called autoionization of water.
HC2H3O2(aq) + H2O(l)
NH3 (aq) + H2O(l)
CHEM 281 Winter 2014
H3+O(aq) + C2H3O2-(aq)
NH4+ + OH-(aq)
Chapter 4-6
Bronsted conjugate acid/base pairs in
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 281 Winter 2014
Chapter 4-7
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 281 Winter 2014
H3O+
H2O
HC2H3O2
C2H3O2-
NH4+
NH3
H2SO4
HSO4-
HSO4-
SO42Chapter 4-8
Select acid, base,
acid/conjugate base pair,
base/conjugate acid pair
H2SO4(aq) + H2O(l)
acid
base
conjugate acid
conjugate base
base/conjugate acid pair
acid/conjugate base pair
CHEM 281 Winter 2014
H 3+O(aq) + HSO4-(aq)
Chapter 4-9
Types of Acids and Bases
Binary acids
Oxyacid
Organic acids
Acidic oxides
Basic oxides
Amine
Polyprotic acids
CHEM 281 Winter 2014
Chapter 4-10
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
CHEM 281 Winter 2014
Chapter 4-11
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
CHEM 281 Winter 2014
Chapter 4-12
Aqua Acids
Acidic proton is on a water molecule coordinated
to a central metal ion
[Fe(OH2)6]3+,Al(OH2)63+, Si(OH)4
Acidity increase with charge
Acidity increase as metal become smaller
CHEM 281 Winter 2014
Chapter 4-13
Anhydrous oxides
The Lux/Flood Definition
Covers things which would become acids or
bases if dissolved in water.
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
CHEM 281 Winter 2014
Chapter 4-14
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
CHEM 281 Winter 2014
Chapter 4-15
Protic Acids
Monoprotic Acids: The form protic refers
to acidity or 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.
CHEM 281 Winter 2014
Chapter 4-16
Amines
Class of organic bases derived from
ammonia NH3 by replacing hydrogen
by organic groups. They are defined
as bases similar to NH3 by Bronsted
or Lewis acid/base definitions.
CHEM 281 Winter 2014
Chapter 4-17
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)
CHEM 281 Winter 2014
Chapter 4-18
Common acids and bases
Acids
nitric
hydrochloric
sulfuric
acetic
Bases
ammonia
sodium hydroxide
Formula Molarity*
HNO3 16
HCl
12
H2SO4
18
HC2H3O2
18
NH3(aq)
NaOH
15
solid
*undiluted.
CHEM 281 Winter 2014
Chapter 4-19
Acids and bases
Acidic
– Citrus fruits
– Aspirin
– Coca Cola
– Vinegar
– Vitamin C
CHEM 281 Winter 2014
Basic
Baking soda
Detergents
Ammonia cleaners
Tums and Rolaids
Soap
Chapter 4-20
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
B+ + OH[H3+O][ A-]
[B+ ][OH-]
Ka = --------------- ; Kb = ----------------[HA]
[BOH]
CHEM 281 Winter 2014
Chapter 4-21
What is Ka
HCl(aq) + H2O(l) <===> H3+O(aq) + Cl-(aq)
CHEM 281 Winter 2014
Chapter 4-22
E.g. Ka
HCl(aq) + H2O(l)
H3+O(aq) + Cl-(aq)
Ka=
[H3+O][Cl-]
----------------[HCl]
Ka=
[H+][Cl-]
----------------[HCl]
CHEM 281 Winter 2014
Chapter 4-23
What is Ka1 and Ka2?
H2SO4(aq) + H2O(l)
H3+O(aq) + HSO4-(aq)
HSO4-(aq) + H2O(l)
H3+O(aq) + SO42-(aq)
CHEM 281 Winter 2014
Chapter 4-24
What is Kb
NH3 (aq) + H2O(l)
CHEM 281 Winter 2014
NH4+ + OH-(aq)
Chapter 4-25
H2SO4 Dissociation
E.g.
H2SO4(aq) + H2O(l)
HSO4-(aq) + H2O(l)
H3+O(aq) + HSO4-(aq)
H3+O(aq) + SO42-(aq)
[H3+O][HSO4-]
H2SO4 ; Ka1 = ------------------[H2SO4]
[H3+O][SO42-]
H2SO4 ; Ka2 = ------------------[HSO4-]
CHEM 281 Winter 2014
Chapter 4-26
Ka and Kb
E.g.
HC2H3O2(aq) + H2O(l)
H3+O(aq) + C2H3O2-(aq)
[H+][C2H3O2-]
H C2H3O2; Ka= -----------------[H C2H3O2]
NH3 (aq) + H2O(l)
NH4+ + OH-(aq)
[NH4+][OH-]
NH3; Kb= -------------[ NH3]
CHEM 281 Winter 2014
Chapter 4-27
Acidity/Basicity of HA and F-
CHEM 281 Winter 2014
Chapter 4-28
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.
Chapter 4-29
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.
Chapter 4-30
Autoionization of water
Autoionization When water molecules react with
one another to form ions.
H2O(l) + H2O(l)
H3O+(aq) + OH-(aq)
(10-7M)
Kw
=[
H3O+ ]
[
(10-7M)
OH- ]
ion product
of water
= 1.0 x 10-14 at 25oC
Note: [H2O] is constant and is included in Kw.
Chapter 4-31
What is Kw?
H2O(l) + H2O(l)
H3+O(aq) + OH-(aq)
This dissociation is called autoionization of
water.
Autoionization of water:
Kw = [H3+O][OH-]
Kw is called ionic product of water
Kw = 1 x 10-14
CHEM 281 Winter 2014
Chapter 4-32
Why is water important for acid/base
equilibria?
Water is the medium/solvent for acids and
bases.
Acids and bases alter the dissociation
equilibrium of water based on Le Chaterlier’s
principle
H2O(l) + H2O(l)
CHEM 281 Winter 2014
H3+O(aq) + OH-(aq)
Chapter 4-33
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 281 Winter 2014
Chapter 4-34
pH and other “p” scales
We need to measure and use acids and bases
over a very large concentration range.
pH and pOH are systems to keep track of
these very large ranges.
– pH
– pOH
– pH + pOH
CHEM 281 Winter 2014
= -log[H3O+]
= -log[OH-]
= 14
Chapter 4-35
pH scale
A logarithmic scale used to keep track of the
large changes in [H+].
14
10-14 M
Very
Basic
7
0
10-7 M
Neutral
1M
Very
Acidic
When you add an acid, the pH gets smaller.
When you add a base, the pH gets larger.
CHEM 281 Winter 2014
Chapter 4-36
pH of some common materials
Substance
pH
1 M HCl
Gastric juices
Lemon juice
Classic Coke
Coffee
Pure Water
Blood
Milk of Magnesia
Household ammonia
1M NaOH
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
CHEM 281 Winter 2014
Chapter 4-37
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 281 Winter 2014
Chapter 4-38
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 281 Winter 2014
Chapter 4-39
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 Ionize completely in water.
Strong bases are metal
hydroxides - NaOH, KOH
• Weak bases Partially ionize in water.
CHEM 281 Winter 2014
Chapter 4-40
pH and pOH calculations of acid and
base solutions
a) Strong acids/bases
dissociation is complete for strong
as HNO3 or base NaOH
acid such
[H+] is calculated from molarity (M) of the solution
b) weak acids/bases
needs Ka , Kb or percent(%)dissociation
CHEM 281 Winter 2014
Chapter 4-41
Titration curves
Overtitration
Indicator
Transition
pH
Equivalence
Point
Buffer region
CHEM 281 Winter 2014
% titration or ml titrant
Chapter 4-42
Indicators
Acid-base indicators are highly colored weak
acids or bases.
HIn
In+ H+
color 1
color 2
They may have more than one color transition.
Example. Thymol blue
Red - Yellow - Blue
One of the forms may be colorless phenolphthalein (colorless to pink)
CHEM 281 Winter 2014
Chapter 4-43
Selection of an indicator for a
titration
a) strong acid/strong base
b) weak acid/strong base
c) strong acid/weak base
d) weak acid/weak base
Calculate the pH of the solution at he
equivalence point or end point
CHEM 281 Winter 2014
Chapter 4-44
Common Ion Effect
Weak acid and salt solutions
E.g. HC2H3O2 and NaC2H3O2
Weak base and salt solutions
E.g. NH3 and NH4Cl.
H2O + C2H3O2- <==> OH- + HC2H3O2
(common ion)
H2O + NH4+
<==> H3+O + NH3
(common ion)
CHEM 281 Winter 2014
Chapter 4-45
Buffers
Solutions that resist pH change when small
amounts of acid or base are added.
Two types
weak acid and its salt
weak base and its salt
HA(aq) + H2O(l)
H3O+(aq) + A-(aq)
Add OHAdd H3O+
shift to right
shift to left
Based on the common ion effect.
CHEM 281 Winter 2014
Chapter 4-46
Buffers
The pH of a buffer does not depend on the absolute
amount of the conjugate acid-base pair. It is based
on the ratio of the two.
Henderson-Hasselbalch equation.
Easily derived from the Ka or Kb expression.
Starting with an acid
[A-]
pH = pKa + log [HA]
Starting with a base
[HA]
pH = 14 - ( pKb + log [A-] )
CHEM 281 Winter 2014
Chapter 4-47
Buffers and blood
• Control of blood pH
Oxygen is transported primarily by hemoglobin in
the red blood cells.
CO2 is transported both in plasma and the red
blood cells.
CO2 (aq) + H2O
H2CO3 (aq)
The bicarbonate
buffer is essential
for controlling
blood pH
CHEM 281 Winter 2014
H+(aq) + HCO3-(aq)
Chapter 4-48
Main Group Acid/Bases
CHEM 281 Winter 2014
Chapter 4-49
Amphoteric Oxides
CHEM 281 Winter 2014
Chapter 4-50
Strength of oxo-acids by Paulings Rules
For OpE(OH)q, pKa ~ 8 - 5p
The successive pKa values of polyprotic acids (i.e.
q >1) increase by 5 units for each successive
proton transfer.
CHEM 281 Winter 2014
Chapter 4-51
pKa Values of Oxy Acids
CHEM 281 Winter 2014
Chapter 4-52
Lewis Definition
• 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)
CHEM 281 Winter 2014
F3B:NH3(s)
Chapter 4-53
Lewis Acids/Bases
CHEM 281 Winter 2014
Chapter 4-54
Hard and soft acids and bases
CHEM 281 Winter 2014
Chapter 4-55
Solvent leveling
• If the solvent contains ionizable protons it is said
to be protonic, and if it is protonic, it will engage
in acid-base reactions.
• All acids/bases which are stronger than the
H3O+(aq) or OH-(aq) ion will react to produce
hydronium/hydroxide ion, and so their strength
will be leveled to that of the H3O+(aq) or OH-(aq)
ion.
• In aqueous solution, the strongest acid/base
which can exist is the H3O+(aq) or OH-(aq)
CHEM 281 Winter 2014
Chapter 4-56
Acid-Base Discrimination Windows
CHEM 281 Winter 2014
Chapter 4-57
Levelling effect in other protic liquid
all acids are levelled to the strength of the
ammonium ion, NH4+, and all bases are levelled
to the strength of the amide ion, NH2-.
2 NH3
NH4+ + NH2-.
2HNO3
H2NO3+ + NO23HF
H2F+ + HF22H2SO4
H3SO4+ + HSO4CHEM 281 Winter 2014
Chapter 4-58
Polycation Formation
NaAl13O4(OH)24(H2O)12(SO4)4 .x H2O
CHEM 281 Winter 2014
Chapter 4-59
Polyanion Formation:Zeolites
The general method of zeolite production
involves dissolving an aluminium source
(metal or oxide) into an aqueous solution
of sodium or potassium hydroxide. Once
this solution has cooled the silica source
(and organic template, if required) is added
in The form of an aqueous slurry and the
resulting gel stirred until homogenous.
Na12[(AlO2)12(SiO2)12.27H2O
CHEM 281 Winter 2014
Chapter 4-60