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Optional Comprehensive Final Exam: November 15, 2012 :
Chapters 13, 14, 15, 16, 17, and 18
Chemistry 102(001) Fall 2012
16-2CHEM 102, Fall 2012, LA TECH
Chapter 16. Acids and Bases
16.1 The Brønsted-Lowry Concept of Acids and Bases
16.2 Types of acids/bases:Organic Acids and Amines
16.3 The Autoionization of Water
16.4 The pH Scale
16.5 Ionization Constants of Acids and Bases
16.6 Problem Solving Using Ka and Kb
16.7 Molecular Structure and Acid Strength
16.8 Acid-Base Reactions of Salts
16.9 Practical Acid-Base Chemistry
16.10 Lewis Acid and Bases
16-3CHEM 102, Fall 2012, LA TECH
Types of Reactionsa) Precipitation Reactions. Reactions of ionic compounds or
saltsb) Acid/base Reactions. Reactions of acids and basesc) Redox Reactions. reactions of oxidizing & reducing
agents
16-4CHEM 102, Fall 2012, LA TECH
What are Acids &Bases?
Definition?
a) Arrhenius
b) Bronsted-Lowry
c) Lewis
16-5CHEM 102, Fall 2012, LA TECH
Arrhenius, Svante August (1859-1927), Swedish chemist, 1903 Nobel Prize in chemistry
•Acid Anything that produces hydrogen ions in a water solution.
HCl (aq) H+
( aq) + Cl-
( aq)
•Base Anything that producs hydroxide ions in a water solution.
NaOH (aq) Na+
( aq) + OH
- ( aq)
•Arrhenius definitions are limited proton acids and hydroxide bases
to aqueous solutions.
Arrhenius Definitions
16-6CHEM 102, Fall 2012, LA TECH
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) NH4+
+ OH-
Brønsted-Lowry definitions
16-7CHEM 102, Fall 2012, LA TECH
Lewis DefinitionG.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
16-8CHEM 102, Fall 2012, LA TECH
1) Acids and bases can be defined in several ways. Which definitions of the bases that fits the description below?
a) a compound that produces more OH- ions in water:
b) a proton acceptor:
c) an electron pair donor:
16-9CHEM 102, Fall 2012, LA TECH
Types of Acids and Bases
Binary acids
Oxyacid
Organic acids
Acidic oxides
Basic oxides
Amine
Polyprotic acids
16-10CHEM 102, Fall 2012, LA TECH
Types of Acids and BasesBinary acids: HCl, HBr, HI, H2S
More than two elements: HCN
Oxyacid: HNO3, H2SO4, H3PO4
Polyprotic acids: H2SO4, H3PO4
Organic acids: R-COOH, R= CH3-, CH3CH2-
Acidic 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
16-11CHEM 102, Fall 2012, LA TECH
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 waterSO3 + H2O ---> H2SO4
CO2 + H2O ---> H2CO3
NO2 + H2O ---> HNO3
16-12CHEM 102, Fall 2012, LA TECH
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
16-13CHEM 102, Fall 2012, LA TECH
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.
16-14CHEM 102, Fall 2012, LA TECH
Polyprotic Acidsacids where more than one hydrogen per molecule
is released
16-15CHEM 102, Fall 2012, LA TECH
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-Lowery or Lewis acid/base definitions.
16-16CHEM 102, Fall 2012, LA TECH
Amines
16-17CHEM 102, Fall 2012, LA TECH
2) Identify types of acids/bases as: binary acids, oxy acids, organic acids, acidic oxides, basic oxides, amine and polyprotic acids.
a) HF b) HBr c) H3PO4
d) H2SO4 e) HNO3 f) R-COOH
g) NO2 h) SO3 j)CaO
k) R-NH2
16-18CHEM 102, Fall 2012, LA TECH
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
16-19CHEM 102, Fall 2012, LA TECH
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
16-20CHEM 102, Fall 2012, LA TECH
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
16-21CHEM 102, Fall 2012, LA TECH
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
16-22CHEM 102, Fall 2012, LA TECH
< <<
<
Oxo Acid
16-23CHEM 102, Fall 2012, LA TECH
3) Which of the following is stronger acid or base:
a) H2SO4 or H2SO3:
b) HCl or HI:
c) HClO or HClO3:
d) H2S or HF:
e) CF3COOH or CH3COOH:
f) CH3COOH or CH3CH2COOH
16-24CHEM 102, Fall 2012, LA TECH
DissociationStrong 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
16-25CHEM 102, Fall 2012, LA TECH
4) Write equations for the dissociation equilibrium reactions for the following acids and bases in water. Which of these are acid or dissociations?
a) HCl:
b) H2SO4 :
16-26CHEM 102, Fall 2012, LA TECH
4) Write equations for the dissociation equilibrium reactions for the following acids and bases in water. Which of these are acid or dissociations?
c) H2O (autoionization): What is auto ionization?
d) HC2H3O(acetic acid):
e) NH3:
16-27CHEM 102, Fall 2012, LA TECH
Bronsted acid/conjugate base and base/conjugate acid pairs inacid/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
16-28CHEM 102, Fall 2012, LA TECH
Conjugate acid-base pairs.
Acids and bases that are related by loss or gain of H+ as H3O+
and H2O.
Examples. Acid Base
H3O +
H2O
HC2H3O2 C2H3O2-
NH4 +
NH3
H2SO4 HSO4-
HSO4- SO4
2-
Brønsted-Lowry Definitions
16-29CHEM 102, Fall 2012, LA TECH
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
16-30CHEM 102, Fall 2012, LA TECH
5) For HOCl write:
a) Dissociation equilibrium reaction for the HOCl:
b) Identify the acid/conjugate base pair:
c) Identify the base/conjugate acid pair:
d) The equilibrium constant expression:
16-31CHEM 102, Fall 2012, LA TECH
Strong Acid vs. Weak AcidsStrong acidcompletely ionizedHydrioidic HI Ka ~ 1011 pKa = -11Hydrobromic HBr Ka ~ 109 pKa = -9Perchloric HClO4 Ka ~ 107 pKa = -7Hyrdrochloric HCl Ka ~ 107 pKa = -7Chloric HClO3 Ka ~ 103 pKa = -3Sulfuric H2SO4 Ka ~ 102 pKa = -2Nitric HNO3 Ka ~ 20 pKa = -1.3Weak acidpartially ionizedHydrofluoric acid HF Ka = 6.6x10-4 pKa = 3.18Formic acid HCOOH Ka = 1.77x10-4 pKa = 3.75Acetic acid CH3COOH Ka = 1.76x10-5 pKa = 4.75Nitrous acid HNO2 Ka = 4.6x10-4 pKa = 3.34Acetyl Salicylic acid C9H8O4 Ka = 3x10-4 pKa = 3.52Hydrocyanic acid HCN Ka = 6.17x10-10 pKa = 9.21
16-32CHEM 102, Fall 2012, LA TECH
Strong Base vs. Weak BaseStrong Basecompletely ionizedLithium hydroxide LiOHSodium hydroxide NaOH