acids and bases arrhenius bronsted-lowry lewis. definitions of acids/bases
TRANSCRIPT
Acids and Bases
Arrhenius
Bronsted-Lowry
Lewis
Definitions of Acids/Bases
Arrhenius acid - forms H3O+ in H2O
Bronsted-Lowry acid - donates a H+ (proton)
Lewis acid - accepts an electron pair to form a new bond
Arrhenius base - forms OH - in H2O
Bronsted-Lowry base - accepts a H + (proton)
Lewis base - donates an electron pair to form a new bond
Measuring Acid StrengthKa
Acid Strength defined by pKa
HCl + H2O H3O + Cl
Keq = [H3O ][Cl ]
[HCl][H2O]
Ka = Keq[H2O] =[H3O ][Cl ]
[HCl]= 10
7
pKa = -log(Ka) = -7
Dissociation in H2OArrhenius Acid forms H3O+
Bronsted-Lowry Acid donates a H+
Resonance Stabilization
C C
O
OH
H
HH
pKa 4.7
+ NaHCO3 HH
H
C
O
OC
HH
H
C
O
OC
H2CO3 + Na
HH
H
C C
O
O
resonance hybrid
Na
Stronger Acid Controls Equilibrium
HCl + H2O H3O + Clacid base conjugate conjugate
acid base
pKa = -7 -1.7 stronger weaker
Reaction Described with ArrowsHCl donates a protonH2O accepts a proton
H Cl + OHH O
H
HH+ Cl
Equilibrium Reactions
Draw the Conjugate Acid and Base
CH3CH2CH2OH + H2SO4
Propanol is a Base
base acid+ HSO4
H
CH3CH2CH2OHH2SO4+CH3CH2CH2OH
Draw the Conjugate Acid and Base
CH3CH2CH2OH + Na NH2
Propanol is an Acid
CH3CH2CH2O + Na NH2H CH3CH2CH2O Na
+ NH3
acid base
c.a.
c.b.
Some Acid-Base Reactions
The Effect of Resonance on pKa
Identify the Acid and Base
CH3OH + OCOH
O
CH3O + HOCOH
O
Equilibrium Favors Reactants
CH3OH + OCOH
O
CH3O + HOCOH
O
acid base conj. base conj. acid
pKa 15.5 6.5
Carboxylic Acids can be Separated from non-acidic
Compounds OCCH3
O
C
O
OH
Aspirin
+ Na OH
OCCH3
O
C
O
O Na
+ H2O
NaOCCH3
O
C
O
O
acid base conj. base conj. acid
HCl
Lewis Acids and Bases
B H B H
base acid complex
arrow always goes from the base to the acid always originate your arrow at the e- donor
Formation of a new bond
BH3 + NH3 B
H
H
H
N H
H
Hacid base
CH3CH
O
+ AlCl3
OAlCl3
CH3CH
base acid complex
complex
Lewis Base = NucleophileLewis Acid = Electrophile
Draw the Acid-Base Complexes
CH3OCH3 + FeCl3
CH3+ + H2O
HOC(CH3)3 + AlCl3
a)C C
C O
H
H
H
H H
HC
C O
H
HH
C
b)
+
c)
OH
H
N
+
LiO Li
+N
H
CH3
C
O
C
H
HO
H
HH
C
O
C
H
HH
CH3 + H2O
HK
K
+ H2
a)C C
C O
H
H
H
H H
HC
C O
H
HH
C
b)
+
c)
OH
H
N
+
LiO Li
+N
H
CH3
C
O
C
H
HO
H
HH
C
O
C
H
HH
CH3 + H2O
HK
K
+ H2
a) C C
C O
H
H
H
HH3N
H
HC
C O
H
H
CH3N
b) CH3O
+
+ Br
c)
C C
BrH
HH
H
HH
H
CH
HC
CH3
H
+ CH3OH
BCl
Cl
ClBCl3 + N
CH3
CH3H
CH3
CH3HN
Draw Arrows
a) C C
C O
H
H
H
H
H3N
H
HC
C O
H
H
CH3N
b) CH3O+ Br
c)
C C
BrH
HH
H
HH
H
CH
HC
CH3
H
+ CH3OH
BCl
Cl
N
HClBCl3 + HN
Identify the Conjugate Base(i.e. Which H is most acidic?)
+ Na NH2NH3 +
a
b
c
d
eC6H7ONa
C H
OH
H
HH
H
H
H
By deprotonating one of the Hb protons, one can distribute the charge onto three atoms and give a major resonance structure with the charge on the Oxygen (the third structure).
C H
OH
H
HH
H
H
H
e
d
c
b
a
C H
OH
HH
H
H
H
e
d
c
b
a
C H
OH
HH
H
H
H
e
d
c
b
a
C H
OH
H
HH
H
H
HC6H7ONa+ Na NH2
NH3 +
a
b
c
d
e