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ACID-BASE CEMISTRY
Acid-Based Concepts
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Acid-Base Concepts
The definitions of an acid and a baserange from proton and hydroxide donors
to electron pair donors and acceptorsto specialized definitions for non-solvent
systems.
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Acid-Base Definitions
Arrhenius - Acids are proton donors,bases are hydroxide donors.
Bronsted-Lowry - Acids are proton donors,bases are proton acceptors.
Lux-Flood - Acids are oxide acceptors,bases are oxide donors.
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Lux-Flood ReactionsAcids are oxide acceptors, bases are oxide donors
CaO + SiO2 CaSiO3
CaO + H2O Ca2+ + 2 OH-
base acid
basicanhydride
SiO2 + H2O H2SiO3
acidicanhydride
Acid-Base DefinitionsDon’t Have To Be Limited to H & O
(CH3)4N+ Cl- bases are chloride donors
FeCl3 acids are chloride acceptors
OPCl3or
OP(OEt)3
(CH3)4N+ Cl- + FeCl3 (CH3)4N
+ + FeCl4-
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Solvent SystemsAutoionization
2 H2O H3O+ + OH-
2 NH3 NH4+ + NH2
-
2 OPCl3 OPCl2+ + OPCl4
-
strongest acidallowed in
solvent
strongest baseallowed in
solvent
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Solvent SystemsAcid Leveling
2 H2O H3O+ + OH-
acids stronger than H3O+
are leveled to H3O+
bases stronger than OH-
are leveled to OH-
HNO3 + H2O H3O+ + NO3
-
CaO + H2O Ca2+ + 2 OH-
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Solvent SystemsAcid Leveling
3 HF H2F+ + HF2
-
What is the strongest acid andthe strongest base allowed in
liquid hydrofluoric acid?
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Other Acid-Base Definitions
Lewis - Acids are electron pair acceptor,bases are electron pair donors.
Usanovich - Acids are negative charge acceptors,bases are negative charge donors.
metalloids areamphoteric
General Acid-Base Concepts
more
basi
c
metal oxides are basic
nonmetal oxidesare acidic
General Acid-Base Concepts
Beryllium oxide is amphoteric
high charge density causes polarizationof any electron source
BeO is more acidic and less basic thanother alkaline earth oxides.
BeO + 2 H+ Be2+ + H2O
BeO + H2O + 2 OH- Be(OH)42-
General Acid-Base ConceptsHydration and Hydrolysis
coordination of the solvent (solvation)releases energy and stabilizes the product
high charge density ions have large hydration (solvation) energies
Na+ + n H2O [Na(H2O)n]+
General Acid-Base ConceptsHydration and Hydrolysis
Al3+ + 6 H2O [Al(H2O)6]3+
If the cation is acidic enough, it canpolarize the oxygen of water away fromthe hydrogen.
[Al(H2O)5 (OH)]2+ + H3O+
H2O
the pH of0.1 M Al(NO3)3
is 3.07
Why is 0.1 M iron(III) ion even more acidic?
General Acid-Base ConceptsOxyacids
HmXOn The acidity of oxyacids depends on
formal charge on the central atom
inductive effects of substituents
charge on the complex
General Acid-Base ConceptsOxyacids
HmXOn if n-m 2, strong acid pKa << 0= 1, weak acid pKa 2.1 ± 0.9= 0, very weak acid pKa 8.5 ± 1
sequential proton loss leads topK2 values of +5 greater
Examples: HNO3
HNO2
HSO4-
HClO2
H3PO4
H2PO4-
HClO3
HClO
HNO3
HNO2
HSO4-
HClO2
H3PO4
H2PO4-
HClO3
HClO
<< 0
3.3
1.9
HClO2
2.1
7.2
HClO3
7.5
General Acid-Base ConceptsOxyacids
HmXOn The acidity of oxyacids depends on
formal charge on the central atom
inductive effects of substituents
charge on the complex
pKa = 10.5 - 5.0 n - x for X(OH)mOn
General Acid-Base ConceptsOxyacids
Special Cases
H2SO3 pKa = 1.81
H3PO3 pKa = 2.00
H2CO3 pKa = 6.37
H3BO3 pKa = 9.1
General Acid-Base ConceptsSubstituted Amines
NR3 The basicity of amines depends on
inductive effects of substituents
steric effects
NF3
no basiccharacter
NH3 NH2CH3 NH(CH3)2 N(CH3)3
4.74
pKb
3.36 3.29 4.28
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