Transcript pK a ~ 3

Polyprotic acids
Since pKa values are
generally wellseparated, only 1 or
2 species will be
present at significant
concentration
H3PO4 + H2O = H2PO4- + H3O+
pKa1 = 2.1
H2PO4- + H2O = HPO42- + H3O+
pKa1 = 7.4
HPO42- + H2O = PO43- + H3O+
pKa1 = 12.7
1
Common acids
HNO3
NO3
Nitric acid
Nitrate
HNO2
NO2
Nitrous acid
Nitrite
H3PO4
PO43
Phosphoric acid
Phosphate
H3PO3
HClO4
ClO4
Perchloric acid
Perchlorate
HClO3
ClO3
Chloric acid
Chlorate
HClO2
ClO2
HPO32
Chlorous acid
Chlorite
Phosphorous acid
Phosphite
HOCl
OCl
H2SO4
SO42
Hypochlorous acid
Hypochlorite
Sulfuric acid
Sulfate
H2SO3
SO32
Sulfurous acid
Sulfite
2
Anhydrides
Ex:
H2O + SO3
=
anhydride
H2SO4
acid form
Acidic
SO3 / H2SO4
“P2O5” / H3PO4
CO2/H2CO3
Basic
Na2O / NaOH
Amphoteric
Al2O3 / Al(OH)3
3
Trends in acidity
4
Pauling’s rules for pKa‘s of oxoacids
1.
Write formula as MOp(OH)q
2.
pKa  8 – 5p
3.
Each succeeding deprotonation increases the pKa by 5
Ex: rewrite HNO3 as NO2(OH)
p = 2;
pKa  8 – 5(2)  2 (exptl value is 1.4)
Ex: rewrite H3PO4 as PO(OH)3
p = 1;
pKa1  8 – 5(1)  3 (exptl value is 2.1)
pKa2  8
(exptl value is 7.4)
pKa3  13
(exptl value is 12.7)
5
pKa values
p
Pauling
pKa
calcn
exptl
Cl(OH)
0
8
7.5
ClO(OH)
1
3
2.0
ClO2(OH)
2
2
1.2
ClO3(OH)
3
7
≈ 10
HlO4 + 2H2O  H5IO6
6
Acid/base chemistry of complexes
Aqueous chemistry:
H2O
Fe(NO3)3 
[Fe(OH2)6]3+(aq) + 3 NO3(aq)
2 [Fe(OH2)6]3+ (aq)
Hexaaquairon(III), pKa ~ 3
= [Fe2(OH2)10OH]5+ (aq) + H3O+(aq)
dimer
7
Lewis acids and bases
A
LA
+ :B =
LB
A:B
complex
LA = e pr acceptor; LB = e pr donor
Lewis definition is more general than BL definition, does not require
aqueous or protic solvent
Ex:
6 :CO

=
[W(CO)6]
BCl3 + :OEt2
=
BCl3:OEt2
W +
Fe3+(g) +
6 :OH2 → [Fe(OH2)6]3+
8
log K and ligand type
9