Acid-Base Chemistry
Sept 21
Chapter 6:206
6:206-215
215
HW: 27, 28, 29, 30, 31, 32, 33, 36
Frustrated Lewis Pairs(#36): J. Am. Chem.
Soc., 2009, 131 (29), pp 9918–9919
Goals: Predict pKa using periodic trends,
structures; solvent levelling
What happens when chemical compounds
are added to water?
2 ... - 6 6 6UMass
6 6 Amherst
Created by Karsten Theis
Size and # lp governs acidity in binary hydrides
- 6 6 6 6 6 2 ... 2
Question!
Which reason explains why HF is a stronger acid
than CH4?
A) electronegativity of the E-H bond
B) delocalizing negative charge in the conjugate
base
C) the octet rule of the conjugate base
D) expanded octet for the binary hydride
E) Atomic radius of the central atom
- 6 6 6 6 6 2 ... 3
Which statements are correct?
1)
2)
3)
4)
pKa rank is HClO4 < HClO3 < HClO2 < HOCl
All shown Lewis structures are correct
All shown Lewis structures are incorrect
Delocalized charge in conjugate base dictates
pKa ranking
A) 1
B) 1
C) 2
D) 3
E) 1
and
and
and
and
and
2
3
4
4
4
- 6 6 6 6 6 2 ... 4
Which statements are correct?
1)
2)
3)
4)
pKa rank is HClO4 < HClO3 < HClO2 < HOCl
All shown Lewis structures are correct
All shown Lewis structures are incorrect
Delocalized charge in conjugate base dictates
pKa ranking
A) 1 and 2
B) 1 and 3
C) 2 and 4
D) 3 and 4
E) 1 and 4
pKa ~ 9 – 7n
n = # pi-bonded O-atoms
- 6 6 6 6 6 2 ... 5
H+ is a hard acid; so is Fe3+
- 6 6 6 6 6 2 ... 6
Rank the Ksp for these transition metal species in
water, and the reason why
A) Mg(OH)2 < Fe(OH)3 < Fe(OH)2 < Zn(OH)2
Due to χ of cation
B) Fe(OH)3 < Mg(OH)2 < Fe(OH)2 < Zn(OH)2
Due to Q/r of cation
C) Zn(OH)2 < Fe(OH)2 < Mg(OH)2 < Fe(OH)3
Due to delocalized charge on lone pairs
D) Mg(OH)2 < Fe(OH)3 < Fe(OH)2 < Zn(OH)2
Due to reduction potentials
E) Mg(OH)2 < Fe(OH)2 < Zn(OH)2 < Fe(OH)3
Due to covalent bonding
- 6 6 6 6 6 2 ... 7
Solvent Leveling Effects: from the conjugate acid or
base of the solvent.
In H2O, the pKa trend of HX is HI = HBr = HCl <
HF
‘strong’ acids form H3O+ (stronger than H3O+)
(Is H2O a conjugate acid or base?)
In glacial acetic acid (H3CCOOH), the pKa trend is
HI < HBr < HCl < HF
‘strong’
strong acids form H3CCOOH2+ (stronger than
H3CCOOH2+)
- 6 6 6 6 6 2 ... 8