intro to acids/bases

Question 1

Bronstead-Lowry acid/base definitions

Answer 1

• acid: H+ donor (needs H with partial positive charge)
• base: H+ acceptor (needs lone pair)
• mostly limited to aqueous reactions!

Question 2

Lewis acid/base definitions

Answer 2

• acid: lone pair acceptor
• base: lone pair donor

Question 3

Ka and pKa

Answer 3

• Ka: equilibrium constant; concentration of products over concentration of reactants
  -pKa: -log (Ka); allows us to compare very small/large Ka values more easily

Question 4

conjugate acid/base pair

Answer 4

differ only by the loss of a H+

Question 5

pKa of different kinds of acids

Answer 5

• very strong: <1
• moderately strong: 1-3
• weak: 3-5
• very weak: 5-15
• extremely weak: <15

Question 6

common strong acids

Answer 6

HCl
HBr
HI
HNO3
H2SO4
HClO4

Question 7

types of acids

Answer 7

• oxyacids: H+ is attached to an oxygen, which is then attached to an electronegative atom or a C=O
• group VI and VII hydrides: H2X or HX
• conjugate acids of weak bases: usually have + charge

Question 8

types of base

Answer 8

• group I and II hydroxides: strong and dissociate completely in water, but not common in organic (we use NaOR often instead)
• amines: weak bases; N with lone pair
• conjugate bases of weak acids: often the anion in salts with the cation as a spectator!

Question 9

ranking of 6 factors for base strength

Answer 9

1. charge
2. resonance
3. size
4. electronegativity
5. induction
6. hybridization

Question 10

charge

Answer 10

• positive charges least likely to give up electrons and are most stable bases
• negative charges most likely to give up electrons and are strongest bases

Question 11

resonance

Answer 11

• more resonance = more spread out electrons = less likely to give up electrons, more stable bases
• less resonance = less spread out electrons = more likely to give up electrons, stronger bases

Question 12

size

Answer 12

• larger atoms have valence electrons more spread out, which means less e- repulsions and more stable bases
• smaller atoms have valence electrons closer together, which means more e- repulsions and stronger bases

Question 13

electronegativity

Answer 13

• greater core charge means electrons are pulled in more tightly = more stable bases
• lower core charge means electrons are pulled in less tightly = stronger bases

Question 14

induction

Answer 14

• distant electronegative atoms cause electrons to be pulled away = less likely to give up electrons, more stable base

*as electronegative atoms move further away from lone pair, base gets stronger

Question 15

hybridization

Answer 15

• sp and sp2 carbons have more electron density closer to nucleus, so less likely to give up electrons and base is more stable
• sp3 carbons have electron density further from the nuleus, so they are more likely to give up electrons and base is stronger

Question 16

nucleophiles and electrophiles

Answer 16

• nucleophile: Lewis base
• electrophile: Lewis acid

Question 17

reaction intermediates

Answer 17

• molecules can get stuck at low-energy minima during multi-step reactions
• sometimes, these last long enough to observe or use (meta-stable)

Question 18

examples of reaction intermediates

Answer 18

***usually Carbon with unusual valencies
- carbocation (C+)
- radicals (7 e-)
- carbanion (C-)