Chapter 2: 2.2 Factors Influencing Acid/Base Strength

Question 1

What types of conjugate bases will strong and weak acids make?

Answer 1

1. Strong acids make weak/stable conjugate base
2. Weak acids make strong/unstable conjugate base

Question 2

What factors influence acid/base strength?

Answer 2

1. Electronegativity
2. Atom size
3. Resonance
4. Hybridization
5. Induction
6. Aromaticity

Question 3

Define:

Electronegativity

Answer 3

A measure of how well an atom hold electrons to its nucleus (in a bond)

Question 4

In an acid:

What effect does a more electronegative “A” in HA have on the A- and the acid?

Answer 4

The more stable the A- and the stronger the acid

Question 5

State:

The effect of atom size on acid strength

Answer 5

The larger the “A” in HA, the more stable the A- and the stronger the acid

Question 6

When is the atom size considered in acid strength?

Answer 6

Most commonly considered when thinking about the mineral acids

Question 7

How do resonance structures stabilize A- in HA?

Answer 7

Delocalize the negative charge on multiple atoms

Question 8

What effect does resonance have on acid strength?

Answer 8

If A- has resonance, HA is more acidic

Question 9

What effect does hybridization have of acid strength?

Answer 9

The more s-character that the “A” in HA has, the more stable the A- and the stronger the acid

Question 10

Define:

S-character

Answer 10

The percentage of s in the hybrid orbital (sp = 50% s, sp2 = 33% s etc.)

Question 11

What effect does hybridization have on base strength?

Answer 11

If the lone pair is in an orbital with more s-character, it will be lower in energy, more stable, and less likely to get protonated
* That’s why amines are generally more basic than imines and nitriles

Question 12

What effect does induction have on acid strength?

Answer 12

Inductive stabilization is less important than resonance for A- stabilization
* The presence of an electronegative atom on A- stabilizes A- and means HA is a stronger acid

Question 13

What are 3 factors we need to consider with induction?

Answer 13

1. Electronegativity of X: The more electronegative X is, the stronger acid HA will be
2. Proximity of X: The closer X is to the negatively charged atom, the stronger acid HA will be
3. Number of X atoms: The more atoms there are, the stronger acid HA will be

Question 14

What effect does aromaticity have on acid strength?

Answer 14

If an anion is aromatic it will be stable, and thus the acid will be stronger

Question 15

What effect does aromaticity have on base strength?

Answer 15

If a lone pair of electrons is necessary for a compound to be aromatic, it will less likely get protonated