Chem. 17 - Chpt. 8 Reading Notes

Front 1

What are Bronsted Acids and Bases?

Back 1

Bronsted Acid - tendency to lose a proton, (H)
Bronsted Bases - tendency to accept a proton, (H)

Front 2

If the value of delta G is very negative, in which direction is equilibrium favored?

Back 2

Large delta G ~ equilibrium lies well over to the right

Front 3

What is a zwitterion? Draw and example.

Back 3

A zwitterion is a neutral species that contains goth a positive and a negative charge.

Ex.: B-15

Front 4

What is the pH a measure of in a solution?

Back 4

pH is a measure of the acididty of a solution.

Front 5

What is the equation relating pH and H3O+?

Back 5

pH = -log[H3O+]

(pKa = -log[Ka])

Front 6

What is the equation frot he ionization constant in water?

Back 6

Kw = [H3O+][OH-] = 10^-14 mol^2dm^-6

Front 7

For a strong acid in an aqueous solution, does equilibrium lie to the left or to the right?

Back 7

Right

Front 8

In a mixture of acid in an aqueous solution, what happens to the solubility as pH is lowered? How does this relate to aspirin in the stomach?

Back 8

pH is lowered ~ acidic for present increases ~solubility decreases

In the acidic environment of hte stomach, soluble aspirin is converted back to the normal acidic form and precipitates out of solution.

Front 9

What is the equation that relates pH and pKa?

Back 9

pH = pKa + log([A-]/[AH])

Front 10

Acids are dissolved by raising/lowering pH; bases are dissolved by raising/lowering pH.

Back 10

Acids are dissolved by raising pH. Bases are dissolved by lowering pH.

Front 11

Using the relationship between solubility and pH, how can organic acids be separated from mixtures of other compounds?

Back 11

Dissolve the mixture of compounds in dichloromethane, (which is immiscible with water ~separates into different layer),a nd 'wah'this solution with aqueous sodium hydroxide, any organic acids present will be converte do their water-soluble wsalts and sissolve into the water layer.

Front 12

Is anionic A- more or less soluble in water than a neutral acid?

Back 12

A- is more soluble

Front 13

Is a netural acid more or less soluble in organic solvents than anionic A-?

Back 13

Neutral acids are more soluble - the more neutral, the closer to organic solvents ~ the more soluble

Front 14

Is a cationic acid, (HB+), more or less table in water than the neutral conjugate base B?

Back 14

HB+ is more soluble

Front 15

Is a neutral conjugate base, (B), more or less soluble in organic solvents than the cationic acid, (HB+)

Back 15

Neutral conjugate base is more soluble

Front 16

What does an acid's pKa depend on?

Back 16

Acid's pKa depends on the stability of its conjugate base.

Front 17

The stronger the acid, the stronger/weaker its conjugate base?

Back 17

The stronger the acid, the weaker its conjugate base.

Front 18

Why does a stronger acid have a weaker conjugate base?

Back 18

The stronger acid wats to give of its H, so it does not want to take the H back when it has become a conjugate base.

Front 19

Why does a weaker acid have a stronger conjugate base?

Back 19

A weak acid does not want to give off its H as readily, so it wants to take the H back when it has become a conjugate base.

Front 20

What does the ratio of pKa values tell us?

Back 20

Give an indication of the equilibirium constant for the reaction bewteen a base and an acid.

Front 21

What does the difference in pKas tell us?

Back 21

Give the log of the equilibirum constant.

Front 22

What is the strongest base in aqueous solution?

Back 22

OH-

Front 23

What is the strongest acid in aqueous solution?

Back 23

H3O+

Front 24

What happens to the concentration of OH- in an aqueous solution when a stronger base is added?

Back 24

Concentratin of OH- increases, because more water molecules are deprotonated.

Front 25

What happens to the concentration of H3O+ in an aqueous solution when a stronger acid is added?

Back 25

Concentratin of H3O+ increases, because more water molecules are protonated.

Front 26

As conjugate bases become more stable, do they become more or less basic?

Back 26

Less basic

(The more stable the conjugate ~ the less basic it is ~ the stronger the acid that yields it)

Front 27

As elements become more electronegative, do they tend to have more or less stable conjugate bases?

Back 27

The more electrognegative the element, the more stable the conjugate base.

Front 28

Are electrons in an sp-orbital higher or lower in energy than those in an sp^2 orbital

Back 28

sp is lower than sp^2, (which is lower than sp^3)B

Front 29

What is the order of stability of anions derived from alkanes, alkenes, and alkynes.

Back 29

Anions from alkynes are more stable than those from alkenes, which are more stable than those from alkanes

Front 30

If pKa is higher, is it more or less stable?

Back 30

More stable ~higher pKa

Front 31

What are 5 ways to stabilize the conjugate base, (A-)?

Back 31

1. Have the charge on an electronegative element
2. Deloclalizing the negative charge over other carbon atoms, or even better, over more electronegative atoms
3. Spreading out the charge over electron-withdrawing groups by teh poliarization of sigma bonds, (inductive)
4. Having the negative charge in an orbital with more s character
5. Becoming aromatic

Front 32

Give an equatoin relating pKa, pKb, and pKw.

Back 32

pKa + pKB = pKw = 14

Front 33

What are the two main factors that determine thestrength of a neutral base?

Back 33

1. HOw accessible the lone pair is
- The higher the energy of the HOMO of the molecule, the more reactive it is, so the stronger of a base.
2. To what extent the resultant positive charged form can be stabilized either by delocalization or by the solvent.
- The lone pair is lowered in energy if it is ion a very electronegative element.

Front 34

As the number of R groups increases, doe shte pKaHs become lower or higher?

Back 34

Lower

Front 35

What 2 factors does basicity result from?

Back 35

1. The increased availability of the lone pair and the stabilization of the resultant positive charge, which increases with successive replacement of hydrogen atoms by alkyl groups
2. The stabilization due to solvation, an important part of which is due to hydrogen bonding; this effect decreases with increasing numbers of alkyl groups.

Front 36

If the lone pair on nitrogen is less available for portonation, is the amine more or less basic?

Back 36

Less basic

Front 37

If the electron density on nitrogen decreases, with the amine be more or less basic?

Back 37

Less basic, because the lone pair is less available for protonation.

Front 38

What are 4 ways to decrease the electron density on a nitrogen, (thereby making it less basic)?

Back 38

1. Nitrogen atom is attached to an electron-withdrawing group
2. Long pair is in an sp or sp^2 hybridized orbital
3. Lone pair is conjugated with an electron-withdrawing group
4. Lone pair is involved in maintaining hte aromaticity of the molecule

Front 39

What is an amidine?

Back 39

The nitrogen equivalent of an amide, (a C-NH gropu replaces the carbonyl)

Front 40

What type of bases are amidines?

Back 40

Among the strongest neutral bases.

Front 41

The numver of electronegative atoms on which to stabilize positive charge corrleates with what characteristic?

Back 41

As the # of electronegative atoms on which to stabilize positive charge increases, so does the stability of basicity

Front 42

What are tautomers?

Back 42

Isomers differing only in the positions of hydrogen atoms and electrons.