Acid-Base and pH III

Question 1

1 acids and bases

Answer 1

two or more acidic or basic functional groups

Question 2

Dibasic acid

Answer 2

2 ionisable groups

Question 3

H2SO4 strongest acid:

Answer 3

two S=O

Question 4

Tribasic acid

Answer 4

3 ionisable groups

Question 5

Loss of a further H+ from an ion is ____ ____ __________than loss of the first H+ from the non-ionised acid (stating acid)

Answer 5

much less favourable

Question 6

It is more _______ to lose a H+ from an anion than from an uncharged molecule

Answer 6

difficult

Question 7

Charge density;

Answer 7

Extra COOH: electron-withdrawing stabilises conjugate base

Question 8

Difference between pKa1 and pKa2 diminishes as -CH2- separating COOH _______

Answer 8

increases

Question 9

After removing the first H from ne COOH: pKa2 < pKa1 COO- electron-donating _______ the dianion

Answer 9

destabilise

Question 10

what is an organic molecule?

Answer 10

When it includes C and H

Question 11

Extra COOH: increases _____

Answer 11

acidity

Question 12

What causes weakness second ionisation

Answer 12

COO-

Question 13

electron withdrawing:

Answer 13

-NH2 and -NH3+

Question 14

Extra -NH2

Answer 14

not very marked effect in pka1 reduction

Question 15

-NH3+

Answer 15

reducing a lot the pka2

Question 16

Oxoacids (HmXOn)
Examples?

Answer 16

HNO3, H2SO4, H3PO4

Question 17

a) HNO3
b) H2SO4
c) H3PO4

Answer 17

a) monobasic
b) dibasic
c) tribasic

Question 18

↑doubly bonded O

Answer 18

drawing electrons from O-H, H easily removed, more acidic

Question 19

↑doubly bonded O

Answer 19

more resonance forms, greater e- delocalisation, more stable conjugate base

Question 20

Acidic and basic oxides: not obvious H+ _____ or _____

Answer 20

donors or acceptors

Question 21

Example of Basic oxide:

Answer 21

NaOH

Question 22

Example of Acidic oxide:

Answer 22

H2SO3

Question 23

What does oxides react with?

Answer 23

Basic oxides react with acids
Acid oxides react with bases

Question 24

Amphoteric:

Answer 24

• react with acids and bases
• have properties of acid and bases

Question 25

What is a Equivalence point?

Answer 25

acid-base → equal stoichiometric amounts

(reaction completed: all acid has been converted to its conjugated base)

Question 26

Titration curve dibasic acid-strong base

Answer 26

2 moles base and 1 mol acid

Question 27

How to know what is the best range for an indicator?

Answer 27

At equivalence point = where the curve is vertical

Question 28

Acid–base interactions:

Answer 28

formation of the weaker acid and the weaker base (most stable species being favoured at equilibrium)

Question 29

Large pKa difference means…

Answer 29

reaction irreversible

Question 30

In aqueous solution = H2O ______ H+ to any base ______ than OH-

Answer 30

donate
stronger

Question 31

To use bases that are stronger than OH-

Answer 31

solvent weaker acid than H2O

Question 32

Hydrocarbons or ethers (pKa 50), ammonia (pKa 38): Strong or weak acid?

Answer 32

Very weak acid

Question 33

Amphoteric compounds

Answer 33

amino acids = can react with acid and bases (depending on conditions)

Question 34

Amphiprotic compounds

Answer 34

can act as a proton donor and as a proton acceptor

Question 35

What do Amino acids contain?

Answer 35

amphoteric compounds contain separate acidic and basic groups

Question 36

What is a Zwitterion?

Answer 36

doubly charged form

Question 37

Are amino acids ionic compounds?

Answer 37

Yes

Question 38

ammonium cation
pH high or low?

Answer 38

ACIDIC - low

Question 39

aminocarboxylate anion
pH high or low?

Answer 39

BASIC - high

Question 40

pI=pH = pka1 + pka2 / 2

Answer 40

Ka1 = [H+] [zwitterion] / [cation]

Ka2 = [H+] [anion] / [zwitterion]

Question 41

Amino acids: positively charged at low (acidic) pH, negatively charged at high (basic) pH and zwitterionic at neutral pH

Answer 41

Implications for the oral absorption and bioavailability of amino acids from the diet

Question 42

Proteins:

Answer 42

polyelectrolyte whose properties depend on the balance of acidic and basic groups on the side-chains

Question 43

1) Shift in pH by one unit to either side of the pKa must change the ratio
of ionised to non-ionised forms by a factor of 10

Answer 43

pH = pKa +log [ionised]/ [non-ionised]
pH = pKa + 1 [ionised] / [non-ionised] = 10

10/1
[ionised] 10 times

Question 44

2) pH = pKa - 1 [ionised]/ [non-ionised] = 0.1

Answer 44

1/10

Question 45

for a weak base

Answer 45

pH = pKa + log - [B] / [BH+]
pH = pKa + log [base]/[acid]

log [base] [acid] = log [non-ionised-[ionised]

Question 46

For drugs that are weak acids : calculate fraction of the total dose that is ionised for any pH if the pKa is known

Answer 46

Fraction [ionised] = 1 / 1+ antilog (pKa - pH)
% ionised = 100/ 1+ antilog (pka –pH)

Question 47

For drugs that are weak bases: calculate fraction of the total dose that is ionised for any pH if the pKa is known

Answer 47

Fraction [ionised] = 1/ 1 + antilog (pH - pKa)
% ionised = 100/ 1 + antilog (pKa - pH)

Question 48

pH of blood plasma:

Answer 48

7.4
gastric juice is strongly acidic (pH from about 1 to 7), and urine can vary from about 4.8 to 7.5.

Question 49

Very weak acids:

Answer 49

pKa >7.5, non-ionised at pH 1–8, absorption will be largely independent of pH.

Question 50

Acids: 2.5 < pKa >7.5

Answer 50

significant changes in the proportion of non-ionised drug according to the pH. As the pH rises, % of non- ionised drug decreases, and absorption therefore also decreases.

Question 51

Stronger acids: 2.5 <pKa , depend upon pH

Answer 51

fraction non-ionised very low except under the most acidic conditions in the stomach. Absorption is typically low, even under acidic conditions.

Question 52

Basic drugs, absorbed?

Answer 52

not absorbed from the stomach, where the pH is strongly acidic.