L8 - Acid-Base Theory, pH And pKa 1

Question 1

What are drugs either?

Answer 1

• Weak organic acids (e.g. aspirin, ibuprofen)
• Weak organic bases (e.g. morphine, procaine)
• their salts (e.g. ephedrine hydrochloride, sodium ibuprogen)

Question 2

What does the extent of ionisation of a drug have an important effect on?

Answer 2

• absorption
• distribution
• elimination

Question 3

What is a lowry-brønsted acid?

Answer 3

A proton donor

Question 4

What is a lowry-brønsted base?

Answer 4

A proton acceptor

Question 5

What is the dissociation of strong acids/bases like?

Answer 5

Full ionisation / fully ionised

Question 6

What is the dissociation of weak acids/bases like?

Answer 6

Partial ionisation / partially ionised

Question 7

Use CH3COOH as an example of a WA, what are the 2 eqns?

Answer 7

CH3COOH <=> CH3COO- + H+
H2O(base) + H+ <=> H3O+(acid)

H2O can act as either an acid or a base = amphiprotic solvent

Question 8

What is the overall eqn for CH3COOH + H2O?

Answer 8

CH3COOH + H2O <=> CH3COO- + H3O+
Acid1 + base2 <=> base1 + acid2
Conjugate acid-base pairs

Question 9

What is the general eqn for the dissociation of a weak base?

Answer 9

B + H2O <=> BH+ + OH-

B + H3O+ <=> BH+ + H2O

Question 10

What is the dissociation of a WA in aq conditions be represented by?

Answer 10

HA + H2O <=> A- + H3O+

Question 11

What is the Ka for a WA?

Answer 11

Ka = [H3O+][A-]/[HA]

pKa = -logKa

Question 12

What is the acid like when the pKa is lower?

Answer 12

The acid is stronger when the pKa is lower

Question 13

What is the dissociation of a WB in aq conditions be represented as?

Answer 13

B + H2O <=> OH- + BH+

Question 14

What is the Kb for a weak base?

Answer 14

Kb = [OH-][BH+]/[B]

pKb = -logKb

Question 15

What is the base like when the pKb is lower?

Answer 15

The base is stronger when the pKb is lower

Question 16

How are pKa and pKb values of a conjugate acid-base pair linked by?

Answer 16

pKa + pKb = pKw

Question 17

What is the negative log of the dissociation constant (Kw) for water?

Answer 17

At 25C : pKw = 14.00

Question 18

What are amphoteric electrolytes?

Answer 18

Ampholytes
Are electrolytes which can function as either acids or bases (a/a, and proteins)

Question 19

What is a zwitterion?

Answer 19

A structure having both positive and negative charges on the same molecule

Question 20

What are polyprotic drugs?

Answer 20

• acids capable of donating more than one proton
• bases capable of accepting two or more protons

Question 21

How are the stages of dissociation shown for polyprotic drugs?

Answer 21

May be represented by:
- An equilibrium expression
= has a distinct pKa or pKb value

Question 22

What is the general polyprotic acid system like?

Answer 22

HnA + Hn-jA^-j + … + HA^-(n-1) + A^n-

n = # of protons in the parent acid
j = # of protons dissociated from the parent acid