L9 - Acid Base Theory, pH And pKa 2

Question 1

What is the degree to which these drugs are ionised dependent on?

Answer 1

pH
- pH solution
- pH of target organ

Question 2

What important effect does the extent of ionisation have?

Answer 2

• absorption
• distribution
  -elimation

Question 3

How to calculate pH of weak acids? Henderson-hasselbalch eqn

Answer 3

HA + H2O = A- + H3O+

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

Question 4

How to calculate pH for a weak base? Henderson-hasselbalch eqn

Answer 4

B + H2O = OH- + BH-

pH = pKa + log([B]/[BH-])

Question 5

What is the general henserson-hasselbalch eqn?

Answer 5

pH = pKa + log([conj base]/conj acid])

Question 6

What is the henderson-hasselbalch eqn used for?

Answer 6

Allows the ratio of ionised to unionised drug to be calculated at any pH

Question 7

How do you re-arrange the equation to determine the mole ratio of conjugate acid-base species?

Answer 7

([conj base]/[conj acid]) = antilog(pH-pKa)

Question 8

What is used as a conjugate acid if the conc. is not provided?

Answer 8

1

Question 9

How do you calculate fraction of ionised acid (conj base)?

Answer 9

([conj base]/[conj acid] + [conj base])

Question 10

On pH dissociation profiles for weak acids and bases, when does pKa = pH?

Answer 10

At 50% of species being ionised