D2 Medicines: physiochemical properties 2

Question 1

Which law deals with vapour partial pressures of solutions introducing real and ideal solutions?

Answer 1

Raoult’s Law

Question 2

What is an ideal solution?

Answer 2

There are no interactions between dissolved solutes and obey Raoult’s Law

Question 3

What is a real solution?

Answer 3

Interations occur between dissolved solutes which reduce the effective concentration.

Question 4

What does “activity” describe?

Answer 4

Describes the reduction in effective concentration in real solutions, caused by interactions between solutes.

Question 5

Activity coefficient

Answer 5

Activity coefficient equals the activity divided by concentration.

Question 6

How can we describe solvent-solute interations?

Answer 6

“Like dissolves like” - Water (polar solvent dissolves polar solutes such as sugar and electrolytes).

Question 7

How do polar solvents dissolve ionic solutes?

Answer 7

Reduce the force of attraction between oppositely charged ions in crystalline solids e.g. sodium bicarbonate

Question 8

What is relative permittivity?

Answer 8

Indicated how easily a material can become polarised - polar solvents have a high relative permittivity value.

Question 9

What kind of solvent is able to solvate molecules and ions using dipole-dipole interactions?

Answer 9

Polar solvents

Question 10

Why is Ranitidine HCl better than normal Ranitidine?

Answer 10

As a free base, ranitidine has poor aqueous solubility, but to be absorbed it needs to be in solution.
By reacting ranitidine with strong HCl the salt ranitidine is produced and as an ionised form, is more aqueous soluble

Question 11

What kind of solvent can dissolve some polar and some non-polar solutes?

Answer 11

Semi-polar solvents (can induce a degree of polarity in non polar solvent molecules and solvent molecules.

Question 12

How do non-polar solvents behave?

Answer 12

Non polar solvents can dissolve non-polar solutes however due to a low dielectric point/permittivity, they cannot polarise the solutes or break any covalent bonds.
Held in solution by VDW forces

Question 13

What could be the result of a change in pH?

Answer 13

Solubility of the drug may alter - could improve solubility or could form a precipitate.

Question 14

How can we determine the solubility of a weak acid at a given pH?

Answer 14

The Henderson Hasselbach equation

Question 15

What are the consequences of ionising weak acids and bases?

Answer 15

Hydrated and more soluble

Question 16

What are amphoteric drugs?

Answer 16

Contain both acidic and basic groups. These drug molecules have multiple pKa values –> drug ionised at different pHs

Question 17

What is the isoelectric point and how is it calculated?

Answer 17

The pH at which the molecule has no net charge i.e. equal dissociation of acidic and basic groups.
Calculated by pKa1 + pKa2 divided by 2

Question 18

When are amphoteric drugs least soluble?

Answer 18

At the isoelectric point when their is no net charge