Flashcards in D2 Medicines: physiochemical properties 2 Deck (18)
Which law deals with vapour partial pressures of solutions introducing real and ideal solutions?
What is an ideal solution?
There are no interactions between dissolved solutes and obey Raoult's Law
What is a real solution?
Interations occur between dissolved solutes which reduce the effective concentration.
What does "activity" describe?
Describes the reduction in effective concentration in real solutions, caused by interactions between solutes.
Activity coefficient equals the activity divided by concentration.
How can we describe solvent-solute interations?
"Like dissolves like" - Water (polar solvent dissolves polar solutes such as sugar and electrolytes).
How do polar solvents dissolve ionic solutes?
Reduce the force of attraction between oppositely charged ions in crystalline solids e.g. sodium bicarbonate
What is relative permittivity?
Indicated how easily a material can become polarised - polar solvents have a high relative permittivity value.
What kind of solvent is able to solvate molecules and ions using dipole-dipole interactions?
Why is Ranitidine HCl better than normal Ranitidine?
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
What kind of solvent can dissolve some polar and some non-polar solutes?
Semi-polar solvents (can induce a degree of polarity in non polar solvent molecules and solvent molecules.
How do non-polar solvents behave?
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
What could be the result of a change in pH?
Solubility of the drug may alter - could improve solubility or could form a precipitate.
How can we determine the solubility of a weak acid at a given pH?
The Henderson Hasselbach equation
What are the consequences of ionising weak acids and bases?
Hydrated and more soluble
What are amphoteric drugs?
Contain both acidic and basic groups. These drug molecules have multiple pKa values --> drug ionised at different pHs
What is the isoelectric point and how is it calculated?
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