L8 - Absorbtion 1 - Solubility Flashcards
1
Q
solubility of a substance
A
- the amount that goes into a solution when equilibrium is established between the solute in solution and the excess (undissolved) substance
2
Q
solution process 3 stages
A
- a drug molecule is ‘removed’ from its crystal
- a cavity from the molecule is created in the solvent
- the drug molecules inserts into this cavity
3
Q
saturated solution
A
- when a solution contains a drug at the limit of its solubility at any given temperature and pressure it is described as saturated
- if the solubility limit is exceeded, solid particles of solute may be present
4
Q
factors that affect the solubility of drugs in solution
A
- temperature
- molecular structure of the drug
- its shape and surface area
- its hydrophobicity and degree of ionisation
- and influence of pH
- nature of solvent
- including pH & cosolvents, solubilising agents
- crystal characteristics
5
Q
Use Le Chatelier’s principle to explain why a solubility of a solute may increase with rise in temperature
A
- if the dissolution process is endothermic (ΔH is -=+ve), when temperature rises, solubility increase
6
Q
how does boiling and melting point affect solubility
A
- in general, higher the melting point, stronger the interactions, more energy needed to for dissolution to occur
7
Q
how does surface area of the drug molecule affect solubility
A
- placing the solute molecule in the solvent cavity requires a number of solute-solvent contact
- the larger the surface area of the molecule, the more solute solvent contacts are formed
8
Q
How does the substituents/polarity/structure affect solubility
A
- polar groups capable of hydrogen bonding with water molecules give higher solubility
- non polar group are hydrophobic and impart low solubility
- ionisation increases solubility
9
Q
why does having hydrophillic elements not make a molecule hydrophillic
A
- consider surface area
