Solubility
No description yet. This curated deck is ready for daily study.
Card preview (24)
Define solubility ?
How much a solute dissolves
Define dissolution ?
How fast the solute goes into the solution
Define saturation point ??
Divides sub saturated,saturated and supersaturated solutions
What does miscibility apply to ?
Both liquids/gases, indicates how well a substance can be mixed
What does saturated mean ?
Maximum dissolved
What does subsaturared mean ?
More can dissolve
What does supersaturated mean ?
More dissolved than normal possible
Are dissolution and solubility always related ?
No as they are different properties
How is solubility and dissolution different in HPMC ?
Hydroxylpropyl methyl cellulose which is used as film coating is highly water soluble but dissolves slowly as it hydrates over hours
What are the 2 stages of dissolution?
Interfacial reaction Diffusion through the boundary layer
What does the rate limiting step mean ?
The slowest step
What is the rate limiting step in the process of dissolution?
Diffusion through the boundary layer
How is a solid drug crystal held together ?
A solid structure crystal is held by cohesive forces which form an orderly arrangement of atoms called a lattice with low entropy and string attraction
What type of cohesive forces hold a solid drug crystal together ?
Ionic bonds for salts Hydrogen bonds Dipole -dipole Induced dipole
What is required for a solid drug crystal to dissolve ?
It requires energy to break from the solid lattice structure which has to be greater than the forces within the lattice
How do solvents contribute dissolution ?
Solvent such as water molecules move around rapidly due to high kinetic energy and collide with the solid surface which has a lattice structure. as the drug molecules leave the solid due to dissolution the gaps are replaced by solvent molecules. For this to occur , the adhesive forces must be greater equal to the cohesive forces in the solid structure This is known as inter facial reaction
How do you solvent molecules move?
They move rapidly due to kinetic energy
What has to happen in order for dissolution to occur ?
The adhesive forces must be greater or equal to the cohesive forces in the solid structure
What if the adhesive forces are lower than the cohesive forces?
Dissolution is difficult, which means you would have a poor soluble drug
What is the liquid phase?
This is when solvent molecules replace the gaps in the solid structure which are left by drug molecules
What is a microscopic void/cavity?
Circle of solvent molecules which require energy to form
What happens before a solute molecule can be fully accommodated within the gaps in liquid phase?
Before a solute molecule can be accommodated, solvent molecules must move apart to form a cavity. Creating this cavity requires energy because solvent–solvent intermolecular forces are disrupted. So basically the solvent molecules also have an interaction which need to be broken in order form a solvent molecule to be in the solution
Why does dissolution require energy?
Increase in temperature increases solvation so makes cavity creation easier
What is a solvation shell?
This is when the solvent creates a circle or surround the solute molecule