Solutions Flashcards
What are the 3 steps of dissolution?
1) Solid molecule leaves particle
2) Creation of a cavity in the solvent
3) Solute molecule enters the cavity
What is a boundary layer?
-Outside layer of solution where it meets the solid
What is mass transfer?
-The diffusion of dissolved molecule from the boundary layer into the bulk solvent
What determines the dissolution rate?
-Mass transfer with time ?
What does K1 stand for in noyes-whitney equation?
-Dissolution rate constant
What does A stand for in noyes-whitney equation?
-Surface area of undissolved solid drug
What does Cs stand for in noyes-whitney equation?
-Saturated solubility of drug in solvent
What does C stand for in noyes-whitney equation?
-Concentration of drug in solution
What does h stand for in noyes-whitney equation?
-Thickness of boundary layer
How does increasing surface area speed up dissolution?
-More particles are facing the boundary layer so can diffuse to bulk solvent sooner
How can the saturated solubility of drug in solution speed up dissolution?
-As long as the dissolution is endothermic, increasing temperature
-Changing solvent or adding co-solvent
How can the concentration of drug in solution speed up dissolution?
-Increases the volume of solvent or remove dissolved drug from solution
Define solution?
-Mixture of two or more components that form a single phase that is homogeneous on a molecular level
Define solvent ?
-The component that determines the phase
Define solute ?
-The other components that are dispersed as molecules or ions throughout the solvent
Define dissolution?
-The process whereby molecules or ions from the solid phase move into solution
What is a solution?
-A mixture of two or more components that form a single phase that is homogenous to the molecular level
What are two types of pharmaceutical solids?
-Crystalline and amorphous
What is an amorphous solid?
-A solid that lacks an ordered internal structure
What is a solvent?
-The component which determines the phase
What is a solute?
-The other components (S) which are dispersed as molecules or ions throughout the solvent
What is a dissolution?
-The process whereby molecules or ions from the solid phase move into solution
How many phases does a suspension or emulsion have?
-2
What is solid in liquid solution?
-A solution of non-electrolytes (sucrose) or electrolytes that form ions in solution
What is miscibility?
-Mutual solubility of components in liquid/ liquid systems
What is a gas in liquid solution?
-Gas dissolved in liquid
What can gas/liquid solutions be determined by?
-Temperature and pressure
When will dissolution occur?
-When the attractive force between drug molecules and solvent is greater than between drug molecules
What can effect solubility?
-Molecular structure
-Substituent position of functional group on ring
How do polar solvents cause high relative permittivity?
-They dissolve ionic solutes by reducing the force of attraction between oppositely charged ion in crystalline solids
What is the units for relative permittivity ?
-Er
How do semi-polar solvents induce permittivity?
-They can induce a degree of polarity in non-polar solvent molecules which enables polar solutes to be dissolved
Why can’t non-polar solvents dissolve polar solutes?
-Low relative permittivity and lack of h-bonding groups so unable to break covalent bonds
What factors affect solubility?
-Temperature, polymorphism, particle size, pH
How does polymorphism affect solubility?
-Crystalline solids can exist as different polymorphs depending on how the molecules are arranged
-Less stable polymorphs will be more soluble
How does pH affect solubility?
-The more ionised a species, the more soluble it will be
When does dissolution occur?
-When the attractive force between crystal and solvent is greater than between crystal molecules
What letter represents the boundary layer?
-h
How can the speed of mass transfer be increased?
-Increases surface area
-Saturated solubility of drug in solution
-Concentration of drug in solution
-Thickness of boundary layer-agitation
