Define a solution
A solution is a chemically and physically homogenous mixture of two or more components in a single phase system.
What are different types of solutes and their properties?
Non-electrolyte: substances do not ionise in water
Electrolyte: substances do ionise in water.
- strong electrolyte: completely ionises
- weak electrolyte: partially ionises
What are the 3 types of solution? give examples for each.
gas-liquid: carbonated drink
liquid-liquid: alcohol in water
solid liquid: aqueous sodium chloride solution
How are solute types relevant pharmaceutically?
whether a solute is an electrolyte/not will effect its colligative properties, acid/base behavious, bioavailability and others.
What does molality vs molarity represent?
molality, m; is the moles of solute per 1000g of solvent
molarity, M; moles of solute in 1L of solution
What is a ideal solution?
Solution where no properties of components change other than dilution when mixed to form a solution.
What properties will ideal solutions have?
- no heat is absorbed or evolved during mixing
- no expansion or shrinkage occurs
- weight is constitutive of the averages of components.
What does it mean in terms of forces, for a gas or liquid to be in an ideal solution?
Gas: there is an absence of attractive forces
liquid: there is uniformity of attractive forces.
What is a non-ideal solution?
A solution where upon mixing components, there are changes in properties other than dilution
What law applies to ideal solutions, what does this mean?
Raoult’s law; in an ideal solution, the partial vapour pressure of each constituent is equal to the vapour pressre of the pure component multiplied by its mole fraction. This then adds to give the overall vapour pressure of the solution.
How do non-ideal solutions behave?
The more molecules differ structurally, the greater the difference in their interactions.
- does not obey Raoult’s law
Describe a positive deviation from Raoult’s law.
When adhesive forces are weaker than cohesive forces, particles are immiscible and so vapour pressure is greater than expected.
describe a negative deviation from Raoult’s law
Adhesive interactions are stronger than cohesive interactions, so paritcles are miscible and there is a lower vapour pressure than expected.
What are colligative properties?
Properties governed by number rather than nature of constituents.
- lowering of VP
- BP elevation
- freezing point depression
- increasing osmotic pressure
How does a non-volatile component influence vapour pressure in a system?
Partial vapour pressure of each component in a solution is related to its mole fraction in solution. When one component is non volatile, this has no vapour pressure and so the overall VP of the solution is lowered. This extent will be proportional to the relative number of non-volatile molecules.
How does BP change with VP?
A reduction in VP by containing dissolved solute will require a higher temperature to be needed before vapour pressure = atmospheric pressure, and hence higher BP.
How does pH affect drugs?
pH affects the level of dissociation of a drug, depending on if it is an acid or base. Unionised drugs are better able to pass through membranes and be absorbed.
What are advantages of pharmaceutical solutions?
- easy to swallow
- rapid onset of action
- uniform drug distribution
- flexible dosing
- various ROAs possible
What are disadvantages of pharmaceutical solutions?
- bulky and inconvenient to store and transport
- generally reduced shelf-life compared to solid prep
- suitable media for microbial growth
- dosing issues (by patient)
- more pronounced taste compared to solid form
What are advantages and disadvantages of aqueous solutions?
- high physiological compatiblity
- high dielectric constant for dissolution of ionisable drugs
- lack of selectivity during dissolution
- many drugs susceptible to hydrolysis
Why are non-aqueous solutions used?
To overcome solubility and stability issues of aqueous fluids
- various oils and alcohols are used
- can exhibit sustained release properties.
What are different additives in solutions and what are they used for?
- buffers; biocompatibility and stability
- isotonicity modifiers; biocompatibility
- viscosity modifiers; enhances contact and stability
- preservatives; stability
- anti-oxidants; stability
- sweeteners; acceptability
- flavouring and colouring agents; acceptability
