Introduction of solutions Flashcards
what is a solution ?
a solution is defined as a mixture of two or more components that are formed one phase that is homogenously down to one molecular level
Advantage of solutions
Drug is immediately available for absorption
can be designed for any route of absorption
easy to manufacture
facilitates swallowing in difficult cases
what are the disadvantages of solutions
drug may have low solubility
drug stability can be reduced
unpleasant taste needs to be masked
problems with accuracy when measuring doses
what is solubility ?
the solubility of a solute is its concentration in a saturated solution at a stated temperature
what is a solvent and a solute ?
Solvent - phase in which dispersion occurs
Solute - compound which is dispersed as molecules or ions in the solvent
what is dissolution ?
the process of solid molecules or ions forming a solution is known as dissolution
why are some compounds soluble
drugs will dissolve in water if drug-water interaction is more favourable energetically than average of drug-drug and water-water interactions. This is determined by thermodynamic factors.
will dissolution occur spontaneously
Delta G must be negative in order for the process of dissolution to occur spontaneously at a constant pressure. In most cases delta H is positive, this means for dissolution to occur, the driving force must be an in increase in delta s.
Increasing temp will also tend to promote solution formation.
Generally Delta s will tend to increase as solute molecules become more randomly distributed in solution.
what is the effect of temperature on solubility ?
increasing temp will increase the solubility of a solid of a solid that has a positive heat of solution. Similarly, for an exothermic process, so heat given out, increasing the temp decreases the solubility of a solid.
why should you use heat when making a solution
in order to increase the rate of dissolution
Solubility and dissolution rate
solubility and dissolution rate are not the same. However the high solubility is usually associated with a high dissolution rate.
