CGIER 34 - Solubility Equilibria Flashcards
describe chemical equilibrium
reactants are continually converted into products and at the same time products are continually converted into reactants
rate of forward reaction is equal to rate of backward reaction
equilibrium constant
K equals concentration of products over concentrations of reactants to the power of their stoichiometric coefficient
K is not assigned to a unit
what is the rule involved equilibrium constant expression
you DO NOT include pure solids or pure liquids
how does one determine the equilibrium constant of the forward reaction when we know the equilibrium constant of the reverse reaction
Kf = 1/Krev
if the K value is greater than 1 it means that the reaction
is product favoured - makes more products than reactants
if K value is less than 1 it means that the reaction ..
is reactant favoured - makes more reactants
why is solubility phenomena important in physiology
Important for absorption of nutrients
Important for mineralisation processes in biological systems
Applications in drug delivery and diagnostic processes
In saturated solutions:
1. ___ ___ exists between 2.__ and 3. __ in solution the rate of 4.___ will equal the rate of 5.___ the concentration of 6. __ in solution will always be 7.___
- dynamic equilibrium
- solids
- ions
- dissolution (dissolving)
- precipitation
- ions
- constant
explain how the rate of dissolution and the rate precipitation is equal in solubility equilibria
When ionic solid dissolves and dissociates into its constituents ions the concentrations of these ions increase.
at the same time as these ions are being spread across the solution it increase chance of this dissociated ions to collide to form a solid again
how would one calculate the equilibrium constant of solubility product or Ksp
find concentration of dissolved to the power of their stoichiometric coefficient ONLY because we don’t include pure solids in our equation
solubility product constant Ksp
the constant for the equilibrium established between a solid solute and its ions in a saturated solution
why do we not include solid in solubility product constant Ksp
more solid
greater surface area
more solid exposed to solution -> greater solubility
as solubility increases so does precipitation
greater surface area for ions to precipitate
increase chance of ions reforming into a solid
under what conditions can solubility product values change
can have infinite number of values depending on temperature, pH or common ion
molar solubility
the no. moles a substance can be dissolved in 1 litre of solution upon reaching saturation (amount of moles dissolved in a litre of a solution)
how is molar solubility calculated?
using substances solubility product constant and stoichiometric coefficients of substance components
using units mol/L
when is solubility product constant Ksp reliable
only if the solid has the same ratio of cations to anions
how does common ions influence solubility
if a solid is dissolved in a solution in which the solution and solid share a common ion according to Le Chatelier’s Principle some of the common ions will add extra product and that extra product will be used to make reactants, shifts more towards the solid - decreases solubility
how does pH influence solubility of solids e.g. decreasing the pH in which the product is basic
pH decreases when the product is basic = removing product as decreasing pH means you are adding H+
system shifts in favour of product sides and increases products thus increasing solubility
applications of solubility in healthcare
modify substances to favour solubility characteristics for drug development and dental health
how can substances with low molar solubility be useful in medicine
barium sulphate is used as a contrasting agent for diagnostics is administered as a suspension (insoluble in all media so must be administered as tablet, capsule or in this case suspension)
barium is toxic - but its low solubility means it is not absorbed by the patient
how does solubility affect oral hygiene
bacteria in teeth decrease pH and make the main component of teeth hydroxyapatite more soluble
rate of dissolution is greater than rate of precipitation
how does the involvement of molar solubility prove that fluoridation is somewhat beneficial in water treatment
fluorapatite dissociates to release F- ions and NOT OH- ions
as the pH decreases fluorapatite is less soluble and reduces probability of developing tooth decay
solubility
how quickly ionic compounds dissociate into their constituent ions
how can we modify drug solubility
form it into a salt
what are the exceptions to converting drugs into salts to increase solubility
certain counter ions and if the solution contains a common ion
solubility of drugs in aqueous media can be very dependent on ___ this can impact ___
salt form ie. type of counter ions
salt of a drug for use in formulations
what must be taken into consideration when developing drugs for oral administration?
must take into account the high concentrations of Cl- ions in the stomach
poorly soluble salts containing a Cl- counter ion may precipitate and therefore become less available for absorption due to common effect
