CGIER 34 - Solubility Equilibria

Question 1

describe chemical equilibrium

Answer 1

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

Question 2

equilibrium constant

Answer 2

K equals concentration of products over concentrations of reactants to the power of their stoichiometric coefficient
K is not assigned to a unit

Question 3

what is the rule involved equilibrium constant expression

Answer 3

you DO NOT include pure solids or pure liquids

Question 4

how does one determine the equilibrium constant of the forward reaction when we know the equilibrium constant of the reverse reaction

Answer 4

Kf = 1/Krev

Question 5

if the K value is greater than 1 it means that the reaction

Answer 5

is product favoured - makes more products than reactants

Question 6

if K value is less than 1 it means that the reaction ..

Answer 6

is reactant favoured - makes more reactants

Question 7

why is solubility phenomena important in physiology

Answer 7

Important for absorption of nutrients
Important for mineralisation processes in biological systems
Applications in drug delivery and diagnostic processes

Question 8

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.___

Answer 8

1. dynamic equilibrium
2. solids
3. ions
4. dissolution (dissolving)
5. precipitation
6. ions
7. constant

Question 9

explain how the rate of dissolution and the rate precipitation is equal in solubility equilibria

Answer 9

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

Question 10

how would one calculate the equilibrium constant of solubility product or Ksp

Answer 10

find concentration of dissolved to the power of their stoichiometric coefficient ONLY because we don’t include pure solids in our equation

Question 11

solubility product constant Ksp

Answer 11

the constant for the equilibrium established between a solid solute and its ions in a saturated solution

Question 12

why do we not include solid in solubility product constant Ksp

Answer 12

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

Question 13

under what conditions can solubility product values change

Answer 13

can have infinite number of values depending on temperature, pH or common ion

Question 14

molar solubility

Answer 14

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)

Question 15

how is molar solubility calculated?

Answer 15

using substances solubility product constant and stoichiometric coefficients of substance components
using units mol/L

Question 16

when is solubility product constant Ksp reliable

Answer 16

only if the solid has the same ratio of cations to anions

Question 17

how does common ions influence solubility

Answer 17

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

Question 18

how does pH influence solubility of solids e.g. decreasing the pH in which the product is basic

Answer 18

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

Question 19

applications of solubility in healthcare

Answer 19

modify substances to favour solubility characteristics for drug development and dental health

Question 20

how can substances with low molar solubility be useful in medicine

Answer 20

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

Question 21

how does solubility affect oral hygiene

Answer 21

bacteria in teeth decrease pH and make the main component of teeth hydroxyapatite more soluble
rate of dissolution is greater than rate of precipitation

Question 22

how does the involvement of molar solubility prove that fluoridation is somewhat beneficial in water treatment

Answer 22

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

Question 23

solubility

Answer 23

how quickly ionic compounds dissociate into their constituent ions

Question 24

how can we modify drug solubility

Answer 24

form it into a salt

Question 25

what are the exceptions to converting drugs into salts to increase solubility

Answer 25

certain counter ions and if the solution contains a common ion

Question 26

solubility of drugs in aqueous media can be very dependent on ___ this can impact ___

Answer 26

salt form ie. type of counter ions

salt of a drug for use in formulations

Question 27

what must be taken into consideration when developing drugs for oral administration?

Answer 27

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