dissolution and solubility

Question 1

what is the debit on of dissolution

Answer 1

the process by which a solid substances enter into a solvent to form a solution

Question 2

what is the definition of a solution

Answer 2

this is a homogenous single phas mixture on the molecular level

Question 3

what is the decision of solubility

Answer 3

amount of a substance that passes into solution

Question 4

what is the rate of dissolution

Answer 4

the amount of drug substance that goes in solution per unit time under standardised conditions of liquid/solid interface, temperature and solvent composition

Question 5

what is the dissolution theory - diffusion layer model

Answer 5

1) interfacial stage - this is when the solvent will form a cavity, where a solute molecule in in the centre of it

2) diffusion through the boundary layer - due to this interfacial reaction a boundary/ diffusion layer forms around the solid drug particles

this forms a boundary around the drug, this drug then needs to diffuse from an area of high to low but this layer can make it harder for this to occur

how can you get rid of this - this layer can be disrupted by stirring or peristaltic system will disrupt it

Question 6

what are the energy changes during dissolution

Answer 6

1. the solute requires energy to break one solute molecule- ENDOTHERMIC
2. the solvent then needs to form a cavity and this requires energy - ENDOTHERMIC.
3. it gives or takes energy for the solute molecule to go in the cavity as bonds are made - ENDOTHERMIC/EXOTHERMIC

Question 7

what factors which affect the dissolution rate

Answer 7

1. by increasing the sa the dissolution rate will increase - such as crushing a tablet
2. by increasing the solubility of the solute it will increase the rate of dissolution
3. by decreasing the diffusion pathway it will increase the rate of dissolution

Question 8

what is the notes whitney equation

Answer 8

dm/dt = DA( Cs - C)/h

D - dissolution co efficient
A - surface area
Cs - drug solubility
C - drug concerntration in given time
h - diffusion layer

Question 9

how can you see that something is soluble

Answer 9

• if a solute of 1g is able to be dissolved in less than 1ml of solvent

and if given in a percentage - if the percentage solubility is closer to 100% it is more soluble

Question 10

what are factors which affect solubility

Answer 10

structural features

1) sa
2) melting and boiling point - low melting/boiling point will increase the solubility because they have less strong bonds
3) crystal characteristics polymerism -

external factors

1) an increase in temp increases the solubility only if the process is endothermic. if exothermic the rate will decrease
2) CoSolvent - this is when you mix two solvents together because the solute is more soluble in one of them- for example of the solute is more soluble in ethanol, there would be a higher proportion of ethanol than water
3) pH - this is because most drugs contain ionisable groups