solutions

Question 1

What is the pharmaceutical relevanc to dissolution?

Answer 1

*absorption
*formulation
*medicine incompatabilities

Question 2

What is meant by absorption?

Answer 2

drugs usually need to be in (aqueous) solution to be absorbed

Question 3

What is the structure of most drugs + how is this relevant to drugs entering solution?

Answer 3

• most drugs are crystalline in structure
  *If such a drug is to enter solution
  then the individual molecules must
  leave the crystalline particles

Question 4

What can cause for dissolution to occur?

Answer 4

*can only occur if the attractive force between the crystals and solvent molecules is greater than between crystal and crystal

Question 5

How are solute-solvent interactions determined?

Answer 5

Attractive forces between solute and solvent are governed
by the molecular structure of the solid and the nature of
the solvent

Question 6

What impacts aqueous solubility?

Answer 6

• salt formation
• changing functional group
• molecular shape
  *substituent position on a ring
  *hydrophic/hydrophilic property of a functional group

Question 7

How do polar solvents affect the solubilty?

Answer 7

• Polar solvents dissolve ionic solutes by reducing the force
  of attraction between oppositely charged ions in crystalline
  solids, e.g. sodium bicarbonate
• Polar solvents can even break covalent bonds, e.g.

Question 8

What property do polar solvents have?

Answer 8

Polar solvents, e.g. water, methanol, acetic acid, have a
high relative permittivity r (formerly known as the
dielectric constant)

Question 9

What are some examples of semi polar solvents?

Answer 9

*acetone
*ethanol
*dimethyl sulfoxide

Question 10

What are the properties of semi polar solvents?

Answer 10

• Can dissolve polar and non-polar substances
• Solvent molecule dipole moment or H-bonding
  groups enable polar solutes to be dissolved
• Semi-polar solvents can induce a degree of polarity in
  nonpolar molecules, e.g. benzene (which is soluble in
  ethanol)

Question 11

What are some examples of non-polar solvents?

Answer 11

• alkanes
• benzene
• oils and fats

Question 12

What are some properties of non-polar solvents?

Answer 12

• Low relative permittivity r dielectric constant and lack of
  H-bonding groups prevent these solvents from dissolving
  ionic or polar solutes
• Unable to break covalent bonds
• Dissolve non-polar compounds only
• Non-polar solutes are held in solution through van der
  Waals interactions with the solvent

Question 13

What are some other factors that determine solubility?

Answer 13

*temperature
*polymorphism/ solvates/hydrates
*particle size
*pH

Question 14

How does temperature affect solubility?

Answer 14

– Dissolution is usually an endothermic process (heat absorbed) so ↑
in temperature leads to ↑ in solubility
– If exothermic then the reverse occurs

Question 15

How does polymorphism affect solubility?

Answer 15

– Crystalline solids can exist as different polymorphs depending on
how the constituent molecules are arranged
– Structure also altered by incorporation of solvent molecules
(solvates & hydrates)
– Less stable polymorphs (metastable)
will be more soluble