Physical properties, analytical chemistry

Question 1

What is the definition of a physical property?

Answer 1

characteristic of matter that can be measured or observed without a change in its chemical composition

Question 2

What is an intensive property?

Answer 2

not depend on the amount of substance (i.e. temperature)

Question 3

What is an extensive property?

Answer 3

depend on the amount of substance (i.e. mass, volume)

Question 4

What is a chemical property?

Answer 4

can be measured by changing the chemical composition of a substance

Question 5

What makes up the physical properties of a drug molecule?

Answer 5

*melting point
*packing (lattice structure destroyed by impurities)
*melting point of water (ice point)
*boiling point
*hydrogen bonding
*carboxylic high bp
*Hydrophilicity or lipophobicity
*Lipophilicity or hydrophobicity

Question 6

What is the bond polarity and bond angle dipole moments equation?

Answer 6

µ = 𝞭 x d (amount of charge x distance between charges)

Question 7

What is the polarity of a molecule?

Answer 7

indicated by the molecular dipole moment
of the entire molecule

Question 8

What are the types of solutes in solvents solubility?

Answer 8

polar solute in polar solvent = dissolves
polar solute in non polar solvent = does not dissolve
non polar solute in non polar solvent = dissolves
non polar solute in polar solvent = does not dissolve

Question 9

What is the partition law?

Answer 9

‘a given substance, at a given temperature, will partition itself between two immiscible solvents in a constant ratio of concentrations’

Question 10

Weak base/ weak acid and partition coefficient

Answer 10

Fully ionised molecule (charged): fully soluble in water
Non-ionised molecule: fully soluble in organic solvent
Partition coefficient: depending on the pH at which the measurement is done
P value for acids: measured at low pH when the acid is unionised
P value for bases: measured at high pH to prevent ionisation

Question 11

What is the shake flask method?

Answer 11

1) The two phases are mixed
2) Two phases separate→ the drug is added (flask shaken)
3) Two phases allowed to separate → concentration of drug in the aqueous
phase is then determined (titration, spectrometry).
4) Concentration in the octanol phase: found by subtraction and the value of
P is calculated.

Question 12

Acids + solubility

Answer 12

Acidic molecules: soluble in organic solvents at low pH (unionised, no charge)
soluble in polar solvents at high pH (ionised, charged)

Question 13

Bases + solubility

Answer 13

Basic molecules: soluble in organic solvents at high pH (unionised, no charge)
soluble in water at low values of pH (ionised, charged)

Question 14

What is recrystallisation?

Answer 14

procedure for purifying an impure compound in a solvent (solids only).
Based on the principle that the solubility of most solids increases with increased
temperature

Question 15

What is distillation?

Answer 15

A process where liquids are converted into vapours by heating and followed by
condensation of vapours through cooling

Non-volatile impurities from volatile liquid
Mixtures with liquids having a difference in boiling point

Question 16

What is chromatography?

Answer 16

“Methods for separating a mixture into its components, which may also involve
identify the components and measuring their concentration”
Involves separation of two or more components by distributing between two phases

Question 17

What is the equation used for chromatography?

Answer 17

Partition coefficient P (K)=[solute phase 1]/[solute phase 2]

Question 18

What are the different phases in chromatography + what they represent

Answer 18

Mobile Phase flows through or over the stationary phase
Mobile Phase: gas or liquid
Stationary Phase: solid or liquid supported on a solid

Question 19

Stationary phase: chromatography, what happens?

Answer 19

More polar compounds: form H-bonds with silica → stick to the silica gel more
firmly than the others. Adsorbed more strongly will run less
Less polar compounds: form only weak van der Waals interactions → stick less
to the silica gel → more carried by the mobile phase, will run more
More strongly a compound is adsorbed (more polar is) → less distance
travelled up the plate. Low polarity compounds have higher Rf values (run more)
than higher polarity compounds

Question 20

Chromatography: mobile phase, TLC plate, what happens?

Answer 20

• Ability to dissolve: solubility of compounds (Like dissolves like) in mobile phase
  influence how fast they move up the TLC plate.
  The more soluble they are, the faster they move.
  Polar compounds: run faster in polar solvent
  Non-polar compounds: run faster in non-polar solvents

Question 21

qualitative chromatography, what are some properties of the TLC?

Answer 21

Same principles of TLC:
Non-polar compounds: move down rapidly: will
come out first from column
Polar compounds: travel down slowly or not at all:
will come out very late or will stay in the
column