Physical Chemistry (w8)

Question 1

Define the term physical property …

Answer 1

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

Question 2

Gives some examples of physical properties of a drug molecule …

Answer 2

• colour
• hardness
• mass
• volume
• malleability
• solubility
• density
• melting point/ boiling point
• lipophilicity

Question 3

What do extensive properties depend on ?

Answer 3

They depend on the amount of a substance (mass or volume)

Question 4

What do intensive properties depend on ?

Answer 4

They do not depend on the amount of substance yet are dependant on temperature.

Question 5

List some examples of physical states …

Answer 5

• amorphous solid
• crystalline solid
• hygroscopic solid
• liquid or gas

Question 6

What are dipole- dipole interactions ?

Answer 6

1) Dipole-dipole interactions: interactions between the positive end of one dipole and the negative end of another dipole

Question 7

What are Van der waals forces ?

Answer 7

2) van der Waals Forces: relatively weak forces of attraction that exist between nonpolar molecules. Distance-dependent interactions. Called induced dipole–induced dipole interactions.

Question 8

What is hydrogen bonding ?

Answer 8

3) Hydrogen bonding: attractive force between the H attached to an electronegative atom of one molecule and an electronegative atom of the same (intramolecular) or a different molecule (intermolecular). i.e. H2O

Question 9

What’s the difference in mp between pure and impure compounds ?

Answer 9

The melting point of a pure compound is always higher than the mp of an impure compound

Question 10

What is packing on terms of structure ?

Answer 10

• Packing: how well the individual molecules in a solid fit together in a crystal lattice (symmetrical three-dimensional arrangement of atoms inside a crystal).
• The tighter the crystal lattice, the more energy is required to break it and eventually melt the compound

Question 11

What is boiling point ?

Answer 11

The temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure. Temperature at which a substance can change its state from a liquid to a gas at a given pressure

Question 12

Why do branched alkanes boil at a lower temperature?

Answer 12

They are more compact so have less surface area for force interactions. This means they boil at a lower temperature.

Question 13

What is hyrdophilicity or lipophobicity ?

Answer 13

-The ability of a chemical compound or drug to go into solution in H2O and polar solvents (e.g. MeOH) and have “fear of the fat “.

-Hydrophilic or lipophobic molecule are polar or ionic, forms H-bonds and dipole-dipole with solvent, fat insoluble, cannot cross cell membrane,

-they bind to receptor molecules on the outer surface of target cells

Question 14

What is the polarity of a molecule ?

Answer 14

Is indicated by the molecular dipole moment of the entire molecule

Question 15

What is solubility ?

Answer 15

The amount of a solute that can be dissolved in a specific solvent under given conditions.

Question 16

What do polar substances dissolve in ?

Answer 16

Polar solvents

Question 17

What do non polar substances dissolve in ?

Answer 17

Non polar solvents

Question 18

What is solvation ?

Answer 18

The process of dissolving a solute in a solvent.
(Hydration when solvent is H2O)

Question 19

Why do non polar molecules (no partial charges) not solvate ions very strongly ?

Answer 19

Due to the attractions of the ions in the solid for each other are much greater than their attractions for the solvent

Question 20

What is the partition law ?

Answer 20

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

Question 21

How do you calculate the % of drug extracted ?

Answer 21

Simply the mass of drug in organic phase divided by the total mass of drug

Question 22

What does partition coefficient depend on ?

Answer 22

Vary depending on pH at which the measurement is Carried out

Question 23

What is recrystallisation ?

Answer 23

Procedure for purifying an impure compound in a solvent (solids only.

Question 24

What is distillation ?

Answer 24

A process where liquids are converted into vapors by heating and followed by condensation of vapours though cooling.

Question 25

What is chromatography ?

Answer 25

A method for separating a mixture into its components, which may also involve identifying the components and measuring their concentrations.