W8 Physical properties, analytical chemistry, purity determination and compounds separation

Question 1

What is meant by solubility?

Answer 1

Amount of a solute that can be dissolved in a specific solvent under given conditions. Measure of how much of the solute can be dissolved into the
solvent at a specific temperature

Question 2

What is meant by “Like dissolves like.” (polarity)

Answer 2

Polar substances dissolve in polar solvents, and
nonpolar substances dissolve in nonpolar solvents

Question 3

Polar Solute in a Polar Solvent

Answer 3

Dissolves)
The process of dissolving solute in
solvent is called solvation, or
hydration when the solvent is H2O
H2O molecules surround each ion,
with the appropriate end of the
dipole moment next to the ion

Question 4

What is the Partition coefficient?
What is the Partition law?

Answer 4

P= [organic]/[aqueous]
‘A given substance, at a given temp will partition itself between two immiscible solvents, in a constant ratio of concentrations’

Question 5

Low pKa means?

Answer 5

Highly acidic

Question 6

What is meant by physical properties of drugs?
What are some examples of physical properties?

Answer 6

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

colour, hardness, mass, volume, malleability, solubility, electrical conductivity, density, lipophilicity, melting point, boiling point

Question 7

What is chromatography?

Answer 7

A method for separating a mixture into components (may also involve identifying compounds and measuring their concentration

Question 8

What are the names of the mobile and stationary phases on the TLC plate?

Answer 8

Mobile- gas or liquid (silica gel)
Stationary- Solid or liquid supported on a solid (TLC plate)

Question 9

How do you calculate Rf?

Answer 9

Distance travelled by compound/distance travelled by solvent
(smaller/larger)

Question 10

What will happen to the melting point if there is an impurity?

Answer 10

Melting point is lower and also boiling point change.
TLC- if your substance is pure (no impurities present) you should only see ONE spot in your plate after a run.

Question 11

What are intensive and extensive properties?

Answer 11

Intensive- Not depending on amount of substance e.g. temperature

Extensive- Depending on the amount of substance e.g. mass or volume

Question 12

What are some physical states?

Answer 12

amorphous solid, crystalline solid, hygroscopic solid, liquid or gas

Question 13

What are the 3 types of IMF?

Answer 13

1. Dipole-dipole forces
2. Van der Waals forces (weak)
3. Hydrogen bonding (NOF)

Question 14

What are dipole-dipole interactions?

Answer 14

Interactions between the positive end of one dipole and the negative end of another dipole

Question 15

What are van der Waals forces?

Answer 15

Relatively weak forces of attraction that exist between NONPOLAR molecules. Distance-dependent interactions called induced dipole-dipole interactions.

Question 16

What are Hydrogen bonds?

Answer 16

Attractive forces between H attached to an electronegative atom of one molecule and an electronegative atom of another (or same) molecule i.e. H2O

Question 17

What is the melting point? How does this relate to pure and impure compounds?
What is packing?

Answer 17

• The temperature at which a solid becomes a liquid.
• An impure compound always has a lower mp
• Packing= crystal lattice. How well the individual molecules fit together in a 3D arrangement. The tighter the lattice, more energy required to break the IMF and melt it

Question 18

What is the boiling point?

Answer 18

The temp at which a substance changes state from a liquid to a gas at a given pressure.

Question 19

For info:

Answer 19

bp increases as the molecular size
increases:van der Waals forces depends on the area
of contact between the molecules
* the greater the area of contact, the
stronger are the van der Waals forces
* the greater the amount of energy
required to overcome these forces
* branched alkane: are more compact, less
surface area for force interactions. Boils
at a lower temperature

Question 20

What is the effect of Branching?

Answer 20

Decreases the surface area for contact with other molecules, so less IMF are formed, is boiling temperature decreases.

Question 21

A mixture contain two SOLID compounds: A and B. Compound A is soluble only in hot water, while B is soluble in water at any temperature. Which would be the most indicated and fastest purification method?

a. Distillation
b. Recrystallisation
c. Column Chromatography

Answer 21

B= Recrystallisation

Question 22

P app

Answer 22

P app is the same of the P tru when the compound is completely non-ionised

Question 23

An acidic molecule is…?

a. soluble in organic solvents at low pH and soluble in polar solvents at high pH
b. soluble in organic solvents and water at low pH
c. soluble in organic solvents when the pH is high and soluble in water at low values of pH
d. soluble in organic and polar solvents when the pH is high

Answer 23

A= Soluble in organic solvents at a LOW pH and soluble in polar solvents at a high pH.

Question 24

To see a very polar compound moving up in a TLC plate, you should use…
(like for like)

Answer 24

A polar solvent ABLE to dissolve the compound

Question 25

Which of the following is a purity determination method

NMR
Recristallisation
TLC
Distillation
mp

Answer 25

TLC