W8 Physical properties, analytical chemistry, purity determination and compounds separation Flashcards
What is meant by solubility?
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
What is meant by “Like dissolves like.” (polarity)
Polar substances dissolve in polar solvents, and
nonpolar substances dissolve in nonpolar solvents
Polar Solute in a Polar Solvent
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
What is the Partition coefficient?
What is the Partition law?
P= [organic]/[aqueous]
‘A given substance, at a given temp will partition itself between two immiscible solvents, in a constant ratio of concentrations’
Low pKa means?
Highly acidic
What is meant by physical properties of drugs?
What are some examples of physical properties?
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
What is chromatography?
A method for separating a mixture into components (may also involve identifying compounds and measuring their concentration
What are the names of the mobile and stationary phases on the TLC plate?
Mobile- gas or liquid (silica gel)
Stationary- Solid or liquid supported on a solid (TLC plate)
How do you calculate Rf?
Distance travelled by compound/distance travelled by solvent
(smaller/larger)
What will happen to the melting point if there is an impurity?
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.
What are intensive and extensive properties?
Intensive- Not depending on amount of substance e.g. temperature
Extensive- Depending on the amount of substance e.g. mass or volume
What are some physical states?
amorphous solid, crystalline solid, hygroscopic solid, liquid or gas
What are the 3 types of IMF?
- Dipole-dipole forces
- Van der Waals forces (weak)
- Hydrogen bonding (NOF)
What are dipole-dipole interactions?
Interactions between the positive end of one dipole and the negative end of another dipole
What are van der Waals forces?
Relatively weak forces of attraction that exist between NONPOLAR molecules. Distance-dependent interactions called induced dipole-dipole interactions.
What are Hydrogen bonds?
Attractive forces between H attached to an electronegative atom of one molecule and an electronegative atom of another (or same) molecule i.e. H2O
What is the melting point? How does this relate to pure and impure compounds?
What is packing?
- 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
What is the boiling point?
The temp at which a substance changes state from a liquid to a gas at a given pressure.
For info:
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
What is the effect of Branching?
Decreases the surface area for contact with other molecules, so less IMF are formed, is boiling temperature decreases.
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
B= Recrystallisation
P app
P app is the same of the P tru when the compound is completely non-ionised
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
A= Soluble in organic solvents at a LOW pH and soluble in polar solvents at a high pH.
To see a very polar compound moving up in a TLC plate, you should use…
(like for like)
A polar solvent ABLE to dissolve the compound
Which of the following is a purity determination method
NMR
Recristallisation
TLC
Distillation
mp
TLC
