Chromatography (Lab 2)

Question 1

What is chromatography?

Answer 1

A technique used to separate/ purify organic compounds within a mixture.

Question 2

What is the principle/underlying method of chromatography?

Answer 2

It is based on differential distribution of compounds between two phases. A mobile phase and a stationary phase.

Question 3

What is the differential distribution ratio? What’s the formula?

Answer 3

Kd = C1/C2

Question 4

What does it mean that chromatography is based on differential distribution of compounds between two phases?

Answer 4

It means that the different compounds in the mixture will distribute through the two phases at different rates depending on their polarities and how these interact with the two phases. As the mobile phase moves through the stationary phase, it carries with it the compounds - carrying the less polar compound faster. The more polar compound moves at a slower rate because it is more attracted to the stationary phase which is always more polar than the mobile phase.

Question 5

What are the two phases of liquid chromatography? What are they made of?

Answer 5

Mobile and stationary phase.

The mobile phase is a liquid organic solvent. This solvent can be of different polarities, but it’s always less polar than the stationary phase.

The solvents more often used are hexanes such as petroleum ether, and also Et2O and CH2Cl2 (in order of polarity).

Benzene and toluene are also used, and they’re more polar than hexanes but less polar than the other two.

If even more polar solvents are needed, the following can be used:
CHCl3< CH3COOH2CH3< acetone (ketone) < EtOH< MeOH< H2O

Remember like dissolves like. Functional groups.

The stationary phase is solid silica or alumina. Silica is used more often because it’s cheaper. But alumina is more polar.

Question 6

How does polarity affect boiling point?

Answer 6

The more polar a molecule is, the higher the boiling point

Question 7

How does size affect bp?

Answer 7

Larger molecules have higher bp

Question 8

What does it mean that polarities are distribution constants?

Answer 8

That more poor compounds are more attracted to the stationary phase and will move slower, affecting their rate of distribution