O Chem Purification Techniques

How does distillation work?

Separates liquids based on boiling points and the liquid with the lowest BP is collected first

When do you use simple distillation?

When boiling points are at least 25 C apart, and overall less than 150 C.

How does vacuum distillation affect boiling point?

Decreases boiling point because the pressure increases. Should be used if the BPs are over 150 C.

What distillation technique is best when BPs are less than 25 C apart?

Fractional Distillation

Cation exchange

Uses a negative stationary phase, and negative molecules elute first

Anion exchange

Uses a positive stationary phase, and positive molecules elute first

Thin Layer Chromatography

Silica coated sheet shows polar molecules stick and have lower Rf than nonpolar molecules.

HPLC

uses high pressure to pass solvent phase through finely ground stationary phase.

Gas Chromatography

similar to HPLC, but requires a volatile gas sample. Molecules with higher boiling points have longer retention times.

When separating larger molecules, what type of gel should be used in gel electrophoresis?

agarose gel

When separating smaller molecules, what type of gel should be used in gel electrophoresis?

polyacrylamide gel

List functional groups from highest to lowest boiling points.

amide>carboxylic acid>alcohol>ketone/aldehyde>amine>ester>ether>alkane