chem exam 2 ~ solubility & chromatography

Solubility

Ability of a substance, the solute, to dissolve in a solvent

the better able the solvate can make strong IMF around entire solution, the more soluble it will be

shorter=more soluble

water wants the highest IMF, while hexane wants the lowest IMF

chromatography

separation of molecules based on their interactions with stationary & mobile phase (based on strongest IMF)

Normal Phase Stationary

relatively polar (silica)

Normal Phase Mobile

relatively non-polar (hexane)

Reverse Phase Stationary

relatively non-polar (C-18)

Reverse Stage Mobile

relatively polar (water)

What does Thin Layer Chromatography compare? What does Column Chromatography Compare?

TLC compares Rf values; C.C compares elution order

Thin Layer Chromatography

Stationary Phase: paper or coating on a plate

Mobile Phase: solvent

Run the TLC: solvent is allowed to move up the plate

Rf Value

spot distance/solvent distance

mobility

should never be greater than 1

closer to 1=molecule moved farther

How to find Rf value using TLC

non-polar molecules make stronger IMF w/ mobile phase (move faster)

polar molecules make stronger IMF w/ stationary phase (move slower)

Column Chromatography

stationary phase poured into column

mobile phase poured on top of stationary

separation of molecules based on IMF

Column Chromatography Elution

Reverse Phase:

mobile=polar (elute first)

stationary=non-polar (elute last)

Spectroscopy (column chromatography)

measure absorbance at various wavelengths; will help identify molecular composition of isolated fraction (x-axis=absorbance & y-axis=wavelength)