Chromatography Flashcards
Define chromatography
The separation of two or more compounds or ions caused by their molecular ion interaction with two phases
What two kinds of chromatography did we perform?
Thin layer and column
What are the two phases mentioned in the definition of chromatography?
Mobile and stationary
Describe the mobile phase
This is also called the eluent phase. It is just a solvent.
What makes up the TLC?
A plate (it can be glass, metal, or plastic), ours are plastic; and a thin layer of silica gel coating the plate
Describe the stationary phase.
This is actually doing the separation. The most common are silica gel and alumina.
Which is more polar: silica gel or alumina?
Alumina
What does silica gel look like?
There is a Si atom in the middle with four oxygens. Each of those oxygens is connected to another Si atom.
How do we set up our TLC plates?
Draw a line with a pencil about 1 cm from the bottom, dip a capillary tube into the solution, spot it onto the plate
Why can we not use pen to make the marking on the TLC plate?
The ink from the pen will separate and move up the plate and we don’t want to see the ink.
Why can we not use a mechanical pencil to make the marking on the TLC plate?
The mechanical pencil will scratch the silica gel
What three things are we spotting on the TLC plate?
Mixture, Pure ferrocene, and Pure acetyl ferrocene
What do we do after our TLC plate is set up?
Place the plate into a beaker that has a solvent level below the 1 cm line on the plate, and cover the beaker with foil
What happens if the solvent level is above the 1 cm line on the TLC plate?
The compounds will dissolve off of the plate
What causes the solvent to move up the page?
Capillary action
Which compounds will move faster: polar or nonpolar? Why?
Nonpolar, because the polar compounds will stick very tightly to the stationary phase
How to calculate Rf value?
Rf= (distance spot moves)/(distance the solvent moves)
Why is the choice of solvent important?
If the solvent is too nonpolar, the spot won’t move at all.
If the solvent is too polar, the spot will travel with the solvent front.
What solvent did we use for the thin layer chromatography?
Toulene and ethanol (30:1)
Which solvent did we use for the column chromatography?
Alumina
How do you set up the column chromatography?
Large layer of alumina, mixture, and sand in that order
Why does the column need to be level?
If the bands are not level, the runoff will be contaminated and they will not separate.
Why did we use sand in the column chromatography?
The sand protects the balanced surface of the mixture to allow the compounds to runoff eveny.
What is the order of elution of our list of compounds?
In order for TLC plate and in reverse order for column:
What would happen if a solvent of too high a polarity was used to run a TLC?
What would be the result of not rinsing the tip after eluting the first compound from the
column?
How would having an air bubble in your column affect your separation?
What order of elution (from top to bottom) should be observed for phenol, malonic acid,
benzene, and methyl benzoate if you were separating these compound on a column?
Why is it important that there are no air bubbles in the column?
It slows everything down and makes the path uneven. This can cause the separation to fail and the products will remain impure.
