Chromatography

Question 1

Define chromatography

Answer 1

The separation of two or more compounds or ions caused by their molecular ion interaction with two phases

Question 2

What two kinds of chromatography did we perform?

Answer 2

Thin layer and column

Question 3

What are the two phases mentioned in the definition of chromatography?

Answer 3

Mobile and stationary

Question 4

Describe the mobile phase

Answer 4

This is also called the eluent phase. It is just a solvent.

Question 5

What makes up the TLC?

Answer 5

A plate (it can be glass, metal, or plastic), ours are plastic; and a thin layer of silica gel coating the plate

Question 6

Describe the stationary phase.

Answer 6

This is actually doing the separation. The most common are silica gel and alumina.

Question 7

Which is more polar: silica gel or alumina?

Answer 7

Alumina

Question 8

What does silica gel look like?

Answer 8

There is a Si atom in the middle with four oxygens. Each of those oxygens is connected to another Si atom.

Question 9

How do we set up our TLC plates?

Answer 9

Draw a line with a pencil about 1 cm from the bottom, dip a capillary tube into the solution, spot it onto the plate

Question 10

Why can we not use pen to make the marking on the TLC plate?

Answer 10

The ink from the pen will separate and move up the plate and we don’t want to see the ink.

Question 11

Why can we not use a mechanical pencil to make the marking on the TLC plate?

Answer 11

The mechanical pencil will scratch the silica gel

Question 12

What three things are we spotting on the TLC plate?

Answer 12

Mixture, Pure ferrocene, and Pure acetyl ferrocene

Question 13

What do we do after our TLC plate is set up?

Answer 13

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

Question 14

What happens if the solvent level is above the 1 cm line on the TLC plate?

Answer 14

The compounds will dissolve off of the plate

Question 15

What causes the solvent to move up the page?

Answer 15

Capillary action

Question 16

Which compounds will move faster: polar or nonpolar? Why?

Answer 16

Nonpolar, because the polar compounds will stick very tightly to the stationary phase

Question 17

How to calculate Rf value?

Answer 17

Rf= (distance spot moves)/(distance the solvent moves)

Question 18

Why is the choice of solvent important?

Answer 18

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.

Question 19

What solvent did we use for the thin layer chromatography?

Answer 19

Toulene and ethanol (30:1)

Question 20

Which solvent did we use for the column chromatography?

Answer 20

Alumina

Question 21

How do you set up the column chromatography?

Answer 21

Large layer of alumina, mixture, and sand in that order

Question 22

Why does the column need to be level?

Answer 22

If the bands are not level, the runoff will be contaminated and they will not separate.

Question 23

Why did we use sand in the column chromatography?

Answer 23

The sand protects the balanced surface of the mixture to allow the compounds to runoff eveny.

Question 24

What is the order of elution of our list of compounds?

Answer 24

In order for TLC plate and in reverse order for column:

Question 25

What would happen if a solvent of too high a polarity was used to run a TLC?

Question 26

What would be the result of not rinsing the tip after eluting the first compound from the
column?

Question 27

How would having an air bubble in your column affect your separation?

Question 28

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?

Question 29

Why is it important that there are no air bubbles in the column?

Answer 29

It slows everything down and makes the path uneven. This can cause the separation to fail and the products will remain impure.