Organic - Chromatography

Question 1

What is the mobile phase?

Answer 1

Where the molecules can move. This is always a liquid or gas

Question 2

What is the stationary phase?

Answer 2

Where the molecules can’t move. This must be a solid, or a liquid on a solid support

Question 3

What is the basic principle of chromatography?

Answer 3

1) The mobile phase moves through or over the stationary phase.

2) The distance each substance moves up the plate depends on its solubility in the mobile phase and its retention by the stationary phase.

3) Components that are more soluble in the mobile phase will travel further up the plate

4) Its these differences insolubility and retention by the stationary phase that separate out different substances.

Question 4

What are the 3 types of chromatography?

Answer 4

1) Thin-layer chromatography (TLC)
2) Column chromatography (CC)
3) Gas chromatography (GC)

Question 5

Thin-layer chromatography

Answer 5

• A plate is coated with a solid and a solvent moves up the plate
• The stationary phase is a thin layer of silica or alumina fixed to a glass or metal plate

Question 6

Column chromatography

Answer 6

• A column is packed with a solid and a solvent moves down the column
• Column chromatography is mostly used for purifying an organic product
• as the mixture is washed through the column, its components separate out according to how soluble they are in the mobile phase and how strongly they are adsorbed onto the stationary phase.

Question 7

Gas chromatography

Answer 7

• A column is packed with a solid or with a solid coated by a liquid, and a gas is passed through the column under pressure at high temperatures.
• Used to separate mixtures of volatile solvents
• Can be used to find alcohol levels in blood or urine as well as the proportions of various esters in oils and paints

Question 8

How are colourless chemicals seen on a chromatogram?

Answer 8

1) You can put the plate under a UV lamp and draw around the dark patches to show where the spots are. Many TLC plates have a special fluorescent dye added to the silica or alumina layer that glows when the UV light shines on it.

2) Expose the chromatogram to iodine vapour. Iodine is a locating agent - it sticks to the chemicals on the plate and they’ll show up as brown/purple spots

Question 9

What is the formula for Rf value?

Answer 9

distance travelled by spot / distance travelled by solvent

Question 10

What is gas chromatography-mass spectrometry?

Answer 10

• Combines the benefits of gas chromatography and mass spectrometry to make an analysis tool.
• The sample is separated using gas chromatography, but instead of going to a detector, the separated components are fed into a mass spectrometer.
• The spectrometer produces a mass spectrum for each component, which can be used to identify each one and show what the original sample consisted of.