Chromatography

Question 1

What is the mobile phase?

Answer 1

Carries the soluble components of the mixture

Question 2

What relationship between a sample and the mobile phase makes the sample move faster?

Answer 2

• More soluble components
• More affinity to the mobile phase

Question 3

What does the stationary phase do?

Answer 3

Holds back components of the mixture that are attracted to it

Question 4

What relationship between a sample and the stationary phase that make the sample move slower?

Answer 4

• More affinity for the stationary phase means that a sample move slower, often attracted by hydrogen bonding

Question 5

How are substances separated by chromatography?

Answer 5

• If suitable stationary and mobile phases are chosen, the balance between affinity will be different thus they move at different rates

Question 6

Why will different substances show different Rf values?

Answer 6

They are bonded differently and have different polarities

Question 7

What would happen to the retention time if the polarity of the stationary phase and the compound are similar?

Answer 7

The retention time increases because the compound interacts stronger with the stationary phase - smaller Rf value

Question 8

What is the stationary phase in TLC?

Answer 8

Plastic or glass sheet coated in silica

Question 9

What are the advantages of TLC over paper chromatography?

Answer 9

• Runs faster
• Smaller amounts of a mixture can be separated

Question 10

How can you observe colourless spots?

Answer 10

• Shine UV light on them
• Spray with a developing agent (turns colourless amino acids spots to purple, also requires heat)

Question 11

How do you calculate the Rf value?

Answer 11

Rf = distance moved by spot/distance moved by solvent front

Question 12

What does Rf value stand for?

Answer 12

Retention factor - a measure of the rate of the movement of a component through the chromatography apparatus

Question 13

What is the stationary phase in gas chromatography?

Answer 13

High boiling liquid adsorbed onto an inert solid support

Question 14

What is the mobile phase in gas chromatography?

Answer 14

An inert gas

Question 15

How does gas chromatography work?

Answer 15

1. A small amount of the volatile mixture is injected into the apparatus
2. The mobile carrier gas carries components in the sample through the capillary column which contains the liquid stationary phase
3. The components slow down as the interact with the liquid stationary phase