paper chromatography

Question 1

What is paper chromatography?

Answer 1

A technique used to identify mixtures in solution

Question 2

Why does chromatography work?

Answer 2

Because some compounds in a mixture will dissolve better than others in the solvent chosen

Question 3

How is paper chromatography carried out?

Answer 3

• a capillary tube is used to dab a spot of the solution on a pencil line near the bottom of a sheet of absorbent chromatography paper
• the paper is then placed in a solvent at the bottom of a beaker or tank
• the solvent is allowed to soak up the paper, running past the spot of mixture

Question 4

What determines how far the components in a mixture travel up the paper?

Answer 4

Their relative solubility (the more soluble a substance is in the solvent, the further up the paper it is carried)

Question 5

How can the compounds in a mixture be identified through chromatography?

Answer 5

Their chromatogram can be compared with others obtained from known substances

Question 6

What is needed to compare chromatograms?

Answer 6

The same solvent at the same temperature as used to generate the data held in a database or book of data must have been used

Question 7

How is the data for chromatograms presented?

Answer 7

As an Rf (retention factor) value

Question 8

What is the retention factor (Rf)?

Answer 8

This is a ratio, calculated by dividing the distance a spot travels up the paper by the distance the solvent front travels

Question 9

What are instrumental techniques used for?

Answer 9

Fighting pollution and healthcare

Question 10

What are the benefits of modern instrumental methods over older methods?

Answer 10

• highly accurate and sensitive
• quicker
• enable very small samples to be analyzed

Question 11

What are the detriments of modern instrumental methods over older methods?

Answer 11

• usually very expensive
• takes special training to use
• gives results that can often be interpreted only by comparison with data from known substances