Chemical Analysis: Paper Chromatography

Question 1

What is the mobile phase?

Answer 1

where the molecules can move, this is always a liquid or a gas

Question 2

What is the stationary phase?

Answer 2

where the molecules can’t move, this can be solid or a thick liquid

Question 3

Why should the base line be drawn in pencil and not ink?

Answer 3

The ink would run on the paper

Question 4

Why should the water level be below the base line?

Answer 4

To prevent the samples dissolving into the water

Question 5

What is the formula to calculate an Rf value?

Answer 5

distance travelled by substance
Rf = ——————————————
distance travelled by solvent

Question 6

What are the stationary and mobile phases in chromatography?

Answer 6

stationary - paper
mobile - solvent (eg. ethanol or water)

Question 7

What effects the amount of time the molecules spend in each phase?

Answer 7

• how soluble they are in the solvent
• how attracted they are to the paper

Question 8

What particles carried further up the paper?

Answer 8

• molecules with a higher solubility in the solvent
• and which are less attracted to the paper
• will spend more time in the mobile phase and they’ll be carried further up the paper

Question 9

What does it mean if a spot is left sitting on the baseline?

Answer 9

• substance is insoluble in that solvent
• could try identifying it using a different solvent

Question 10

Explain how different dyes in a sample are separated by paper chromatography. (4 marks)

Answer 10

1) Solvent moves through paper. (1)
2) Due to different dyes having different solubilities in solvent and different attractions for the paper, they are carried different distances.

Question 11

Explain how different dyes in a sample are separated by paper chromatography. (4 marks)

Answer 11

1) Solvent moves through paper. (1)
2) Due to different dyes having different solubilities in solvent and different attractions for the paper, they are carried different distances.